blacke30

Hello,

I'm new to the forums. I'm about to close a deal on a 95 S6 that my boss wants to get rid of. The problem is, that the car is running only on 4 cylinders. We have tried to change everything from coils to ignition modules.

Could it be the ECU? I can't think of anything else that would be wrong with it other than a ECU or possibly a cam sensor.

I'm a BMW guy, and the only other Audi I have owned was a Coupe Quattro, and oddly that one had a misfire too.

Thanks for the help in advance.
-PJ

Paul Heneghan

Remove the coilpack cover and spark plugs. Reinsert spark plugs into connectors and lay the assembly on top of the engine making sure the bodies of the plugs touch grounded metal. Remove FP relay and then have an assitant turn on the ignition and operate the starter. Observe presence or absence of spark. If you have access to a spark plug tester (device with a variable gap), then you can check for a weak spark as well.

If one spark is missing, then swap the two Power Output Stages over (if the cables don't reach, you might need to remove them from the metal bracket and put them back the other way around). If the fault hasn't changed the POSs are probably OK (they are the most common cause of one cylinder misfiring continuously).

Next step would be to try a known good replacement coilpack.

After that, you should probably test for continuity and no shorts on the wire from the ECU to the POS. If it turns out to be the ECU, there are a couple of people around who specialise in S6 ECUs - search here and the s-car-list.

Of course, if you discover that all five spark plugs are sparking beautifully, then you're looking at a fuel or compression problem for that cylinder.

Good hunting!

Paul

scarman

I can imagine your boss wanting to get rid of a problem he can't fix, but it is not clear why exactly you want the problem.

I really have not seen any of these type deals turning out well. You are really under the gun to quickly learn the systems just to get the car running. Is it really such a great vehicle that you can't pass it up?

Do you know if there are any DTCs (trouble codes) ? From your post it appears that one cylinder does not fire at all, correct? I assume you know which one and are prepared to share that information? The sensors do not record misfires in the ignition so there is probably not any direct help in the DTCs, other than their absence may help. There may also be some others caused by the misfire rather than the cause itself, but you need to be aware that they exist and they can be of some help.

This booklet has a good overview of the system; just separate the V8 and 5cyl parts:

http://12v.org/urs/VAG143AANMotronic.pdf

blacke30

I work at what you can call a German car junk yard. We work on anything from Mercedes down to VWs, Audis and BMWs.

We have checked for spark, and number 3 is not getting spark at all. I'm getting fuel, and compression is good across the board.

I'm guessing Power output stages are the little electric boards mounted on the firewall with white plugs on them? We put brand new ones on but to no avail.

We have also changed the coil packs with good working ones and still no spark.

We haven't checked the continuity from the ECU POS yet. Will do that tomorrow or sometime soon when I have time.


The car is in a decent condition other than the misfire issue. My boss gave me the idea of buying this car since I will be selling my MK2 soon and from what I'm looking at, these cars are not that hard to make power with.

If it wasn't such trouble to set up a Mega Squirt on this car, I would've had had my mind made up already.

Thanks for the help.

UrS4boy

Here is a post that contains coil and POS info including diagnostics and how to access the spare channel (for you, this might be swapping the POS connectors in pairs).

Click HERE

scarman

Besides the fun of making power, they are some of the most comfortable high speed road cars made.

The POS are the two ignition modules, probably black in color that has one set of black plugs from coils 1,2,&3 and brown connectors from coils 4 &5 and matching connectors on the other end to the ECU.

The white plugs are power to the coils. You might try switching those connectors to see if the dead coil changes, similar to the procedure provided for checking the POS. This would verify input power to the coil.

Since you mentioned changing coils, I didn't bother with the obvious issue of coil wiring itself. The wiring exit from the rear of the coil pack is subject to damaging the insulation and shorting these wires.