Insidious Poor Running or Power Robbing issues

Cleaning the Idle Control Valve (ICV) – The idle control valve has proven to be very robust and almost never needs to be replaced. However, it does get dirty causing it to not function properly and should be cleaned every 30K miles or so. If the engine seems to idle roughly or at too high a speed just spray it out with carb & choke cleaner until the valve internals look clean of carbon deposits and its internal rocker rocks back and forth with a spring-suspended wobbling action when you gently rotate the unit’s body in your hand. The valve is located on top of the engine in the center close to or slightly under the engine compartment insulating blanket. It is held in place by the hoses that are attached to it. On the Varioram cars, it also has a grommet that holds its body to the metal manifold casting that can be a small challenge to put back in position. 

Dirty Valve

When cleaning my car’s valve I use Carb & Choke petroleum-based solvent cleaner. I also clean the electrical plug and socket with CRC QD electronic cleaner spray as carb & choke cleaner is not intended for plastic electrical connectors. Be sure the electrical sockets dust boot grommet is fully seated in the bottom of the electrical socket so the plug fully seats when reconnected. 

When powered with the ignition on the valve vibrates and may buzz a little informing one of its operation. No vibration and it is not working.

Cleaned Valve

 It can be disconnected from the wiring harness and tested with a 9-volt transistor radio battery once cleaned by powering its electrical connector pins with it. Applying voltage to the center & one of the side pins will cause the valve's internal rocker to move in one direction; applying power to the center pin and then the other side pin will cause it to move in the other direction.

ICV Ele.
Connection

For future reference one can write the date and miles once cleaned right on the valve housing, using a felt-tip Sharpie pen. I tend to mark this information when replacing or servicing ancillary items whenever possible. For routine items such as rotors, caps, and oil changes I make a felt pen note on the underside of the engine lid and clean it off and update it with new information when I revisit the procedure.


Cleaning the airflow sensor - if not done in the last 60K miles or so.

It must be cleaned with a Q-tip in conjunction with “CRC Mass Air Flow Sensor Cleaner” just spraying it out will not always release the grey debris coating that has accumulated on the sensor element, the element when clean looks like a white circuit board with visible components on it. See Appendix “M” “Mass Air Flow Sensor MAF Cleaning does it work?”.  If the sensor is throwing an OBD Code or is suspect for other reasons and the sensor element looks clean, cleaning it will not improve its functionality, it may just need to be replaced. Also see the section titled " The mercurial fuel delivery system in a 993 engine, " at the bottom of this page

Fixing insidious, power-robbing, vacuum leaks – When one of the vacuum actuators, three on the non-Varioram and five on Varioram Cars, or any of the rubber hose connectors fail (leaks) or slips off the intake on a Varioram car will not work properly cutting power. This can also cause a rather large vacuum leak and may influence the availability of vacuum when actuated, vacuum needed for other functions related to the engine to work properly. 

I checked one of the now 23 Plus-year-old diaphragm style actuators by disconnecting it, attaching a short length of vacuum hose to it, and sucking on the hose by mouth, lots of air drawn, but no movement. Interestingly what seemed to be a rather large vacuum leak through the actuator did not throw an OBD code on my car. 

I ordered three 993.110.462.02,  and one 993.110.461.03 for my Varioram equipped engine:

• One for on the top left side of the engine intake manifold; 
• One that is part of the HVAC system and is connected to the lower left engine compartment heater blower ductwork; 
• One on the left side underneath the Varioram intake manifold, and; 
• The fourth actuator is on the top right side of the intake manifold, similar to the others but with a longer actuating arm.

The aftermarket replacement actuators from the dealer seem to have their diaphragm made of silicone rubber and so should be much more durable than the originals installed on the engine.

A fifth actuator that can cause a power loss is located behind the Climate Control Unit (CCU) in the dash connected to a ventilation flap. This actuator is not present or may be present but disabled on early production 1995 model year and earlier cars.

The actuator is a piston-style one and looks to be rather robust. Porsche sells it as a complete vent unit but I bet, if leaking, an inexpensive metal can-style actuator purchased on eBay could be MacGyvered to replace it at a low cost. I tested mine by pulling the CCU clear of the dash w/o disconnecting the CCU harness then attaching a hose directly to the actuator and drawing a vacuum by mouth. Once a static vacuum was applied its pushrod stayed retracted so I could infer that it was not leaking. Interestingly the actuator’s pushrod had become detached from the vent mechanism, a very common situation. I replaced the missing pin with a tie wrap, which is probably good for at least another five years. Once reconnected to its vacuum source, I started the engine and actuated the vent flap by pressing the recirculating air button on the CCU while observing it through the dash hole. I then buttoned things up and was good to go, taking all of ten minutes. 

Some early MY1995 and earlier cars do not use this actuator behind the CCU so the actuator is not present or if present the plastic lever attaching to the actuator's pushrod is disconnected or missing altogether. If the actuator has no hose connecting it to an electrical control valve it is probably is of this earlier configuration.

It is quite easy to test the actuators including the  Varioram system on so-equipped cars, all the actuators, and the solenoid valves that control them you will need a helper:

1.       Have your helper  start the engine and run it for a few moments, to build a vacuum;

2.       Shuts the ignition off;

3.       Turns the ignition back on without starting the engine while you observe the engine;

4.       Observe  the three Varioram actuators on the engine going through initial cycling, you will need a flashlight and push down on the rubber duct attached to the fan housing to observe the third actuator underneath the intake manifold;

5.       For late build 1995 to 1998 cars with air conditioning press the air recirculate button on the Climate Control Unit(CCU) while the ignition is in the on position;

6.       Listen for the kerchunk sound of the vacuum-actuated recirculating air flap moving behind the dash; 1994 and early 1995 cars may not have this vacuum actuator present. If you do not hear the sound and are not sure if your car has the actuator function just pull the CCU partway out of the dash and look behind it with a flashlight for the little plastic barrel-shaped actuator. If not present your car does not have one if present but the arm attaching it to the vent mechanism is missing and the actuator has no hose attached to it your car has the updated vent mechanism that has been backdated with the actuator detached to work on your car without the actuator function.

7.       Go back behind the car and observe the heater flap actuator located on the ductwork on the lower left side of the engine;

8.       Cycle the CCU thermostat setting from cold to hot and back to cold a few times while observing the actuator;

9.       Observe the actuator retracting rotating the flap arm from the 7:00 o’clock (heat) to the 9:00 o’clock (cool air) positions as you rotate the knob on the CCU.

It is probably a good idea to run the above test any time you notice an operating change with the engine.

Improperly sequenced wires attached to the distributors:

If you recently had your car's distributor caps or ignition wires replaced at a servicing and are now experiencing poor uneven idling, loss of power, or what feels like an occasional backfire the spark plug wires' order on the cap(s) may be out of their proper sequence. If you run the distributor test discussed on this page and find the engine idles significantly differently when run on the directly connected distributor on the right versus the belt-driven one on the left your vehicle may have some ignition wires attached to the distributor in the wrong order. This causes out-of-time detonation and is very hard on the engine and so should be investigated immediately before driving the car any further.  

Here is some more information about installing the high-voltage ignition / spark plug wires:
https://edelweiss.smugmug.com/Cars/Porsche-Technical-Stuff/Beru-Ignition-Cables/

 The mercurial fuel delivery system in a 993 engine, 

and how to make a quick diagnosis of it, or at least rule it out as a source of poor running:
If your 993 is a '96 or later, consider using an OBDII scanner to monitor the long & short-term fuel trims. This can provide insight into your fuel mixture, which should help you diagnose fuel delivery, for example,. fuel pressure, injectors, MAF sensor, as the root cause of poor running:. 

• The long-term trim should be very close to zero percent;
• The short-term trim should fluctuate in small increments around zero percent.
• The before CAT O2 sensors' output should be varying from about .35 volts to about .65 volts.

In addition to the above here are some other items to consider if you are experiencing reoccurring misfire OBD Codes.

To do this you will need an OBDC Reader that can display running data, something called "actual values" with Durametric software. There are only two or three reasonably priced readers that can do this. More information on readers can be found here.

If you are experiencing a Check Engine light (CEL) with a cylinder-specific OBD Code on your reader, one of the most common reasons for a CEL:

• Clear the OBD code and see if it returns, then;
• If it does;
• Clean the Idle valve;
• If the car had the ignition serviced recently check the wire routing sequence to the plugs;
• Check that both distributor caps are not loose or have an ignition wire that is not fully seated.
• Check both distributor's coils by unplugging each center wire individually and restarting the car to see if the engine runs at all on just one for each. This will also verify the distributor belt is in place.
• Check the inside of the distributor caps, if visible carbon trails around the inside of the caps or heavy carbon on the rotor tip replace or clean the caps and rotors.

If any of the above look suspect address the issue. Then in any case then clear the code and see if it returns.

• If the code returns:
• Consider replacing the one ignition wire.
• Then remove and inspect the one sparkplug. It should be lightly ashed. If wet with fuel investigate the fuel injector and have the injector cleaned or replaced.
• If wet with oil clean it off with carb cleaner reinstall it and verify the oil is not overfilled. Overfilling is quite common.
• Clear the code that has returned and see if it returns again

Somewhere along the above sequence, the check engine light will likely not return.

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 coin consider a donation through the button on the top left margin of this page.

#Varioram #Vacuum #PoorRunning #Actuators #MAF #AirFlowSensor #fuelPressure, # injector 

#misfire #backfire #idle

The Odometer a Known Issue

Replace Odometer gears - The advantage of doing this repair as a preventative fix is you won’t have to fish around and find all the tiny gear fragments. This seems to be an age-related issue, eventually, every 964 & 993 owner will encounter it. Two of the plastic internal parts, a gear, and the larger pod it attaches to become brittle with age. An easy kitchen table project to do.

The gear sets are available at multiple online aftermarket Porsche suppliers or even eBay. Be aware there are slightly different gears & pods with different numbers of gear teeth depending on the market where your car was originally delivered.

For example, if your car is the USA-delivered 993 the gear set is for a 993 sold originally in the USA market. The other way to ensure you get the correct parts is to count the number of teeth on the original gear & pod and buy the replacement parts with the same number of teeth. Also, see “How to repair a broken odometer”  on p-car.com or similar tutorials such as this available on several other 993 enthusiast sites. 

The most challenging part is to release the bezel ring to remove the glass to gain access to the internals. It is not really difficult but requires one to go slow and use some care bending the rear-facing bezel edge to get it loose. Even if the rear-facing part of the bezel exhibits creasing from removing it, it doesn't show upon reassembly and does not influence the bezel's function going forward.

Brakes & Rotors

Brakes are noisy!

The ugly fact of engineering is brake caliper systems are noisy, all of them, period! The challenge of the engineers of these systems is to minimize caliper/pad/rotor noise within the human hearing audio spectrum.  This might explain why your dog seems to launch into a sing-along

aria when you touch the brakes on your car for no apparent reason. Controlling brake noise is very hard to do as brakes being a dynamic slipping friction clutch application have a lot of variability in what is going on when you press on the brakes. Knowing this, at best one can only try to minimize brake noise and even then with highly variable success. This is why brake noise is the number one complaint mechanics receive related to brake work, "hey that's not a problem, that's a feature".  My experience is that if one uses the relatively soft OE dealer or aftermarket pads and replaces the spiders it will not eliminate but will likely minimize the occurrence of brake squeal. Also on a 993 as the rotors approach their minimum wear specification brakes can be a bit noisier.

Don't look for love too hard, try this first!

Recently a friend of mine was experiencing brake squeal with his 993 at low-speed stops. On his car brake pad and rotor wear seemed to not be the issue. He resolved the problem by making a series of aggressive stops at a relatively high speed of 40~60mph. His problem may have had to do with the pads not being fully bedded to the rotors, the added heat adding to the curing process of the brake pad friction material, or any number of other root or contributing factors. In any event, having heard this if your brakes are squealing at low-speed stops and the pads and rotors seem to be in good shape I would try heating up the system in this way before investigating the issue any further.

Brake warning light. The reason the light comes on is when a sensor clipped to one of the brake pads is ground down to the point that it becomes an open circuit.

Option to eliminate the brake wear sensors:

On my car, I soldered the sensors' wires together, insulated them, and tie-wrapped them out of the way against the struts. If one visually inspects their brake pads every 30K~40K, something that happens every year or two in many states due to mandated state safety inspections, there is no need for the expensive sensors.

Replacing Brake Pads

A Wear Sensor

Pads need to be replaced when the friction material looks to be thinner than the backing plate. It can be difficult to observe the friction material directly with the wheel on. I use 2 popsicle sticks held together as a feeler gauge to check the friction material thickness without taking the wheel off.  Pads worn to the minimum or rotors running near their maximum wear limits tend to contribute to greater instances of brake squeal on the 993. 

Replacing the brake pads can be done with the calipers in place or removed.  Replacing the pads is relatively easy however Porsche specifies that if you remove the front calipers you must use new bolts to remount them. I do not know definitively why this is needed but Porsche wouldn’t specify this unless they saw a failure in a test so I just do it. Taking the pads out without removing the calipers is easy however one needs to use a 1” metal paint spatula to slice the squeal silencers, sometimes called spiders or noise clips off the pads' backing plate so the pads can be removed.

Some replace the spiders when installing new pads some don’t. If you don't use spiders when mounting the brake pads you may experience greater brake noise. You will also hear an occasional clicking sound at times as the pads are not held firmly in place.

A brake pad Spider

The price of new silencer/spiders is high at the dealer and seeing that one will need 16 of them for our cars the total cost can add up to $200. A good inexpensive source for the common-sized ones is rockauto.com where they are priced between $3 and $6 each for the various sizes needed or about $80 for a complete set for all four wheel-ends.
For my 1996 narrow-body Carrera-2 here are the ones I ordered recently from RockAuto.com:

4 each of the below part numbers for all 4 wheel-ends:

96535109600 (351 096 00) - 44MM - Front

96435109601 (351 096 01) - 36MM - Front

96535209601 (352 096 01) - 34MM - Rear

99635208600 (352 086 00) - 36MM - Rear

Other models will need different combinations of sizes as listed in the parts catalog.

Reusing Spiders;

The spiders from Rock Auto seem to have thin sheet metal mounting discs vs the older ones, I seem to recall, came with rubber discs. For this reason, I see no reason why the newer metal spiders can not be reused. This is done by cleanly slicing them off the backing plate initially as part of removing the old pads with a 1" metal spatula. Then if needed the bending of the metal tines at their center out just a little so they snap in cleanly when reused.

When reapplying them hose them off with a little spray brake cleaner and use some 3M™ Adhesive Transfer Tape 468MP on the spiders' disk face as an adhesive to reapply the spiders. This tape is rated for use up to 400 Degrees F. 

An alternative is to use the readily available brake anti-squeal compound/adhesive for example CRC

05016 Disc Brake Quiet. If one uses this liquid compound type adhesive apply it to the spider's mounting disk face sparingly smoothing it as a very thin layer over the spider's disk and not to the very edge of the disk, and let it dry a bit before clipping the spider into the caliper cup. Doing this will avoid it oozing out from under the disk and gluing the backing plate to the caliper piston cup seals. By using care in the application of the adhesive compound the seal is not damaged the next time the brake pads are removed.

Selecting pads for a quiet ride:

Pads from the dealership are staggeringly expensive so if shopping for aftermarket pads that will run quietly look for very soft organic pads if you can find them or alternatively street pads that list low noise as an operating feature such as Centric's Posi Quiet pads or similar from other suppliers. In most cases, they are either organic or semi-metallic pads intended for street use and should be reasonably quiet. The operative word being "should". Pads that are marketed as performance pads or pads for track use are usually made of a harder compound, designed to run at higher temperatures, and generally are more prone to squealing noise. I have used pads from the dealer, Textar, and Centric/Stop Tech. It seems that how quiet a pad runs is a little hit or miss.

Little things to make changing the pads a lot easier:

• If the brake reservoir is nearly full or full I draw it down a little with a turkey baster or a syringe before working on the brakes. After installing the pads on each wheel end I pump the brake peddle a little pushing the caliper pistons against the new pads and rotor. In this way it avoids the cumulative effect of all the wheel ends having all their piston cups fully pushed in causing a good volume of brake fluid to back up into the reservoir potentially overflowing it and making a mess.
• I compress the caliper piston cups using a "C" clamp while the old pads are still in place. Placing it along the top edge of the caliper casting and the pad backing plate. If you have a concern about scratching the paint on the caliper face one can use a little patch of rubber to protect it from the "C" clamps jaw.
• A small but key item when removing the caliper hold-in bowtie spring is to detach the little metal

  

  Detaching the Sensor clip

  
  clip that holds the wear sensor wire from the center of the bowtie spring before squeezing the bowtie to release it. The clip seems to interfere with compressing the bowtie just enough to make it difficult to pop the bowtie free from the caliper housing.
• The two spiders' discs must be sliced free from the backside of each pad to release the pad. I found using a one-inch metal painter's spatula and sliding it behind the pad from the center of the pad at an angle toward each spider seems to release them readily.
• When installing new pads with spiders without removing the caliper I find pealing off the spider's adhesive backing plate covers first and snapping the spiders into the piston cups before guiding the new pads into position seems to be the way to go.

  

  Squeezing the Bowtie

  
  Using the spatula seems to facilitate this. Once the brakes are cycled for the first time the adhesive will be pressed firmly against the backing plates. 
• If one of the spiders seems to not snap in smartly and wants to fall out just bent out the little tines on its metal center clip a little and it will hold fast when snapped in. 
• It may be necessary to slightly champer the inner curved edge of the pad friction blocks to provide clearance to get the pads to slip into the caliper easily.
• I also chamfer the leading and tail edges of the pad's friction blocks very slightly as it seems to minimize squealing early on with a new set of pads.

Cleaning up the look of the wheel nuts and calipers at your next brake pad change: 

While you have the wheels off consider applying a quick shot of gloss black paint

to the worn anodizing on the nuts. Only the top of the nuts' caps really needs to be painted completely as it is really the only part one can readily see when the nuts are installed. As I worked my way around the car replacing the brake pads I give a shot of paint to the nuts for that wheel. By the time I am ready to remount the wheel the paint is dry enough to handle the wheel nuts with a little care. 

Cleaning up the look of the calipers:

Also if your calipers look dull and the clear coat has chipped off one can

restore them as they work their way around the car using the method on this page.

Evaluating rotors for replacement:

The official way is to measure the thickness of the rotor to make sure it is greater than the OE minimum specification of 30mm in the front and 22mm in the rear. The shade tree approach is if there is a good size ridge on the outer edge of the rotor where the pad does not touch the rotor face they should be considered for replacement.

Ridge formed at the rotor's edge.

Keep in mind there is only a 2mm overall difference in rotor thickness between a new rotor and one that has reached its wear limit. This translates into an approximate 1mm ridge having formed around the circumference of each face of the rotor.

OE supplier to Porsche drilled rotors can be purchased online at Rock Auto at a surprisingly affordable price. If you took the calipers off to replace the pads one need only remove two rotor hold-down screws to replace the rotors. The screws are best removed with a manual impact screwdriver, an inexpensive tool purchased at Harbor Freight.

Impact Driver

I always paint the contact surfaces of the rotor to the hub and the hold-down screw with anti-seize when mounting rotors as it will make the rotors easier to remove in the future. The same goes for the rotor contact points on the wheel hub.

Here is a detailed procedure for replacing rotors.

Styles of Aftermarket Rotors:

A question that is regularly asked is are the drilled (original design), slotted or plain-faced rotors best. Although the engineers designed the braking system thinking about rotor weight, pad heat gassing, and air path for cooling, I feel, the brakes on a 993 have significant excess capacity beyond that needed for street use and speeds so the style of the rotor probably doesn't matter much for street use. Now for cars that are raced, I would go with the factory configuration as it has been extensively tested for performance and reliability. Also, the configuration of the fins internal to the rotor is very specific to optimize cooling so for high-performance driving I would stick to rotors from the suppliers who originally supplied rotors to the factory at assembly or rotors supplied specifically for racing applications on the 993.

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.

Noisy Fuel Pump

Replacement fuel pump – 

 Is that noisy fuel pump a failing pump or simply $3 worth of dried-out pump isolation mounting grommets? 

On cars with 90K miles or more on them with an original fuel pump and someone is experiencing what seems to be intermittent fuel supply issues, replacing the DME relay should be the first action. If that doesn't solve the issue, the fuel filter should be replaced, and then consider replacing the pump. A new pump is about $125 in a BOSCH box.

Also if the pump seems to be the root cause of hard starting the fuel pressure can be checked at the Schrader valve on the driver side fuel rail where the static pressure should be at 3.8 bar or at idle a bit higher.

Idle, Ignition & Misfire issues

Rough or high idle after disconnecting the battery. The BOSCH Motronic ECU over time adapts to a specific engine resulting in a consistent and relatively smooth 800 rpm idle +/- 40 rpm. When the car's battery is detached this adapted information is lost and over a short subsequent running period, the information is recreated by the ECU. I have been told, but have not verified that if the car exhibits a high idle RPM, say 1200 RPM,  and suspect sources of this condition such as the idle valve and the Mass Air Flow Sensor have been addressed the car can be left at idle for ten minutes and the ECU will adapt and the idle will return to normal.

Replace ignition wires – Ignition wires have proven to be long-wearing, some have needed to replace them in as little as 60K miles others much longer. In my case, I replaced them at 80K miles even though they were not exhibiting any issues or misfire codes as it was an economical add-on item to other work at the time.

If your car is not throwing misfire codes, you are not experiencing ignition problems in wet weather and the wire ends look good you can probably hold off on replacing them as a preventative maintenance item. However, if your car has over 60K miles on it and you will have the engine out or the valve covers off for other reasons the incremental labor to replace them should be low and so replacing them may be considered.

Replace plugs - Plugs are generally extremely long service life items on a 993. I would not replace them unless your car has miles in excess of 80K and you are having the engine out or its ancillaries removed for other reasons as replacing the plugs alone is labor-intensive.

If you do not have a diagnostic misfire code attributable to worn plugs avoid the temptation to mess with them. If you do have such issues check the cap & rotor first then the ignition wire involved as these are more common reasons for such codes. A non-cylinder specific or multiple concurrent cylinder specific misfire codes are usually not caused by a wire, plug or injector and are more likely related to systemic issues like a vacuum leak, a dirty idle valve or an oxygen sensor out of specification. By the way, it is OK to replace just one ignition wire or plug as needed.

Replace rotor & cap – IF there is a concern about rough idling. 993 does not exhibit a perfectly smooth idle so what is normal is learned with experience.

My experience is that if one starts from cold a 993 without giving the engine a little throttle blip once started it may settle down in a very slow uneven idle. In this situation, it may even illuminate the check engine light and throw a random misfire code. The solution to this is to clear the code and move on.

I found that caps and rotors seem to be a two to three-year repeat item on my car. If I leave them longer at some point I get a check engine light and a reoccurring random misfire diagnostic code that keeps coming back when cleared. So about every two years, I have been replacing the caps and rotors on my engine.

Having lived in Northern Ohio (wet) and now Virginia (humid) it seems the small amount of motor oil applied to the pad in the center of the rotor shaft at rotor replacement and oil changes may have contributed to the total lack of corrosion on the internal parts of the distributor assembly on my car. This, in turn, may be why I have never experienced the common corrosion-related distributor bearing failure leading to a broken internal distributor belt.

Recently I tried 1500 grit sandpaper to polish the carbon tracks off the rotor and I hosed out the inside of the distributor caps with spray electronic cleaner. This seems to have done the trick extending the life of the parts somewhat. I for some reason kept some of the old caps and rotors, and now I have a lifetime supply of two-year-old rotors and caps that can be put back into service if needed. On one occasion I got a check engine light and upon inspection found one of the distributor caps was a little loose. I tightened it up and the light went out shortly thereafter. Even though the caps are plastic and I do not want to distort or crack a cap I will need to make sure the distributor cap screws are a bit tighter in the future, a bit beyond lightly hand snug.

Also, here is a page discussing insidious power robbing items that can be investigated.

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 coin consider a donation through the button on the top left margin of this page.

Hydraulic Lifter Noises

Replacement of hydraulic lifter cartridges - IF noisy, sounds like a bucket of ball bearings rattling around, at startup after sitting for a day or two; if car sits for an extended period such as a month and the sound presents on the first startup but disappears thereafter and does not return on a subsequent restart this is a sign that the lifter cartridge seals may leak a bit but have not progressed to the point where cartridge replacement is indicated.

This seems to be a chronological age-related issue as the cartridge seals lose elasticity and slip off causing the cartridges to no longer retain their oil or proper function at initial start-up. This issue presented for me about the same time as the need for clutch replacement at 80k miles on my car.  Replacing them involved removing the valve covers and presents the opportunity to replace the valve cover seals, plugs and wires at the same time incurring minimal additional labor to do so.

The 993/964, G50/G64 Variant Transmissions, servicing and repair.

 

Back around 1998, I was at a meeting at a Dana Spicer training center, and in the lobby was a display case with a G50 Variant transmission in it. Turns out that at the time every part in these transmissions was made in Michigan and then shipped off to Getrag Germany for assembly, go figure?

Over time the manual transmissions in the 993 & 964  have proven to be extremely durable and with regular gear oil changes can provide trouble-free service well over 100,000 miles. 

Do you have a limited-slip differential internal to the transmission case? A quick test is to put the back wheels in the air with the transmission in gear. If you turn one of the rear wheels and the other rotates in the opposite direction your car is equipped with a standard differential. If the other wheel rotates in the same direction your car is equipped with a limited slip differential.

The other way is to look at the option code sticker under the frunk lid or in the owner's manual.  

*Here are the related option codes:

1. 219 Regular differential (without limited slip) 
2. 220 LSD Limited Slip Differential with 40% lock 
3. 224 ABD Automatic Braking Differential (Traction control), An Automatic Brake Differential (ABD) system works by using the Anti-lock Braking System (ABS) to apply braking power to any individual wheel that may be slipping during acceleration.

*In cases where this feature is standard on a vehicle, it may not be listed on the option code sticker.

All G50 Varient transmissions are a constant mesh design, meaning all the gear pair sets are fully engaged to their mating gear and spin freely until by shifting into a specific gear their attendant synchronizer ring locks the specific gear set in as an active part of the driveline. In this design, the actual gear sets are not subject to wear from engaging or disengaging only the synchro rings that facilitate their locking in wear over time. 

Because the lower gears are subject to a greater number of gear changes while driving and because of the greater speed differential the lower gear synchros need to deal with they are the first ones to usually exhibit wear out in a street-driven car. In fact, when disassembling the gearbox for service the first and second-gear synchros can exhibit extensive wear whereas the synchros for the upper gears show little or no apparent wear. This is why unacceptable shifting experience tends to show up shifting between the lower gears first.

On rare occasions, a street-driven car with as little as 80K miles on the odometer may need servicing if it exhibits shifting problems that can not be attributed to problems with: 

• The need to have the clutch actuation hydraulics bled to remove air,
• The hydraulic clutch actuation or the lever in the peddle cluster, 
• A worn clutch, 
• Out-of-adjustment or worn shift linkage components or
• Failed engine mounts; 

Engine mounts are easily tested by slightly lifting the engine from the engine case using a hydraulic floor jack placed on the reinforced center of the engine case a bit forward of the  oil drain plug outlet. If one sees more that just a smidgen of vertical movement of the exaust pipe tips the engine mounts probably need to be replaced. Never use the engine case to lift the rear of the vehicle off the ground as it is specifically verboten in the owners manual and discussed here.

Also if you are new to the 993/964 it is important to push the clutch pedal all the way to the floor and that any carpeting added doesn't interfere with this. If not pushed all the way in some cases one will experience grinding while shifting. I have found sliding the driver seat a notch or two forward eliminates the tendency to not push the clutch pedal all the way to the floor.

Metal grit at the drain plug -- Shiney, usually gold-colored, metal grit found at the gear oil drain plug is normal in these transmissions as the synchro friction rings are sacrificed and with use over time. The synchro teeth even if heavily worn will generally outlast the friction face on the synchronizer's rings by a long shot so the grit found at the drain plug really is not a sign of the need for transmission servicing in the absence of other gross operating symptoms. 

1st & 2nd gear synchros & grinding – Grinding is the sound and feel of the system slipping over multiple synchro teeth with every shift into a specific gear. This is not a common occurrence, just an experience I had. If the gears exhibit a single ding or two when cold that is mitigated by slightly slower shifting and it disappears completely once the tranny warms up, this seems to be normal for many of these cars as the transmission ages and the synchro friction rings lose some of their effectiveness. It does not necessarily require servicing. However, if the gears grind with every shift into a specific gear and the problem only gets worse with a gear lubricant refresh it is a dead giveaway you have this issue that should be investigated. This was an 80K+ odometer item for me.

I have read endless circular discussions concerning shifting feel and various brands and viscosities of gear lubricants. My view is, as the synchronizer friction rings become worn their ability to grip and synchronize the gears is diminished very gradually over many miles of use.

At some point, the ability of the rings to grip is so tenuous that very small changes in lube viscosity or temperature can result in significant differences in shifting acceptability. At this point, I feel looking for a gear lubricant one likes better may not be the answer. The transmission may simply need to be serviced and have any synchro rings exhibiting wear replaced. Usually, this is only the 1st & 2nd gear rings. On the upside, unlike earlier 911s the 993 does not require the engine to be removed to service the transmission or clutch.

 More information concerning gear lubricants can be found near the bottom of this page under the section labeled "Manual Transmission Gear Lubricants."

Metal chunks at the drain plug & repairing the differential  – When the transmission is open for synchro replacement on a base model Carrera the ring gear on the stock differential may exhibit some steel chips missing from its face along with these metal chips showing up at the drain plug.

Any shop that does a reasonable amount of Porsche transmission work will have a used or repaired standard differential on hand. This is because many times when a previous customer upgraded to a limited-slip differential the shop retained the original. These parts may be available at a very low cost to you. 

I have an unsubstantiated theory that when a base Carrera, which doesn't have a limited-slip differential, is pushed to the point of wheel spin, at the point where the tire reestablishes grip it jackhammers the standard differential gears. This may be the cause of rather large steel gouged chips from the ring gear face showing up at the transmission lubricant drain plug. 

Although seeing these chips can be disturbing they are not an indication of a serious issue with the transmission requiring immediate repair as many folks seem to drive their cars subsequently for thousands of trouble-free miles and only become aware of the damage at a gear lubricant refresh.

Engine vibration and body boom after replacing the transmission mount:
The original transmission mount for the standard G50.20/21 transmissions was 

Transmission
Mount

964 375 055 02. It has now been superseded and consolidated with 964 375 055 81 originally specified for G50.31/31/33 series used in a Carrera RS. The new part has both 964 375 055 81 and 964 375 055 82 printed on it. The rubber in the new part appears to be much stiffer than the original which transfers greater vibration into the car which has caused dissatisfaction for car owners. There are examples of owners spending large amounts of time and money looking for the root cause of the vibration in the clutch or internal to the transmission. 

Others feel the new mounts can be reasonably quiet if installed correctly. Claiming "if one deviates in the rotation of the mount [from the correct position] at installation by more than 10 degrees or so you will have horrendous NVH (noise, vibration, harshness) problems." They reference a picture in the shop manual for guidance on properly installing the mount.

Until Porsche sorts out this issue or an aftermarket manufacturer

Assembly Mark "A"
must point upwards for
 the correct positioning
of the mount.

sorts it out for them it may be a good idea to hold off on refreshing the transmission mount as part of servicing a clutch or transmission on a 964 or 993.

Here is a page that discusses the clutch and its role in shifting issues.

Here is a page that discusses engine mounts and their influence on shifting.

Here is a page that discusses related flywheel issues.

Another anecdotal solution to a transmission noise problem:

Recently I came across a posting on social media where the author has his car set up with an RS Light Weight Single Mass Flywheel, The RS transmission, and the stiffer RS motor mounts. His experience is that changing brands of transmission gear oil contributed significantly to quieting down transmission noise even with his setup which is inherently noisy.

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 aggravation, time or even some coin consider a donation through the button on the top left margin of this page.

1996 Engine Wiring Diagrams

Warning these drawings were pasted together from paper page images and do not line up exactly and so may misrepresent circuits near the joined pages where the page sections meet. Also, there are a few variants of the engine's harness by market for the model year 1996 so not all harness versions exactly match these drawings. For these reasons use these drawings at your own risk.

To download any or all of the below pages follow the below link and click on the desired page:
https://www.dropbox.com/sh/kdcer08sakqlun6/AABG8n24M_zVOAw5kJKl9wtla?dl=0

General 993 Wiring Diagrams

Most of the 1995 wiring diagram detail is carried forward to later years. Significant differences have to do with the Motronic ECU wiring to the engine in OBD-II and Varioram-equipped engines.  

To download any or all of the 993 Wiring Diagram pages in high resolution, 

"follow this link and click on the desired page".

If you are looking for the OBD-II engine and varioram wiring it can be found here:

https://993servicerepair.blogspot.com/2020/04/1996-engine-wiring-diagrams.html

Fuse Box Cover Fuses and Relay Legend 1996 OBD-II Varioram USA 993

Click here for a high-resolution image of the Fuse Box Cover Legend  

for a 1996 OBD-II Varioram USA delivered 993

Fuse Box Relay descriptions:

#Fuse #Fuse Cover #fuse list #fuse box #fuse legend

Fuse Box

Relay Diagram

Realy legend

Fuse descriptions

Clutch, Master & Slave Cylinder and Peddle Cluster Kinematic Lever Issues

     

Clutch - IF not replaced once in the past. All sorts of shifting issues can present when a clutch is at the end of its life including slipping on acceleration, a hard to actuate clutch even dinging gears when shifting. A 993 should shift as easily as a Honda Civic. If this is not your experience have it looked at.

Clutch Hydraulic Actuation and Peddle -  If you are experiencing changes in the behavior or smoothness of travel of your clutch peddle you may have a leaking clutch cylinder or a failed clutch peddle lever. In my experience, this can quickly digress into being unable to actuate the clutch at all. The master and slave clutch cylinders should both be replaced at the same time, if original, once one begins to leak. Also, consider replacing the kinematic clutch lever in the peddle cluster at the same time as it is a known failure point on the 993 even after multiple design revisions.

According to the 993 factory shop manual - the solution to fix the clutch pedal not fully returning problem is to replace the kinematic lever in the clutch assembly.  The newest part number for the kinematic lever is 993.423.519.03, apparently, Porsche had a total of 4 different updates for this lever.  Defective part numbers are 993.423.519.00 or 993.423.519.01 (gold color).  The improved parts are 993.423.519.02 or 03 (olive color) 

I had a master cylinder failure shortly followed by a slave failure where the clutch lever was also broken, all at about 100K miles on my car.

Here is a page that discusses the G50 five & six-speed variant transmission and its role in shifting issues.

Here is a page that discusses the clutch and its role in shifting issues.

Here is a page that discussed related flywheel issues.

Here is a page that discusses servicing the shift linkage.

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