Porsche 993 - Everything you would want to know about servicing, repairing, upgrading, adding stuff or buying, much of which applies to a 964 as well.

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Porsche 993 Service Repair Manual

Porsche 993: General Information 

D.I.Y.: Repairing a Porsche

993 Service and repair

964 Service and repair

Upgrading 993

Upgrading 964

Upgrading 911

DIY Servicing

Why DIY

993 Repair information

964 Repair information

How to Repair a 993
How to Repair a 964

Fixing a 993

How to fix a 993

Known issues with a 993
DIY Repairing a Porsche

. Body Fluids, Oil Changes Oil Consumption Leaks & other stuff, This is a BIG deal on a 993 & 964 a MUST read!

Disclaimer: The content of this document relates to the Porsche 993 (911 1995 to1998), also some of its content applies to a 964. I am not a professional automotive technician and some of the opinions expressed in this document are just that, opinions, therefore, please feel free to use this document at your own risk. Many times a lot can be learned by simply watching qualified professionals work on your car.

Excessive Oil Consumption or simply a little blue smoke at startup & the Top-End Rebuild - This is a procedure 993/964 owners are asked to consider by enterprising mechanics. It is made under the conclusion that the valve guides are worn to the point that excessive oil is slipping past them and burning. Oil consumption and or blue smoke at startup alone is never an indication of the need for a top-end rebuild. Blue smoke at a startup usually has to do with oil vapor from the oil tank condensing on the inside of the intake manifold and being drawn into the engine at startup and burning, a perfectly normal condition.

A recent posting on Facebook in a Porsche 993 Group:

"I’m getting blue exhaust when I start the car. My mechanic says it’s a $15 k fix."

 

This is an interesting conclusion in that if excess oil was actually slipping past the valve stems it would have to make it past the valve stem seals first, items that can be replaced with the engine in the car and without removing the heads. Some of the lack of discussion of the valve stem seals may have to do with replacing them is a small job versus swapping out the heads in a top-end rebuild incurring significant billable work.

I recently ran across the following comment in a 993 technical forum in reply to an oil consumption concern:

“How full do you keep the oil tank? When I kept mine at the full level [on the dipstick] I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 [of the range on the dip stick] I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full [on the dash gauge].”

The implication here is that a true measure of a full oil tank is somewhat variable and frequent overfilling may be contributing to the perception of excessive oil consumption where none may exist. Could burning the ingested overfill explain blue smoke at startup or over time misfire problems or clogged secondary air injector ports, potentially a self-inflicted service issue caused by simply overfilling the oil? Seems a lot more feasible as the common root cause than leaking valve stems.

Here is a little more information on diagnosing the need for a top-end rebuild.

Here is a primer on how to read and interpret the oil-related dash gauges in a 993.

I change my own oil - Here is the oil fill procedure I use today to

address the whole overfill conundrum, use it at your own risk as I am not a professional automotive technician. If you have any concerns about aspects of the procedure contact a professional for their advice.

1. If your car still has the under-engine cover/tray remove it and store it away as some folks think it just hides oil leaks and causes the engine to retain heat. I feel it serves little purpose beyond making changing the oil more difficult. It has gone missing on most examples of a 993.
2. Park the car on level ground & engage the parking brake 
3. Break free the right rear wheel's nuts and leave them slightly snug this being the passenger side of USA-delivered cars. The right side of the car is on the right-hand side when you are standing behind the car looking forward. If you use LIFTBARS to lift your car it may be necessary to remove the entire rocker panel cover strip before lifting the car so it doesn't interfere with getting to the oil tank.
4. lift the right rear wheel off the ground and put it on a jack stand. To safely lift a 993/964 a DIY procedure can be found at Jacking Up A 993 Safely
5. Remove the right rear wheel and the front half of the wheel well liner and release the back half of the plastic rocker panel cover strip.
6. There is a rearmost special clip that holds the rocker pannel strip in place on a 993. Many times it is broken and can be replaced if needed. On the 993 Carrera, it is a 999.507.373.00 for wide-body 993 cars it is a 999.591.990.00 
7. I drain the oil tank and the engine case into a drain pan of at least 10 to 12 quarts in capacity. Do not attempt to drain the oil using a vacuum oil remover through the oil filler neck, it will not work and can easily damage or bend the oil level float arm in the oil tank or puncture the filler hose to the tank. The engine case drain plug is on the bottom of the engine case and points to the left side of the car.

   

   Flapper Valve Housing

8.  I reach under the car through the right rear wheel well, and I replace both filters. This requires removing  Phillips screws, hex screws, and plastic hex flange nuts holding the back half of the fender liner, and the back half of the plastic rocker panel cover strip.
9. I then detach the forward-facing red rubber duct from the heating system flapper valve housing (diverter), hanging below the engine, and tuck the duct out of the way. 
   
10. I use large Channel-Locks pliers to initially break loose both the small and large filters. Removing the small filter will be messy, cleaning up after installing the new filter is discussed later in the process. When installing the new filters I rub a little old oil on the rubber seals on the filters before threading them in place. I make both replacement filters as tight as I can with my bare hands and then turn the filter a quarter-turn beyond this with the pliers. Although not a factory method I have never encountered a filter backing off or being unable to remove one with this method. 

• The oil filters are:
• 993-107-203-05* for the small filter;
• 993-207-201-03 for the large one.

• 

  Filter's internal
  anti-drain back
  check valve
  
  

  *If you use an aftermarket branded filter such as MAHLE, BOSCH, or others on the Turbo model be sure to use one that incorporates an internal anti-drain back check valve like the OE filter. Generally, the aftermarket small filter part number crosses to a 993-107-203-03 Porsche part number, and then one of the premium series in that brand under that cross includes the internal check valve. In most cases, the check valve can be seen through the small oil passageway holes in the bottom of the filter when it is compared to one without the valve. The valve is thought to minimize smoking at startup.
• Because of ready availability I used Mobil 1-FS 0W-40 when I lived in Virginia and in the warmer climates of Dallas where I live now I use Mobil 1-FS X2 5W-50. 

If you see your oil pressure gauge regularly dip below 2 Bar at idle under normal operation consider switching to the Mobil 1-FS X2 5W-50 grade. Both of these oils have slightly higher zinc levels of 1100 parts per million which is thought to help extend the life of the valve train in our cars' engines. Other brands with similar published specifications will work just as well. Oil recommendations can be a rancorous discourse in our community, my answer to this is to each their own.I do not disconnect the rigid metal oil tube below and slightly to the rear of the smaller filter on the engine case even though it is specified in the factory procedure. My belief is that breaking the seal on the tube presents an unnecessary leak failure mode and the quantity of oil present in the lines is small. Also, others have found removing a tube that is not removed regularly can be problematic resulting in it being damaged and needing to be replaced, a real pain to do.

 11. I do keep two cans of spray electronic parts cleaner on hand to clean off oil spilled on the engine, suspension, and the flapper valve & duct from removing the smaller filter. 

12. When replacing the engine case and oil tank plugs I replace the crush rings and the "O" ring on the tank plug.

Crush Rings

• The part number for the oil tank drain plug crush ring is 900.123.118.30 and seems to have critical dimensions so the dealer part should be used.

• 

  Oil Tank
  Drain Plug
  O-Ringg

   The engine case drain plug for the MY1995 and earlier is 900.123.118.30 and for MY1996 and later cars, it is 900.123.011.30. The part numbers seem to be interchangeable as they are described as the same A-22mm ID x27mm OD size and are made of aluminum.
• The heat-resistant Viton oil tank drain plug part number 999.701.269.40 is sized at 11x2.5.
•  

13.On occasion, I have reused the existing metal crush rings and heat-resistant "O" ring with no leaks. Be sure not to overtighten the tank plug, both the engine case and oil tank drain plugs are to be tightened to 50Nm (+5/-0 tolerance) or 36.9 ft-lb (+3.7/-0) according to the factory. A lifetime supply of the A22x27 aluminum crush rings and the heat-resistant 11x2.5 Viton (Fluorine rubber) green O-Rings, for the tank plug can be had on eBay or Amazon for a few dollars.

14. Button up the plastic parts, and the heating duct, mount the wheel and lightly snug the wheel nuts, then put the car back on the ground.

15. Re-torque the wheel nuts to the recommended dry thread value of 133Nm. or 98 ft./lb. (dry) in a cross-wheel star pattern sequence, then check the torque values by repeating the sequence on the now-tightened wheel nuts.

16. Refill the oil tank very slowly using a long neck funnel so the oil does not back up in the funnel or in the oil filler pipe's neck and spills out over the top and all over the place. 

• Stuff some rags around the filler neck to catch any incidental overflow.
• Running the engine for a few moments once six or seven quarts have been added charging the oil filters seems to reduce the tendency for the oil to back up when filling the oil tank further.
• Spilled oil is hard to clean up completely and many times shows up days if not weeks later under the car where it is misdiagnosed as a leaking lower right valve cover, go figure?

  

  Long Neck 
  Funnel

17. Fill with 8 quarts +/- of oil and run the engine to a fully warmed state. This can take a 20-minute drive to achieve, looking to the temperature and oil pressure gauges to see if they have settled into their normal operating range.

18. Then, with the engine, still running, add additional oil, a few ounces at a time until oil registers on the dip-stick at approximately 1/4 of its scale with the car on level ground.

Dip-stick

 

• The oil fill difference between the top and bottom of both the dipstick and the gauge is rather small so take your time adding oil in small increments while rechecking the dipstick. 
• If you find yourself putting ten or more quarts of oil in, using this procedure, you are most likely overfilling the engine. On a 993/964 this can have serious operating consequences and so an over-fill should be addressed as soon as possible. The easiest way to address an over-fill is to shut off the engine and drain the oil from the engine case as the case retains a smaller volume of oil, most of the oil is retained in the oil tank. Once drained, it can be added back in, if needed, to readjust the level.

If you are having a shop change your oil for you: 

As of late I have heard of incidents where a Porsche specialty service shop has overfilled the oil. This seems to suggest properly adjusting the oil level in a 993/964 is not universally understood even in the professional Porsche servicing community. Knowing this it may be best when having your 993's oil changed to specify that the technician only put 8 quarts in and no more. Then once you have driven your car home personally adjust the final fill level in your driveway.

If you suddenly experience what appears to be an oil leak shortly after an oil change by others here are the probable causes. 

The final steps I have added with each oil change are to;

Fanbelt Switch

• Put a very small dab of white lithium grease on the center of the side (hub) of the wheel of the fanbelt switch roller. Over time this grease will migrate into the bearing greatly extending its life and so the switch's as well.

Also, consider:

• Pull off the ignition distributor caps and rotors and place a drop or two of motor oil on the center of the shafts under each rotor and the mechanism under the doughnut-shaped plastic spark shield over the mechanism below. This will lubricate and help avoid corrosion forming in the distributor mechanism potentially extending its life considerably. Many forgo this procedure for long periods as the service intervals for the distributor caps are quite long on a 993/964. In the old pre-electronic ignition days when ignition points were changed or adjusted every 1500 miles, adding a drop or two of oil was a standard add-on procedure.

Special considerations for the 993 Turbo Variant and smoking at startup:

Although some folks feel a little smoke at startup is a big problem, an occasional plume of smoke at startup especially if the car has been sitting for a while is normal for these cars and should be of no great concern. In any event, if the smoking still bothers you there are options to potentially minimize oil smoking at startup on the Turbo 964/993. 

 

One theory is when at rest some oil may backflow into the turbo lubricating system and can cause a small quantity of oil to leak internally to the turbos. This oil will burn at startup making for a blue plume of smoke.  Some argue that this is not plausible because at startup the turbos are cold and any oil present will not be hot enough to initially burn and cause immediate smoking. Another theory is that oil vent hoses leading from the turbo and or the oil tank to the intake discharge a small amount oil vapor that condenses on the inside of the intake manifold and this oil is immediatly injested and burns at start-up causing the plume. In any event here is what some have done to minimize smoking at startup.

• Switching to a heavier weight (20W-50W Multigrade) oil,
• Verifying the oil filters used have the internal valving to limit the back-flow such as the  Porsche branded Turbo filters and;
• Making sure the oil is not overfilled (lower 1/4 of dipstick). 

• There is an aftermarket oil inlet check valve
  
  that addresses oil migration from the oil tank to the engine. There are also aftermarket check valve kits some add to the oil feed lines of the turbochargers. I hear that some adapt the 996 Turbo Oil Feed Line Check Valve 99610703079 for use on a 993 as well.
  
  
  

I feel the above oil filling method gives an additional margin of safety in avoiding inadvertently overfilling the 993 with oil. If you decide to follow my measurement procedure and as a follow-up check the fill with the dash gauge and your gauge doesn’t read at about 1/4 of its range the float in the oil tank is a bit out of adjustment. Adjusting the float so the gauge approximately matches the dipstick involves draining the oil tank accessing the oil float in the tank and bending its arm a little. I have done this on my 86’ Carrera and have been told it is not too difficult on the 964/993. If you want to make the adjustment it is something to consider at your next oil change when the tank is drained.

A situation I had with my 86” Carrera and now some have reported the same issue with the 993 is where untrained hands mistakenly remove the cover of one of the

Relief valve locations.

 oil pressure relief valves, items "A" & "B" in the illustration to the right, rather than the oil drain plug on the bottom of the engine case when attempting to drain the oil. If the oil pressure valve relief cover is replaced without first reinstalling the spring/components it retains your engine will immediately have serious lubrication issues. If you happen to open the wrong cap and see some small parts under it, just put it back on with the parts in the same way. Then look for the other cap, the correct one, at the bottom edge of the engine case with its hex plug facing the left side, the driver’s side of the car on USA-delivered cars, to drain your oil. If your car comes back from an oil change with the oil pressure warning light illuminated and or the oil pressure near zero stop driving the car immediately and address the missing oil pressure valve parts that most likely fell into the oil drain pan unnoticed.

Internal Engine Repairs:

I’m going out on a limb a bit, But I feel any road-driven normally aspirated 993 (Carrera) that has been used exclusively for street driving and an occasional club auto-cross should not need any internal engine work beyond replacement valve lifter cartridges until well beyond 150,000 miles. At this point and over the last 27 years some owners have managed to run their cars up in excess of  200,000 miles of use without issue. This suggests the need for internal engine work on a street-driven car should always be suspect and the need validated by multiple persons via multiple diagnostic methods.

Oil Leaks. - At some point in your car's life, it will leak oil. The 993/964 engine is oil-cooled and lubricated and the engine itself, unlike other cars is a vast assemblage of heads, cylinders, case haves, valve covers, oil coolers, and the oil tank, and the list goes on. One can spend a lot of time and money chasing minor oil leaks an expense that contributes little to the driving enjoyment of these cars. In my book, the main reason to fix an oil leak is that it is dripping on the floor and that bothers you or it is dripping on the exhaust and smells bad and the issue returns immediately after cleaning the engine's exhaust as described below. Small leaks other than these or oil wetness on the engine case are not material issues and may be best not bothered with.

Oil Smell and or Smoking. If your car has been exhibiting a burnt oil smell or even minor smoking up through the engine hood louvers some assume they need engine resealing.

This is expensive work where one can spend much money chasing a minor oil leak. It is surprising how even a single drop of oil landing on the exhaust can cause a lot of smoke and smell. Before committing to the expense of eliminating leaks one can simply spray Dawn brand Platmum Powerwash pump bottle spray dish degreaser under the car on top of warm heat exchangers and other exhaust components and then hose it off with a garden hose from below the chassis. This will often eliminate the burning oil smells for a very long time. Once the exhaust is hosed down it may trigger a series of individual or general misfire OBDC codes and illuminate the check engine light (CEL). In this case, just run the car to get the engine good and warm. This will dry off the wet ignition wires. Then clear the code with an OBD Code reader and you are good-to-go!

 Keep in mind even a single drop of oil on a hot exhaust system will produce quite a bit of smoke and an attendant smell.

Interestingly, my car had two apparent oil leaks, one at one of the cylinder head oil return tubes. The other appeared to be on the passenger side lower valve cover dripping on the heat exchanger and smelling up the car, which I am told is a very common occurrence. I researched a DIY valve cover gasket replacement and it seemed simple enough. I went ahead and purchased the new gasket. In preparation, I cleaned the oil off the valve cover and the exhaust using a spray electronic cleaner.

Spray Electronic Cleaner

Afterward, the leak seemingly disappeared. Then I recalled that at my last oil change, I spilled a little oil when filling the engine. I wiped up most of it and hosed off the remainder I could see with the electronic parts cleaning spray. Apparently, it took weeks for unseen oil to migrate to the valve cover and ultimately onto the exhaust. 

In retrospect, I wonder how many valve cover gasket or even valve cover replacements have been done on a 993 due to a botched oil change where cleaning was all that was needed. If you are experiencing a leak from what appears to be the lower right-hand valve cover just clean it off with some spray electronic cleaner first and see if it resolves the leak. Also if you are experiencing what appears to be an oil leak after a recent oil change here is a page describing the potential root causes.

 

Valve Covers:

Seeing that these cars are over +26 years old and many have well over 100K miles on them valve cover sealing gaskets seem to be the most common source of an oil leak. If the gasket is replaced properly, the valve covers shouldn't be problematic for a very long time. The gasket is relatively inexpensive to replace. I find it not to be a fun DIY job gaining access to the mounting capscrews to remove and reinstall the covers so I leave it to the professionals to do. There are 4 covers & gaskets and there is no need to replace any gasket other than the one that has proven to be leaking. Replacing all 4 at once is a common stealth up-sell that adds unnecessary expense. 

Quite regularly I hear about the desire to replace the plastic valve covers because they leak or could be warped. Turns out if one looks at the design of the gasket shown below it surrounds each mounting bolt isolating them from the sealing function and is a three-dimensional synthetic rubber material. When used in conjunction with the cover it becomes clear that the sealing process is designed so any aspect of what might be leaking is replaced when the gasket is replaced. As far as warping goes the covers are a lot softer than the head and are held down by quite a few fasteners warping, if even possible, really is not an issue. 

Valve Cover Gasket

For these reasons, the valve covers have turned out to have a very long service life, in most cases beyond the life of the car and so there is really no benefit in replacing them. This is why replacing them with aftermarket metal ones has fallen out of favor in the 993 community.

My experience is that one will end up replacing the valve cover gaskets once or twice in the life of the car usually as part of servicing something under the covers such as the hydraulic lifter adjusting cartridges. I have a theory that in some cases valve cover leaks are the result of removing the valve covers for other reasons or because of an oil change spill that was misdiagnosed as a valve cover leak and subsequently the new gaskets do not get properly installed. This results in a future leaking problem a few thousand miles later. Part of this theory is that I doubt most technicians use a torque wrench to ensure the cover capscrews are tensioned properly simply because there isn't the clearance needed to fit such a wrench without the disassembly of other components.

 A Porsche technician once told me that if properly installed the 993 valve covers rarely leak. He informed me that leaks are usually the result of under-torquing the mounting bolts, the factory spec. is 9.7NM, or tightening them up in the wrong order. My understanding is the correct order is from the center out, alternating between the top and bottom of the cover although I have not been able to get validation in a factory document for this. I suspect the torque value and the tightening sequence are available from Porsche if one was to ask at a dealer. 

When replacing the valve cover gaskets some have also found using Elring Curil T Liquid Gasket non-hardening, temperature-resistant sealing compound in conjunction with new gaskets seems to do a good job of resolving leaks.

An oil leak on the underside of the Varioram intake:
Another common source of an oil leak is from the underside

Underside of  the Varioram

of the intake manifold on the Varioram-equipped cars. Oil vapor from the crankcase/oil tank is vented to the intake of the engine, one of the very first emission control measures put on vehicles in the early 1960s and continues to this day. The intake manifold is metal and is a lot cooler in many cases than the oil vapor so it condenses onto the inside of the manifold before it can be ingested into the engine and burned off.

The condensed oil pools on the downward-facing surfaces inside the manifold. Located on the underside of the manifold is a lever that controls a Varioram valve inside the intake. The seal where it attaches to the manifold's bottom does not reliably seal it off and so a small amount of oil leaks out around it. Replacing the seal some would consider an expensive endeavor involving removing the manifold and disturbing several decades-old components that may introduce additional vacuum leaks for a very limited benefit. Although unlikely, some suggest that the leak can be the source of a small vacuum leak.

Let's face it our cars all have some level of vacuum leaks where the Motronic system can to some extent adjust for them and if really a problem operating symptoms would appear or even a misfire Check Engine Light would illuminate. For this reason, I would call a small oil leak here inherent in the design of the engine, and in the absence of other symptoms where it is verified as a contributing factor, no action should be taken. Sometimes a problem is only a problem because one keeps thinking of it as such.

Now for something completely different:

Here is an interesting posting I recently found on Rennlist:

"I [purchased] a 97 C4S that was leaking oil (chain boxes, base gaskets, etc) after basically sitting for 18 mos (~500 miles in 2 yrs). "Drove it every day for a month and voila...all but 1 of the oil leaks stopped"

 The above posting seems to suggest that just exercising an engine may cause leaks formed while standing for long periods to diminish if not resolve themselves completely

Oil Filler Bellows Removal – At this point, it is unlikely that the oil filling bellows is still nestled inside the engine oil filler neck on any 993. It originally was

Filler Bellows removed

designed to pull out making an oil fill easier. This bellows eventually breaks down and bits of plastic can fall down the filler tube into the engine oil. On most cars, this bellows was removed long ago. If you see it inside under the oil filler cap you can pull it out and throw it away. Unfortunately, if it is still in place once you pull it out, debris that remains will need to be flushed out and the oil changed.

Body fluids, Andy’s opinion:

Oil - I have always used Mobil 1. Although it is called synthetic technically it is not,

it is made from a petroleum base stock but it has been extensively processed to remove the bulk of the naturally occurring substances, paraffin wax, etc. that must be kept in solution by the additives to avoid sludge. I use Mobil 1 FS 0w-40 or FS X2 5W-50  with the slightly higher ZDDP level of 1100 PPM, as I have come to understand this additive reduces the scuffing of components in the valve train. I do not use racing or motorcycle oils that have very high levels of zinc, 1300~1850 PPM, as I understand, they may shorten the life of the catalytic converters.

Here is a page discussing how to read the oil-related gauges on a 993 and how it might influence the viscosity grade of oil you may choose to use.

What sold me on Mobil 1 oil was when I first used it on my 86’ Carrera. In Cleveland winters it would take twenty minutes or more for non-synthetic labeled multi-grade oil to warm up enough for the oil pressure gauge to not be pinned at its maximum 5 bar. When I filled the engine with Mobil 1 it took less than 60 seconds from dead cold as well below 32F to fall into the gauge's useful range. Most engine wear, I understand, happens at startup when an engine is not yet warm, the oil is thick and so does not properly lubricate. With Mobil 1 this period is much shorter as indicated by the oil pressure gauge. In retrospect, almost any oil labeled as fully synthetic will likely result in similar behavior.  As a plus, Mobil 1 in the grades needed for a 993 can be ordered online for pickup at Walmart, which works for me. Two 5-gallon jugs cost about $50. Then again has anyone, who does not track their car, ever seen a “catastrophic oil-related engine failure” as fear mongered in oil advertisements? If one changes their oil regularly with the OE-recommended brands and viscosities, probably not.

Here is a Porsche USA Training Center video about oil:
https://993servicerepair.blogspot.com/2023/01/how-to-keep-your-porsche-engine-running.html

Then Again... Here is what Blackstone Labs, the folks who actually test oils for engine wear say on their website:
"You can go into any mass retailer (Wal-Mart, Meijer, AutoZone, etc.) and buy a 5W/30 (or any other grade) that will perform well in your engine. One of the best-kept secrets of the oil industry is that these store brands are actually the same, quality oils that are produced by the major oil companies. The only difference between these products and the major company brands is the name on the container and the price. Don’t believe us? Try running your own experiment: do a sample on Oil A after a known number of miles, then do a sample on Oil B and compare the wear levels. You may see a little fluctuation, but it’s very rare for one oil to make a significant difference in an engine’s wear patterns."

Quoted from: https://www.blackstone-labs.com/which-oil-to-use/

Porshe Classic branded motor oil:

Lately, Porsche has begun marketing  "Porsche Classic" branded motor oil. To be clear Porsche doesn't make motor oil. Porsche is just private branding oil just like auto parts chain stores do. The only difference is that at auto parts stores private branding is part of a lower price point strategy whereas with Porsche it is part of a premium price strategy.

The specifications of motor oil regardless of price strategy are so tightly controlled that branding is not much of an indicator of how one brand over another influences the durability of the engine. As discussed above I use  Mobil 1, not because of the brand but because it is readily available, with promotion not expensive and they publish detailed information about each oil they sell such as zinc levels, one of few formulae features that can actually enhance how the oil contributes to engine durability in our cars. I am sure other manufacturers' brands publish this same information if one does a little research and is comparable to Mobil 1.

Fuel  Injector & Fuel System Cleaner - I am standing on thin ice as I have only anecdotal support of my opinion concerning this subject.

I hear of issues with clogged fuel injectors and the need to remove and service or replace them from time to time among 993 owners. I have had two electronically fuel-injected Carreras. For the first one, I drove 150K miles without a fuel-related problem. My current 993 has never exhibited an injector problem. I attribute this to treating the engines twice a year with two consecutive tanks of gas where I added Chevron’s Techron fuel system cleaner. My understanding is that Techron, unlike competitive products, will not produce burnt by-product solids as competitive products can if used in high concentrations. Also, Techron is part of the standard additive package used in Shell-branded gasoline and when added in addition to the detergent already present in the fuel helps to remove stubborn carbon deposits. Tests have shown that it takes more than one treated tank of gas with added Techron to make a visible difference in the accumulated burnt fuel byproducts in the engine.  As a side note adding this stuff to a hard-to-start Weed Wacker does the trick every time!

Manual Transmission Gear Lubricants:
The additive package used in gear lubricant is specific and serves several related purposes. In normal operation, the sulfur/phosphorous additive forms a black sacrificial

coating on the steel gears. As the gears turn, instead of wearing the steel, the sacrificial coating of additives is peeled off or worn off. This is normal and acceptable in all steel gears. This is why after a very few miles gear lubricant in our cars turns black and this is not an indication that it needs to be changed. Gear lubricants are produced to specifications the major classes are GL-4 and GL-5. These specifications are not the sole indicator as to how well they work with the synchronizers, metallurgy, or wear characteristics in our car's transmissions. For this reason, always use a brand and grade of lubricant tested and recommended by Porsche or a transmission expert who works extensively with the Getrag G50 Varient synchromesh transmission found in the late-'80s-911/964/993. Be aware these recommendations change over time so look for the latest information before just refreshing your gearbox with its previously filled brand and type of gear oil.

Why are the synchro teeth rings in our transmissions non-ferrous? This may have to do with the gear oil. If they were steel (ferrous metal) the additives in the oil over time would build up a coating and alter their friction properties altering shifting feel and potentially shifting acceptability. The buildup of a coating from the gear oil additives is not a primary concern for a track car as the transmission is opened up and serviced more often than on a street-driven car. For racing applications steel synchro rings are used, in part, for the racing synchro teeth geometry that provides a stronger positive lock when shifted into each gear. A useful feature under extreme racing conditions but something that can contribute to less than smooth shifting in a street-driven car. 

When my transmission was last serviced it became apparent that there was really no wear to be concerned about on the ring teeth anyway. The issue was the loss of the textured facing on the synchro's toothed rings friction facing that engages against a counterpart cone to form the synchro clutch. With wear, the synchro's clutches' facings eventually wear down and do not provide adequate friction to cause gear synchronization and present as gear grinding during shifting.

Here is what the factory says about the gear lubricant change interval:

Here is a page discussing shifter feel as our cars age.

Here is an extensive discussion of gear lubricants you may find interesting.

Some folks change their transmission's gear oil DIY. The cardinal rule to changing the lubricant is to crack open the fill port high on the transmission first before draining the lubricant through the lower drain port. This is to avoid a situation where the oil has been drained and subsequently the filling port is frozen shut resulting in one being stranded with a transmission emptied of lubricant.

Gasoline Octane:

 So long as you use fuel with an octane rating as specified in your owner's manual or higher you are good to go, using fuel with an Octane rating higher than needed will

work as well but is an unnecessary expense. Some folks like to use racing fuels that in some cases have very high Octane ratings. The benefit of these fuels is they generally do not contain any methanol as is typically mixed into pump gas sold in the continental United States. Methanol is referred to as hygroscopic in that it attracts and retains moisture. Over time this moisture will attack the metal components of the fuel system and may contribute to the development of sludge in the fuel system. For daily driver cars this is not an issue but if your car spends a good bit of its life in storage consider a methanol-free fuel, either racing gas or a listing of stations that offer methanol-free pump gas is available through a quick search of the internet.

Fueling-Up Smells: 

With a 993 "topping off" the gas after the first forced pump nozzle

click-off will splash fuel in all sorts of places it shouldn't go both in the filling port drain and the gas tank venting system. The overflow gas fumes can persist even after the volume of fuel in the tank has drawn down. 

If you have inadvertently overfilled the gas and are experiencing fuel fumes run your car so the fuel gauge is somewhere below pinned on full. Then park your car with the frunk open and the lower hood latch pushed in manually with a screwdriver until it snaps into the closed position. This will shut off the frunk light and save from running the battery down. Then let the car sit for several hours in a well-ventilated space to evaporate the vapors. When the vapors have subsided pull the hood latch lever to snap the latch into the open position so it can receive the hood upper latch when closing the lid. 

If this does not seem to resolve your issue there can be a leak in the filler neck or one of the hoses attached to the gas tank. This is not a common issue however Porsche has published a Technical Service Bulletin TSB9401 (2007) covering replacing the filler neck.

Andy

If you found this page informative return to the main page and bookmark it for future 993-related servicing, repair, and upgrading guidance & information. If it saved you some time, aggravation or even some coin consider a donation through the button on the top left margin of this page.

#Transmission Fluid #Gearbox oil #Gearbox lubricant #gear box  #fuel #odors #leak

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Porsche 993 & 964 Resource Notes & Words of Wisdom Page

This page contains resource notes beyond the over 100 other 993 buying, servicing, repair, and upgrade topics in this blog that just make owning, servicing, and getting parts for a 993 or 964 easier and less costly. It is a work in progress and will have entries added going forward so check back here from time to time.

CD-ROM or download .pdf Porsche Parts Catalog:

 The 993 & 964 CD-ROM parts catalogs are in some respects a re-part numbered appendix to earlier model catalogs. For this reason many smaller subassembly part numbers are just plain missing. For example, the broken-out component list for the rubber shift coupler is listed in an earlier catalog with inexpensive part numbers for purchase where only the entire assembly, an expensive part is listed on the 993 CD-ROM.

Shift Coupler

Another example is the BOSCH distributor that shares many of the same parts as earlier single head designs. The drive gear, seal, and shear-pin needed to service the internal belt on a 993/964 distributor is listed for the single head BOSCH distributor in the '80s Carrera catalog these parts are most likely completely interchangeable.

Another example is the listing of electrical harness replacement plugs, sockets and other terminations most of which can be found in a setion of the 964 catalog listed at the bottom of this page. and not to be found in the 993 catalog.

 The Factory 993 Parts Catalog and its earlier Model iterations can be found online with a little searching.

For example: 

 https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/

  

The Factory Shop Manual in binders or as a .pdf:

Similar to this the Porsche Factory Shop Manuals for the 993 & 964 act in many ways as an appendix to earlier 911 shop manuals and is missing entire subject areas covered in depth in earlier model shop manuals. For example, the sunroof mechanism design goes way back to very early cars. An early-year shop manual has a complete section on the disassembly, adjustment, servicing, and reassembly of the sunroof. This is not to be found anywhere in the newer  model shop manuals. This page includes some select sections from ealier shop manuals that apply to the 993 & 964.

The factory shop manual and its earlier 911 model iterations can be found online with a little searching: 

For example :https://www.carpdfmanual.com/porsche/ 

Items that save a lot of aggravation while owning and servicing your 993 or 964:

• 

  
  

  A long-reach low-profile hydraulic floor jack, similar to what is sold at Harbor freight, is something you will bless the day you purchased it every time you change your oil or do most any wheel end or under-car servicing.
  
• Porsche specifies that the 993 be only lifted by the factory jack points to do this with jack stands involves subjecting the car to significant twisting forces when lifting from a single jack point, say when servicing a wheel end.  Using a product called LiftBars in conjunction with the two jacking points on each side of the car eliminates this twisting force and is discussed in the middle of this page.
• 

• 
  A pressure bleeder for when changing the brake fluid. Something I found to be a golden item to have on hand making one-man brake bleeds a no-brainer.

• The Original Equipment Emergency Jack, the jack that comes with the 993 Carrera is compact, lightweight, and extremely unsafe to use on the side of the road. 

  

  Original Carrera
  Emergency Jack

  Swapping it out with a  light alloy scissors-style Porsche branded jack that came with the Turbo is an option. It is referenced under several Porsche part numbers for example; 000.721.711.05 or 996.721.711.00. It can be purchased new at the dealer, from Pelican Parts, or used on eBay or from a Porsche dismantler. It seems this jack has been renumbered and superseded several times in the catalog so if you purchase it without seeing the actual jack have the seller verify the jack is the scissors type with the 993 alignment stud for the 993 body lift points.
• An inexpensive steel scissors jack from Walmart, Amazon, or really most auto parts stores is an option. In this case, one will need to modify the jack by adding a  short bolt with washers and nuts forming a stud that interlocks with the hole on the lift point of a 964/993. This modification is very important as it protects the car from slipping off the jack during an emergency jacking event.

Porsche Scissors
Emergency Jack

Generic Scissors Jack with
nut, bolt & washers stud added

• A 1.5 to 2.5 Amp float/charger that fits into your cigarette lighter or one with an adapter cord that does. A lifesaver if you left your lights on and your car won't start. Plug it in and 4 hours later your 993 will start right up.
• A basic $50~$100 On-Board Diagnostic (OBD) reader such as an Autel AL519 handheld reader or even an advanced one that can read the Porsche Specific manufacturer codes and running data. Something very useful when sorting out why the Check Engine Light is lit on your dash. 

With the basic reader and even if you have no intention of ever servicing your own vehicle reading out the trouble codes is as easy as using a pocket calculator and a quick Google search will tell you what the codes mean and what various folks did to clear them and the attendant Check Engine Light. This alone is very valuable for when you visit your local servicing entity you will know if the remedy they propose makes sense avoiding unnecessary work or upselling.  More on this subject here.

• A .pdf copy of the Porsche 993 & 964 parts catalogs, discussed above.

Parts & Information one should always have on hand in their 993/964:

• A complete set of  the three belts for the alternator/fan/AC compressor; 
• Three spare pulley capscrews (

  900.976.004.01) 

  & 
  

  

  Compressor Nut

• Three AC compressor square mounting nuts (964.126.311.00); 
• Consider keeping all the individual tools to replace the belts stored in the frunk. Belts can break without warning on a,993, especially if not tensioned using a gauge and you may end up not having a  servicing shop along the road to replace the belts, having this stuff on hand will get you back on the road without drama. Here is a resource to help in identifying these items;

The two biggies! Always have a backup; 

• A 993 or 964 DME Relay (

  993.615.227.02 for the 993)

   A failed DME relay is the number one reason by far that folks get stranded when their  993 won't start.
• Window switch (

  964.613.621.01)

   in one of your door pockets. The window switch is so one doesn't find one's self out in the rain with a window that can't be rolled up. Also, be aware there are two switches for the passenger side window that are linked together and after swapping one out you may find the offending switch was the other one on the other door. 

  

  DME Relay

• Key stalk, cut for your car in your wallet, and an extra 
• Electronic fob, if your car came equipped with one, in the frunk with a fresh battery. If you lose your key or your fob fails this will save you from what will at least be an overnight stranding to get a replacement. 

• Keep a printed-out copy of the 993 fob programming instructions including your immobilizer code in your owner's manual in the frunk. This, in a pinch, will allow you to start your car even if no electronic fob is available. This does not supersede keeping a working spare fob in your frunk as well. Fumbling through an unfamiliar procedure for the first time in some parking lot can be a real challenge potentially drawing the interest of a local police cruiser. Also, the programming process can be problematic for some to complete due to problems with electrical noise internal to the ignition switch or other reasons and you don't want to find out you can't start your car due to a faulty fob while away from home.
• If one has only one working remote entry fob it is asking to get stranded. The dealer-supplied fob has gotten astronomically expensive however, a direct replacement aftermarket fob for the 993  is available through Specialized ECU Repair or EZ IMMO BLOCK . Be sure to order the 315Mhz one for all USA-delivered cars 1995-1998 or the 433Mhz one compatible with cars originally delivered in Europe with the same Drive-Block alarm/immobilizer system. There are a few exceptions to this rule, for example, Australia-delivered cars and certain early production vehicles so look at your fob's FCC license label or look up the part number in the Porsche parts catalog to verify which of the two will be compatible with your car. 

The Specialized ECU Repair and the EZ IMMO BLOCK fobs use a modern button battery, whereas the OE fob's canister battery /contact arrangement has proven to not be perfectly reliable. I have been carrying around and using the above aftermarket fobs as daily users for several months now where they are exposed to moisture and lint in my jeans pocket and have proven to be 100% reliable to this point.

EZ IMMO BLOCK also offers a new fob that can be used to clone its configuration from any working fob. avoiding the factory programming sequence some find difficult to complete. Here is a page that discusses programming fobs, mating them to one's 993. 

• This is sort of an odd item, get rid of the one anti-theft wheel nut on each of your wheels. Replace all four of them with a fresh standard nut purchased online or from the dealer. The original keyed security nut is prone to stripping and failing. When this happens you can get stranded at the side of the road with a flat tire that you are unable to change. Besides few, if any of our car's wheels are stolen these days as the 993/964 have been around long enough that used wheels are cheap and plentiful to buy on eBay vs stealing them off of your car. Also if a professional thief wanted your wheels any wheel security nuts are just a minor nuisance.

• Here is a comprehensive discussion of junk you should consider having in your frunk.

Porsche branded, Porsche's OE Supplier branded, and generic aftermarket branded parts:

There seems to be a lot of confusion as to the relationship of quality (durability) to a brand. For example, durability differences between Porsche branded premium priced parts versus Original Equipment manufacturer (OE) supplier branded, like BOSCH versus third party branded parts, such as URO when purchasing replacement parts for our cars.

Keep in mind the below definition of Premium Pricing as you read on: 

"Premium pricing is a strategy that involves tactically pricing your company's product higher than your immediate competition. The purpose of pricing your product at a premium is to cultivate a perception in the market of your product being just that bit higher in quality than the rest."

First of all common service parts such as rotors, pads, struts, links etc were never designed or manufactured by Porsche to begin with. Their design, testing and manufacturing was left to Porsche's tier-one suppliers, Sachs, Bosch, Marinelli and others. So buying the Premium Priced product in a Porsche branded box at a 40% or more premium price vs buying it in the original manufacturer's branded box represents a poor value. Bosch makes fuel injectors, oxygen sensors and every component of the Motronic engine management system, Porsche never did. 

The reason why dealers prefer to sell parts purchased through the Porsche distribution network is that they are mostly used in in-warrenty work where the published retail price is not relevant and the captive financial relationship between the dealer and the parts source is, how should I say, a lot less than arms length. Also higher Premium prices improves margins on out-of-warrenty work for customers who believe servicing should be done at a dealer.  

Having higher Premium aftermarket retail parts prices is also attractive to the dealer's Independent (jobber) import car servicing customers because the higher retail price translates into higher margins when sold to you as part of a repair. In essence folks who buy parts to service their vehicles on their own (Do It Yourself) are simply not the dealer's core parts customer and for this reason dealer pricing seems, many times, to be irrationally high to the DIY folks. 

It is interesting that the margines are so good on retail dealer parts and labor that an entire industry of independent service contract/extended warrenty providers has sprung up making good money by negotiating reduced pricing on dealer parts & service. These are the same folks that have your cell phone on speed-dial that are constatly phoning you about your expired new-car warrenty, go figure?

Parts sold through the dealer network or independent distributor are referred to as Service New parts. Universally, they are not subjected to the same level of quality control as the same part supplied to Porsche at car assembly. Most testing is driven by warranty periods. Many Service New parts have been through what is euphemistically called a "Quality" program to take manufacturing cost out of the part while still being durable enough to survive the reduced aftermarket warrenty period.  

Aftermarket parts warranties, through the dealer or a distributor generally don't come close to those offered with the car when it was new so many of the now down graded parts simply don't last as long. This is especially true when a part has long been absent from a current production vehicle, in many cases its manufacturing has been handed off to a lower-cost, low volume manufacturer as most parts on a 993 or 964 now are. In a way, there is a perverse incentive in the entire aftermarket parts industry to make Service New parts less durable resulting in the opertunity to sell them to you more than once. 

Porsche sources its aftermarket Service New dealer parts from the same manufacturers used by independent import parts distributors, referred to in the industry as Warehouse Distributors. So the same part, of the same quality in most cases, came off the same assembly line with the same quality controls regardless of who's box it is in. This is particulary true for parts where the current manufacturer originaly supplied the part to Porsche at assembly.

Porsche branded vs original manufacturer branded tie rod end

 Sometimes there is no attempt made to hide who made the part 

as here is what appears to be a co-branded oil filter that came in a Porsche box but is clearly made by MAHLE:

Certain parts are an exception to this rule. 

Performance Market parts: 

Those supplied by by botique high performance parts distributors, for examle some of the items offered by StopTech who cater to those who race their cars or like the idea of installing race inspired parts on their car. They are usually limited to wheel end and suspension components and clutch & engine enhancements. These parts usually include cosmetic or functional enhancements and can have durability the same as or even better than run of the mill Service New part.

 

Low-Value, Low-Tech parts: 

 Some parts are manufactured by multiple entities under differing conditions at times using different designs of varying quality/(durability). They are usually low value. low-tech, easy to manufacture higher volume parts. 

For example, the window switches in a 993/964 if manufactured in Germany or Eastern Europe are similar in design to the original factory-supplied part. The same part purchased under the URO brand and now even the Porsche branded part manufactured in Taiwan, although they look very similar, are an entirely different design internally and suffers functionalproblems that become apparent when attached in series to a second switch as is done for the passenger side window with switches on each door. So, for small incidental parts be observant of the manufacturer as printed on the actual part and/or its country of origin unrelated to what branded box it came in. The original switches supplied with our cars typically last 15 years or more and for the DIY inclined can actually be repaired and stored in one of the car's door pockets for emergency use.

As an experiment I recently researched where 993 Porsche branded verses manufacturer branded windshield glass comes from for a 993.

It turns out this is easy to do because to be sold in the US automotive glass must be labeled with a US DOT number that identifies the specific factory of origin and also the country of origin. Turns out Porsche branded glass with the Triangle-P logo comes from the same two factories in Germany as all aftermarket windshields for our cars. The only difference is the added Porsche branded logo on the Porsche dealer sold glass. So any premium price one pays for the dealer part is purely to get the logo.

Hunting for the best value in Service New replacement parts:

Many times a part will seem to be a "Dealer Only" part because the original manufacturer's part number is difficult to obtain. Many online auto parts distributors list multiple part number cross-references for a part that can be looked up and may result in a less expensive source of supply. Also, many times the original manufacturer's part number is actually printed on the part and when searching for a part using that number may result in a significantly lower cost source of supply.

For example;

The Denso supplied sensor blower part on the back of the

Climate Control Unit (CCU) discussed in the "What is that buzzing behind the dash?" section on this page. When looking at the part the original manufacturers part number is printed right on it.  Where conducting an internet search under the Denso "173000" and excluding the car make extension -0410 it turns up several inexpensive alternative automotive branded part numbers in the $50-$75 range versus the Porsche dealer part that is several hundred dollars. The alternate part number may come with a different mounting frame however the frame and, if needed, the electricl plug can be harvested from your original unit.

 Another example is when a part is only available at a lower price through a dealer,

just not a Porsche dealer. For example the vacuum actuators on the Varioram intake manifold, Porsche part number is 99311046202 discussed on this page. On the part is printed the supplier Pierberg's part number 7.14242.07, see the picture to the right. This number crosses to the BMW part number 11617786961. This part if purchased under the Porsche part number is $103 under the BMW part number it is $46. There are three of these on the Varioram manifold so the savings adds up rather quickly. This cross was discoverd by reading the manufactuer's part number off 

the part in a picture at a distributor's web site and then searching

for a cross on an internet distributor's part number lookup.

Remanufactured Parts:

Remanufactured parts such as alternators, starters & calipers are highly variable in the quality (durability) of the finished product. First of all the condition of the used part from which the rebuilt part is finished out has a big impact on part quality. The used part is referred to as a "core" in the industry and the remanufacturer really has no control over the condition of the cores he receives. 

Each remanufacturer has their own standards for an acceptable core. In all cases, the standards doesn't in any way approach that of the new part when it was installed on your car at assembly. This is why some reman calipers exhibit loose bleeder screw casting threads that strip right out of the box. Also, a reman core may have been installed, used, and through the remanufacturing process more than once due to some unidentified failing. A failing you are now installing on your car.

Once a core is in hand the remanufacturer decides what testing is done, what parts are replaced or reused. This also explains the wide variability of durability and short warranty on these parts. Reman alternators due to their complexity are an example where durability varies widely even from the same rebuilder.

The best way to get a reman part with potentially better durability is to always remove the part from your car and have that specific part rebuilt versus one purchased on-exchange made from the cores the rebuilder has on hand. This is extremely important on parts where the supplier has a very limited source of good quality cores or the core is a precision or a complex part to begin with. It also may minimize the risk of installing of a reman part that is not configured exactly as the originally installed part. See this page for how this can be an issue.

In our cars the big one is the steering rack where rebuilder core availability is very low, core quality is just plain bad and the one recently taken from service from your car is the best bet for a durable remanufactured part hands down. Also when working with a rebuilder directly you can discuss the rebuilding process and what sub assembly parts you require to be refreshed. This is very important in the case of alternators. Luckily there usually is an electric motor/alternator/starter rebuilder with knowlegable service counter men in most cities of any size to do the work on your original component. If you have the interest here is a DIY on how to remove and reinstall a 993 steering rack.

Here is a page that lists my favorite go-to pages for parts for my 993 and also for a 964 information and parts supply. 

The difference between 964 and early 993 1994-1995 Non-Varioram OBD-1 vs. and a 1996-1998 Varioram OBD-2 Carrera

OBD-I vs OBD-II

The 1995 and early 993 and the 964 OBD-I cars have a single oxygen sensor located before the catalytic converter (CAT) that is used to evaluate and adjust the engine to optimize performance while minimizing emissions. It captures data only on the exhaust emanating from the engine that can trigger a Check Engine Light (CEL), not the downstream emission components. Since it has only one oxygen sensor before the CAT it does not evaluate the effectiveness of either cylinder bank of the engine individually or downstream components such as the catalytic converters nor does it evaluate the performance of the Supplemental Air Injection system (SAI) at start-up. For these reasons, it reports fewer issues that will trigger a CEL and so will have fewer issues that will cause it to fail a state emission inspection. To identify a car as an OBD-I vehicle look under the rear bumper at the rear center of the engine one will see a single oxygen sensor screwed into the catalytic converter hanging down in a protective shroud as seen below.

Location of the oxygen sensor on an OBD-1 equipped car.

The 1996 and newer 993  OBD-II car has four oxygen sensors located before and after each catalytic converter segment these are used to evaluate and optimize the performance of the engine, the catalytic converter (CAT), and the air injection system. Since it has two before CAT and two after CAT  oxygen sensors it evaluates the performance of the catalytic converters as free-standing devices and the performance of the supplemental air injection system at start-up. For these reasons it reports a greater number of issues that will trigger a CEL and so more issues that will cause it to fail a state emissions inspection in most states. 

The key service issue with the later 993 is that the emission OBD monitoring system will capture:

• The SAI air pump's electrical supply wires have insulation that fails from heat exposure. Getting to the wires to repair them is not easy with the engine in the car and so they should be addressed if the engine is removed from the vehicle for other service reasons. The pump itself is a very expensive part and rarely fails as it only runs for a few moments at the startup of an engine from dead cold. For this reason, if your shop suggests the pump needs to be replaced due to a Diagnostic Trouble Code you may want to prevail upon them to just replace the pigtail wires leading to the blower motor.
• The SAI system has a check valve that can throw an OBD-II code as it has a relatively short service life due to internal corrosion and should be replaced every two to four years.
• The SAI ports to the exhaust path can clog throwing an OBD-II code. This is the biggest gripe with the OBD-II vs the OBD-I car by owners. The most cost-effective method to clear the clogs is to remove the exhaust manifold and snake the ports out with a wire, This known issue has caused a debate in the 993 community as to its cause being; 

• The overfilling of the oil; 
• Leaking of oil around the valve guides or; 
• Both. 

Although the prevalence and to the extent each contributes to the issue is still open to debate generally, once the ports are cleared and the check valve replaced this cause of a CEL seems to not return. 

Here is a little more information on the subject of the Air Injector system's known issues including the above: Emission Control Systems - The Horror of the Check Engine Light!

964 & 1994-1995 993 Non-Varioram vs. 1996-1998 Varioram

To be clear owners of the earlier non-Varioram and owners of Varioram cars are generally happy with the performance of their vehicles. The Varioram cars breathe a little easier. The theory, I understand, is much like the valves on a trumpet where changing the air path lengths changes the frequency at which the instrument wants to oscillate. The Variorum system changes the effective length of the intake manifold runners so the air intake pulses maximize cylinder intake air charging at specific RPM ranges. This in conjunction with the larger intake valves produces slightly higher torque and horsepower at certain points along the rpm range. The varioram car is identified by a large bright cast metal intake manifold sitting over the top of the engine, see below.

Location of the Varioram intake manifold on cars so equipped.

The Varioram concept was originally implemented for the 993 in the Carrera RS as a way of increasing performance and was later added to the standard normally aspirated engine. The performance enhancement is small and incremental. On the negative side, there are more vacuum actuators on the engine to actuate the valves in the intake manifold and by now they are all suspect and should be tested for leaks in their internal diaphragms, The testing procedure is in the middle of this page. 

Model Year and DME differences, my understanding is that:

• MY 1995 and earlier 993/964 OBD-1 BOSCH Digital Motor Electronics (DME) Electronic Control Unit (ECU); 
• Its simpler intake manifold is better suited to certain intake modifications such as adding a supercharger. 
• It tests fewer emission issues and so reports fewer Check Engine Light (CEL) events.
• The 993 1996 OBD-II BOSCH DME ECU;
• BOSCH ECU Panumbersber ending in 008 (Carrera) and 758 (Turbo) in the US market.
• Unique, being the first model year where OBD-II regulations were implemented and; 
• Can not, as originally configured, have its memory reflashed to alter its intake maps.
• It can be internally modified by adding a daughter board to allow for reprogramming by Specialized ECU Repair at  https://www.ecudoctors.com/. See my comments on the advisability of doing this in the "Gotcha" section below.
• It also does not report the five non-continuous tests' individual emissions-related OBD Readiness statuses as they flip from "Not Ready" to "Pass" or "Fail", just reporting the individual results when all the tests are complete. More information on what readiness tests are can be found here;
• All readiness tests must be completed in a single-engine running event or all tests revert to a not-ready state and the drive cycle will need to be repeated. This may be why some owners of these early OBD-II cars experience frustration getting all the flags to a "PASS" state for an emission inspection after having their battery disconnected for service or replacement.
• The  993 1997- forward OBD-II BOSCH DME ECU; 
• BOSCH ECU Part numbers ending in 649 (Carrera) and 377 (Turbo) in the US market.
• Can, as originally configured, have its memory reflashed to alter its intake maps. See my comments on the advisability of doing this in the "Gotcha" section below.
• These cars report the status of the five readiness statuses individually for each non-continuous test as they are completed and retain this information even if the ignition is turned off before all the tests are complete. More on readiness tests and OBD reporting can be found here.

993 & 964 "Gotcha" Common and sometimes ill-advised upgrades and servicing:

• 
  Installing a lightweight flywheel. I regularly see posts on cars exhibiting stall-out or excessive noise issues with this modification. A recent quote from Rennlist "The RS lightweight clutch and flywheel is great on the track, but a pain in the ass on the street." typifies the words on this modification. More on this topic can be found here. Also replacing the dual mass flywheel with one not implemented with this feature accounts for the "excessive noise" comment above. 
• 
  Upgrading to Porsche replacement radio with navigation. The screen is too small and the radio placement in the dash is too low to make it an effective replacement for your cell phone with Google Maps or Waze installed. An alternative to consider is a;
• Dash Clock Smart Phone Mount can be found on this page. 
• Alternative popular radio solutions can be found at the bottom of this page.

• Any modification to the Motronic ECU to defeat the Immobilizer or remap the engine ignition. All these modifications involve a vendor altering table values in a compiled program or "black boxing" what programmed functions
  
  in the ECU are and how and why they function. The remap only changes the performance envelope very slightly as the factory ignition maps are well optimized from the factory for performance using the readily available grades of pump gas at service stations. If one wants to address the immobilizer function here is how to do it without an invasive modification or reflash to the Motronic ECU.
• Servicing the Climate control unit (CCU). When having the CCU serviced by ECU doctors they swap out the original guts for
  
  their solution. The CCU controls or monitors 21 major functions related to the HVAC & the engine and is complex even by today's standards.  It is generally very robust and if you prefer to retain the original internals  others will service and repair your CCU if needed, including bergvillfx.com
• Swapping out the stock black calipers with 'Big Reds". A very expensive upgrade that offers no performance or brake-feel advantage for a street-driven car. Upgrades to consider are to be found here. 
  
  Better to just paint the faces of your existing calipers red like the souls on French-Egyptian fashion designer Christian Louboutin's shoes if you are looking for a fashion statement.
• Installing RS engine mounts. Many folks who installed them love them giving a more precise feel to shifting. Others have viewed them differently "the motor mount created an increase in vibration that just made a buzziness in the cabin. Things that never vibrated did a lot over 4k rpm." ("clib" a Rennlist member)
• Something called a "Top-End" rebuild on a 993, commonly proposed by an enterprising service shop but actually rarely needed,  more on this topic can be found here.
• Regearing the transmission to shorten up the gears. Although regearing
  
  can enhance the driving experience for some by moving the shift points to shorten the gears, it is an expensive modification. One may be better off learning to value the virtues of the stock, tall 2nd & 3d gears when driving in traffic.
• Having steel synchronizer rings installed in the transmission at servicing for a street-driven car may not be a good idea. First of all the steel racing synchro teeth geometry is designed to provide very strong positive gear locking for race applications so the shifter doesn't slip out of gear. This feature in a street-driven car is not relevant and makes for a significantly less than smooth shifting experience.  Having worn synchros replaced on my 993 I can tell you from observation it's not the synchro teeth that are subject to significant wear it's the friction surfaces. Gear lubricant GL-4/GL-5 attaches a sacrificial coating to the steel gears in the transmission so the coating wears instead of the gears. This property vastly increases the service life of the gears in the transmission. The standard synchros are a yellow brass or bronze alloy, a nonferrous metal, and impart smooth shifting. I suspect another reason why steel is not used in the standard rings may be how the brass gears interact with the gear lubricant differently than with steel over time.
• Swapping out the fan and alternator belts for a single belt arrangement. The factory belt arrangement seems to work just fine for street use and the belts have a reasonably long service life if the correct belts are used and are tensioned properly with a tensioning gauge. The aftermarket single belt arrangement is expensive to buy, and have installed and results in unintended consequences discussed here. The factory service manual recommends inspecting the standard V belts every 30K miles for retentioning or replacement. In practice, I would inspect the belts every 15K miles and just replace them every 30K, one of the inexpensive and easier DIY servicing items.
• Shy away from any exhaust updates that involve removing or replacing the factory Catalytic Converter. Do you plan to drive the car legally from an emissions standpoint? If so consider modifications after the CAT(s) only. There are lots of options.
  
  Any comprehensive exhaust change only improves engine performance very little, if at all, and the weight saving is probably only material if one races their car. This is not to say thoughtful aftermarket muffler modifications downstream of the CAT(s) such as those done by Fister or others don't enhance the symphony the engine produces. 

In any event, save all the original exhaust parts as when the car is sold finding replacement parts to put back may be problematic and expensive. In the case of the stock CAT the value of the internal Platinum/Pladium catalyst compounds have skyrocketed as of late and the used converters in older cars such as ours contain a lot of it where the street value for the internal catayst alone is aproaching $1000. For this reason , I suspect a lot of the take-off ones will be chopped up for their content. This may, in a few years, make finding a good functional used one at a reasonable price a problem.

• Swapping out suspension or brake components for ones intended for race applications. For example, non-DOT brake hoses with non-crimped terminations are a brake failure waiting to happen unless you are prepared to inspect the lines after every few hours of operation as is done with race cars. 

Another is swapping out the cast suspension arms for adjustable race arms such as those sold by Tarett and others. Again these features being easily adjusted for race applications also make them easy to go out of adjustment for street applications.

Finally replacing rubber suspension components for harder resin or metal such as bushings and strut hats. These transmit noise and vibration to the car and in some cases have been implicated in sudden glass failure when used on a street-driven car. If your car is being developed as a track weapon, go for it, otherwise, I would shy away from these sorts of upgrades.

• Adding wheel spacers to push the tires out closer to the edge of the wheel well. I view this as a case where someone is overruling function for fashion. Doing this diminishes the available tire travel without the wheels rubbing the wheel well liners. this can be a problem on public roads. Also, the use of wheel spacers increases cantilever forces on the wheel-end suspension components. In some cases, it will require replacing the wheel studs.
• This is not a don't-do, more of a consideration. When changing out components such as the radio head, suspension springs or other major components keep the originals as having them is important to some buyers when you go to sell your car.
• Getting one's 993 wrapped. This is a common enthusiast discussion Item. Don't do it! The manufacturers of the film 3M & others openly admit it has a shelf life of two years. If you ever decide to remove it several years from now, after it has dried out, be ready for a job similar to removing the stone guards from your car, but on a much larger scale. Some have experienced paint pulling off with the film, a real nightmare. Also see this page: Fender Guards, Body Wraps
• Swapping out the factory wheels for larger diameters up to
  
  18-inch original option wheels or even larger aftermarket wheels used in conjunction with very low-profile tires have become a fashion statement of late. Larger wheels are really not the right thing for the vast majority of drivers. For street use 17" wheels are somewhat harsh on a 993/964, and optional 18" 993 wheels can be downright jarring. For years 15" to 16" were standard on the 911 and gave a reasonably compliant ride. For proper suspension geometry on the  993/964, the total diameter with rubber-mounted are all the same regardless of wheel size, just the height of the tire wall gets shorter as the wheels get bigger. 

A taller tire in conjunction with a smaller diameter wheel gives you some tire tread roll-over feel as you get near the edge of the tires' grip in aggressive turning

16" vs, 18" Wheel

while driving.  Roll-over is a feeling in the steering as the front tires begin to displace horizontally and the edge of the tires begins to distort or roll-over. In my experience the 18" low profile tire gives almost no warning before letting go and sliding, 19" probably no warning at all. For nonprofessional drivers, the margin of safety given by the roll-over tread steering feedback provided by smaller rims with higher profile tires before sliding is a welcome and significant safety communication. 

Finally if one peruses the catalog of documents in this blog via the list found in the top left-hand column of this document (when viewed on a desktop or laptop computer) it will provide somewhat comprehensive education on the workings, servicing, and upgrading of a Porsche 993 and many subjects that also apply to the 964. 

If you found this page informative return to the main page and bookmark it for future 993-related servicing, repair, and upgrading guidance & information. If it saved you some coin consider a donation through the button on the top left margin of this page.

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