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Frequently Asked Questions (FAQ), Procedures and Resources


Old 12-25-2006, 09:38 AM
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Default Frequently Asked Questions (FAQ), Procedures and Resources

This is modelled loosely on the Audi 100/A6 (C4 92-97) FAQ Digest page (see URL)

This is how it works: Basically we put a short articles or links to good posts as replies to this thread. You can upload pictures to the and attach them to your articles. Please follow the structure of the thread.

Also if you are about to type a comprehensive answer, type it in the FAQ thread list below this post or make a link to it in the FAQ thread. Always check to see if a thread has already been started in the FAQ, e.g. Cam Position Sensor (CPS), etc.

- Please refrain from asking questions, flaming people or posting a thank you in this collection. Post those on the main forum!

- Try to keep links linking to other sites to a minimum since they may not be there in the future. The same goes for using pictures from someone elses picture poster; those will be gone at some time as well.

To find things, either browse down the list or if you want something more directed, use your brower's "FIND IN PAGE" feature.

Thanks from the staff at STFA (Search the Forum Archives)(or, on a bad day, Search the Freakin' Archives!!!)<ul><li><a href="">Link to C4 A6/100 forum FAQ - which has lots of common C4 BTDTs</a></li></ul>
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Old 12-25-2006, 10:27 AM
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Default Fuel Pump Replacement

Our 43 mm diameter fuel pumps have a finite life. They can fail as early as 80,000 miles or last as long as 250,000 miles. However, since they give little or no warning before they die (a bit longer cranking one or two days before they die), I personally advocate changing them every 100,000 miles (or less). They aren't that expensive ($120) if you do the work yourself. The procedure below works.

Best if you drive the car until the 15 L remaining fuel warning light comes on. That way you don't have to syphon fuel or have your arm in fuel to your elbow. To reduce the fuel pressure in the system, remove the gas cap, start the car and then remove the 20 amp No. 17 fuel pump fuse (panel at the drivers (LHD) end of the dash) and run the engine until it stops. Then remove the rear seat and disconnect the battery (have the radio code handy).

Ventilation!! Take a break if you feel dizzy. Better yet wear a vapour mask with carbon canisters.

See the URL for the procedure.<ul><li><a href=""></a</li></ul>

Last edited by UrS4boy; 05-09-2009 at 06:08 PM.
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Old 12-25-2006, 10:33 AM
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Default Missing and/or hesitation diagnostic procedures

The AAN will develop misses when there is spark plug, spark plug boot, coil, power output stagen (POS) or even MAF to Turbo hose problems. It can be nightmare to find the problem. Fortunately, there have been enough BTDTs that there are some logical procedures to help you figure out what the problem is an how to fix it.

See the posts below.
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Old 12-25-2006, 10:37 AM
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Default One missing and hesitation diagnostic procedure (for POS and Coils)

This one should help you to sort things out. If the miss is just under boost, it is most often a coil but could be plugs or boots or even the MAF to Turbo hose. If the miss is all the time, it is likely one of the POS channels dieing.

Follow the procedure below and you should be able to sort it out.<ul><li><a href=""></a</li></ul>
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Old 12-25-2006, 10:43 AM
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Default Fuel pump relay installation.

The fuel pump is powered by the general 12V power system. In stock form, the power goes from the battery (under the rear seat) to the ignition switch and then all the way back to the fuel pump (located in the trunk area, behind the battery). Since the wire gauge Audi used isn't the best, there are line losses of about 1 V. This may not seem like much but under load, e.g. Wide open throttle (WOT) and big boost, this lost 1 V is very important to the pump's ability to provide enough fuel. The solution is to relay the fuel pump to the battery (about 4 ft from the fuel pump). Sean D. and I developed a procedure to install such a relay. The result is the write-up in the URL below.<ul><li><a href=""></a</li></ul>
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Old 12-25-2006, 06:04 PM
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Abbreviations Defined
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Old 12-25-2006, 06:07 PM
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Default STFA

1.) Search The Forum Archives
2.) Search The ****in' Archives

<b>Alternative Definitions:</b>
1.) Stay The **** Away
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Old 12-25-2006, 06:29 PM
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Default Life at 200k+ miles (long)

Life at 200k
By Paul Rivera - Quattro Quarterly, Fall 2001

For the Urq/S4 owners reading this, it will all be familiar. For those of you coveting ownership of this marvelous car, here is a little insight of what it's like to own one for an extended period.

Older Mercedes models, like the W123 chassis have a great reputation for durability and being able to run up to 1 million kilometers. Just ask the taxi drivers in Germany. In my opinion, modern Audis (1986 and newer) have that same capability. Our family Audi fleet is an example of this.

Having two S4s in our family, the '93 at 200K miles, and the '94 approaching 120K miles, has given us quite a knowledge base of just what one can expect "real-world" in owning these incredible cars.

Mike Rooney, of Ingolstadt West Audi Service in Chatsworth, California, is my resident S4 "Meister-wrench". I tapped him to assist in providing additional information for this story. He helps to maintain our fleet of 5 Audis in the family. Manfred Hageldorn, formerly of Rusnak Pasadena, moved back to Augsburg, Germany, and the other great Rusnak wrench was Johnny Reyes, recently hired by Audi Powertrain Development. Mike has taken their crown as the best Audi mechanic in this area. Manfred by the way, is now wrenching BMWs and has recently told me how superior he feels Audi engineering and production quality is to BMW (he is a little biased).

C4/S4s, built from 1992 to 1994, and C4/S6s, from 1995 to 1997, are identical in chassis design to the 100/A6 model sold between 1992 and 1997. C4 is the chassis identifier for a full size Audi chassis built in this era. Audi V8s and A8s are "D", and Audi 80/90 as well as A4 models are "B" chassis. We are now on the C5 chassis series (A6 1998 to?). Changes in tuning for the Urq/S4 (original) included not only power train, but springs, shocks, front sway bars, and rear sway bars fitted in some years. Also, there was a running production change with an additional firewall bracing upgrade installed starting in late 1992 and early 1993 C4 models. Interior details, like white face gauges, premium leather seating, and Bose Stereo systems were all standard in the USA specifications for this top of the line model. For the lucky few, S6 station wagons were imported between 1995 and 1997. Unfortunately, Audi USA never imported the V8 version of this car sold in Europe between 1992 and 1997. The V8 powered S6 Plus, sporting the S8 motor and 326 HP was the best and last of this model. Not to fret, as you read this, the new C5 based S6 Avant, with the S8-V8 and 340 HP, will be on the way to your local Audi dealer. Get one while you can!

The single most important section of this fine car is it's incredible power-train-five cylinders, 20 valves, dual overhead camshafts, fuel injection, and most of all, a sweet turbocharger. This motor, referred to as AAN, began life in the USA as a 3B motor in the 1991 Audi 200 20V turbo quattro. Audi engine boffins changed just about everything on the intake, injection and ignition side, as well as a totally different transmission, making this power-train the greatest and last example of the Audi 5 cylinder engine. As a side note, Acura-Honda, Volvo, and Fiat started making 5 Cyl. DOHC motors soon before Audi stopped. A real testimony to the vision of Dr. Pi?ch, the man behind the Audi 5 Cyl. concept.

You could call me a maintenance freak. I abhor any dirty or old lubricant, old anti-freeze, and especially old brake fluid. Timing belt changes become a religious discipline. Service schedules from the factory in my opinion are tuned to lower costs in the first tier of ownership, without regard to extending the life of the vehicle's power-train and brake system. How many times have you read "lifetime filled". Lifetime of who or what, the component in question? With my mentality of maintenance, I have received the reward for extremely long life of all of my cars. What I have found is that most S4 owners tend to be the same towards their cars.

There have been so many studies from MBA types that find the most optimum time to sell your car is below 50K miles. As the S4s in my family have been very reliable, I see no reason to sell the car at all. In fact we are expecting to keep the cars for some time to come.

Mike Rooney and I had a long lunch recently and reviewed not only the work that was done on our cars, but also things he has seen with all the other S4s he services.

When we listed all the areas of potential maintenance, it seemed like quite a scary list. Not all of these things have happened to either of our cars. However, if you look to buy a used one with high miles, or you too are set on a "keeper", you can expect some or all of these areas to need attention at some point in the car's life.

Mike says "Keeping clean lubricants and fluids is the cheapest form of preventative maintenance. I advise using high quality synthetics, like Castrol Syntech, Mobil 1, and Red Line. Change your synthetic engine oil at 5K intervals to be safe. Always use a German brand such as Mann, Mahle, Knecht, or authentic Audi Oil filter. Do not use Generic Orange, Yellow, White, or Blue filters (no names listed for law suit sake). The correct filters have 2 internal valves, a drain back valve and a by-pass valve. Most generic K-Mart/Pep Boys brands do not. If you use ordinary motor oils, please take care as I have seen even the famous Yellow brand form a gelatinous goop that can coat valve train components and end up clogging the pickup screen of the oil pump and cause oil starvation. I advise use of Castrol GTX, or Kendall Racing, with 3K oil change intervals. If you use a "Quick-Lube" place for oil changes, bring them the filter. Change the transmission and rear differential lubricant at 60K intervals at a minimum, preferably @ 30K using Audi/VW or Red Line synthetic gear lube. Brake fluid should only be Dot 4. Castrol, Mercedes, Audi/VW, or ATE. I do not advise use of domestic brands. Change at least annually and be sure to flush and bleed the clutch master and slave cylinders at the same time. Hydraulic Fluid for the steering/brake pump should be flushed and changed at the 30K service (at least), with the filter screen replaced if necessary. Use Pentosin or Audi/VW Synthetic only. Coolants should be phosphorous free, like the Audi/VW brand, Mercedes, or some other high quality brand. Change this annually as well. Most important major service is the 60K, when the timing belt, water pump, tensioner, and serpentine belt should be replaced in one shot. Saves a lot of labor cost as the water pump often does not last to the 120K service. Make sure you get your car on a hoist once in awhile so you can inspect the areas near the rear differential, drive shaft, and CV boots. Hard to see some problems when you are underneath the car.

It is rare that I have seen any S4 with enough miles to warrant rebuilding the bottom end. Valve trains seem to last well over 250K, with good fuel, clean lubricants and coolant, and a tuned motor extending the heads life. S4 motors well maintained could last up to 350K miles.

Below the approximate miles are listed in which you can expect parts to fail or need changing, and areas that need closer scrutiny.

Timing Belt and Serpentine Belt 60K.

Timing Belt Rollers and Tensioner, 60-120K

Power Steering/Brake Pump. Usually the seals will fail at 60-100K, and if you get an authentic ZF Seal kit, you can save the cost of buying a new pump.

Brake Accumulator. This is an expensive part and will last anywhere up 200K miles, yet may fail as early as 50K. A valve inside of the unit fails and renders the unit useless.

Steering rack. Usually it is seals as well that fail in this part. They can be re-sealed cheaper than replacing the unit. This will occur somewhere between 80-150K miles. Mike has resealed both of our cars once. High pressure accumulator and steering rack hoses are long life and start needing replacement around 120-150K. Several of these have been changed in either car.

Cooling System. Hoses. At 90-120K miles, consider changing all of them at one shot. Saves grief later. Aftermarket sources of German OEM quality are less than $175 for a complete hose kit. The little hose for the turbo coolant is hidden and should be replaced as well. Radiator. Neither of our cars have needed replacement yet. Unlike our V8 and 1991 200 where they failed at about 100K miles (plastic end tanks crack).

Plastic Heater Valve fails @100-200K miles.

Coolant Bottle and Cap will need replacing @ 50-120K miles.

Water Pump 60-120 K Miles. Clean coolant helps extend life.

Cooling Fan Motor. Have not changed yet in either car.

Aux cooling pumps. They seem to develop leaks more than just fail. Usually before 100k. Both have been changed on both cars.

Heater core. Not changed yet, again clean coolant extends life, 120-200K miles is typical for life.

Fuel Injection.

Hoses. The braided portion of these hoses can leak. Audi did have a recall, and I have had both of our S4 hoses changed, at 50-100K Miles.

Injectors. Still have the originals in both cars. Use of Techcron at each oil change service, good fuel, and frequent change of fuel filter @30K intervals) is needed for long injector

Fuel Pump. When it starts making lots of noise, time for a change. Usually 100-150k miles. '93 was changed at 170K, '94 has yet to go.

Turbo Charger. Clean oil, and letting the engine idle and the turbo cool down after a hard run helps as well. Intercooler hoses will fail at 50-200K depending whether the rubber rots or the excessive boost on a chipped car blows it out. MTM makes some reinforced hoses that are worth upgrading to, or change them all to Silicone "Samco" hoses.

Brake system Calipers Front. Stock Girling G60's are bulletproof with clean fluid. We changed both of our cars to the Mov'it Brembo/Porsche 993 TT calipers and matching rotors.

Brake Pads Front 10-25K Miles

Brake rotors front should be changed at 2-3 pad change intervals. Check minimum thickness specs and measure.

Brake pads rear Up to 100K on these.

Brake rotors rear. Maybe change @ 100K-150K if needed. Maybe resurface is ok too for one pad change. Again, check for the thickness specs and measure/replace accordingly.

Brake caliper rear. Here is an area of concern for our east coast and wet weather area owners. The hand brake cable can get rusted quite easily and lock up. Keep the entire handbrake mechanism and cable assembly clean and lubricated, and make sure the cable boots are intact and packed with some light grease. Neither of our S4s have been afflicted with this yet. My 1986 5KCSTQ had it bad as it was an east coast car.

CV joints. These usually last up to 300K Miles if the boots are intact, full of grease, and never exposed to dirt. Ours are original on both cars.

CV boots. These can need replacing somewhere around 80K-120K miles. When you change your shocks or suspension, change the boots at the same time. Inspect them regularly at each oil change.

Suspension. Front lower control arm bushings are the first to go, with sub-frame bushing needing replacement if the car has been driven hard or on really bad roads.

Steering damper goes out about the same time. 100-150K miles. Tie rods and ball joints can last up to 250K miles.

Front Strut Bearings take a beating and need replacing when you change your front shocks if not sooner.

Rear suspension is pretty reliable with the exception of rear camber links at 120-150k miles. Shocks. 80-120K miles on the front. Rears last longer, but change all four at once. Mike Rooney likes Bilstein. Konis are great too. Personal subjective preference. Both S4s have Bilstein, with different valving on each of the cars.

Springs start to show sag at around 200K miles.

Wheel Bearings. Not changed yet. Mikes says they can and change them when they are noisy.

Interior. Only the leather seat side bolster driver's side shows wear on either S4. All other interior pieces are in great shape. If you use floor mats, chances are your carpets are fine. Audi interior quality just cannot be beat and it only gets better in the newer cars.

Ignition. Spark Plug connectors. Here is a 60K item. Best to change them @60K service along with the plugs. Especially if the car is chipped. Seems to be a dealer only item, but Blaufernugen has them as well.

Spark Plugs. Use ONLY Bosch F5DPOR Platinum. Change at 30K intervals. Do not even think about a different plug.

Crankshaft Hall Sensor. If the car has hot start problems, this is usually the culprit, but has not failed yet on either car. Mike sees this rarely.

Oxygen Sensor. Change at 30K intervals if in doubt as by 60K they are usually not working well. Aftermarket Bosch with Audi connectors are a lot cheaper than the dealer. You can use the universal 3 wire, but the $ savings is only about $30-$40 and to me not worth the work in splicing in the wires.

Exhaust System. Audi spent the money on a high quality system, and we have not had to change it yet. Folks in the snow belt and wet areas may have different experiences. If you do change, use a stainless steel replacement like Audi original, or a quality stainless like a Stebro.

Catalytic Converters. They seem to have a long life. Have not needed changing on either car. Keeping the motor in tune has helped, I am sure.

Electrical systems. Audi really worked out the bugs and S4s are not plagued by any systemic flaws. Alternators are high output and rarely fail. Starter motors can last to 250K miles. Neither car has had either changed yet.

Instrument lighting is a small gripe. The exterior temperature gauge backlight fails eventually, and either means replacing the unit ($150) or re-soldering a replacement bulb. When you pull the instrument cluster to change a bulb, change all of the bulbs at one shot.

Seat heaters. Usually the driver's side will fail sometime up to 150K miles.

Sunroof switches @100-200K miles. Window motors and Seat motors rarelyfail.

Clutch. This depends on driving style. '93 changed at 150K, '94 changed by first owner under warranty at 32K miles. He was a gorilla.

Master and slave cylinder life is dependent on clean and fresh brake fluid. When changing the clutch, change all related parts such as pressure plate, pilot bearing, thrust bearing, and if necessary, the dual mass flywheel. Also, change the rear main seal, using only an original Audi factory part. Aftermarket seals seem not to be as good says Mike.

Air Conditioning. Sensors need replacing from time to time, and also the temperature control flap motor gives out at about 100K.

Interior fan motor usually needs replacing by 150-200K. Same on my V8, and my 1991 200. Related hoses may leak more with age then mileage.

Compressors seem to have a long life and rarely need replacing. No real trouble areas.

Vacuum hoses can be a problem. Especially the ones that run along the firewall that are covered by a plastic trim piece. The rubber rots and the clamps do a poor job. Change the hoses and the clamps when needed.

C4/S4s may be the last of the Audis that can be considered for ease of owner maintenance. As the new cars increase with technology, it becomes increasingly complicated to diagnose repair without the proper tools. There is a cool program for a PC laptop that will read all of the fault codes and reset the computers. You still need skill for the repair.

So here we are at 200k. What shape is the car in? Oil consumption is about one quart per 2K. A little smoke blows out the back when the car is cold, and we think it is time for the turbo to be rebuilt. The body is tight and handles well. Driver's seat needs reupholstering. Pearl White paint is in great shape. It really feels like the '93 can be driven for another 100Kmiles with just normal service. I am completely satisfied with this car (and the '94), and my son enjoys driving it every day. Practical hot rod if there ever was one. He can fit a 4-12" speaker cabinet and an amp head in the trunk, two guitars in the back seat and a band mate or two as well. I also have enjoyed watching the resale value stay strong. I hope to write again when this '93 hits 300K.
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Old 12-25-2006, 09:30 PM
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Old 12-25-2006, 09:58 PM
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<b>Definition of FTL:</b>
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