forum.audiv8.com Foren English Audi V8 Forum V8 engine trouble

Hello all Audi fans. I've been visiting this site for over a year but due to my limited technical knowledge this is the first time I am posting a message.
For more than 2 years I have been driving a 1990 V8 without any major problem. The car is a pleasure to drive even during the harsh winter months -I live in Calgary, Canada.
About two weeks ago I noticed that the car was not responding anymore to hard or full throttle acceleration. The power delivery is smooth untill 2800-3000 RPM, when the car starts shaking and blowing back in the exhaust system.
The problem has not been resolved by changing the oxygen sensor, spark plugs and air filter. Timing belt was changed 2-3 months ago. The only other problem I can relate this to is the fact that the car starts fine when engine is cold but requires a long key when engine is warm and left more than 20-30 minutes, which makes me suspect some problems with the fuel pump. I have disconnected the oxigen sensor based on some information from the web and the car didn't change its behaviour. The mileage on the car is 170.000 kms. I will take the car to my mechanic first and then to the Audi dealer if he can't fix it. Meanwhile, any suggestion will be appreciated.
Thank you,
Florin

I have a 1990 Audi V8 and my car is having similar symptoms. My car has little acceleration and idles extremely rough too. It feels like I am only running on half the cylinders. Any time I give the car gas it chugs and sputters like the TPS is failing. Timing belt was replaced about 2 years ago and O2 sensor 1 year ago. I replaced the OSV and am still stumped...

I am thinking that the base timing is not correct, TPS, or the fuel pump is failing on me.

Hello,

A couple other things you should look for is.

TPS - Throttle Position sensor
FPR - Fuel pressure regulator
Temp Sensor

Leaky injectors is another comon problem.
Spark plug wires

First thing you should do is have all the codes read. Most VW/Audi repair places has the VAG 1551/1552 scan tool if not you can do it by your self. Have this done first before getting too deep into replacing everything.

http://www.sjmautotechnik.com/ecufv8.html

That should help.

Another good source for info is from:

http://www.audifans.com/

Hope this helps,

Karl K

Thank you for the suggestions. I've been on vacation for two weeks but just before I left my mechanic checked the fault codes and he got code 2411 that sends us to the RPM sensor, injector sensor and a missing flywheel tooth. He told me that another customer had a simmilar problem and the symptoms were the same. In that case it was a missing tooth on the flywheel. Next week I'll check the flywheel. As soon as I find and fix the problem I'll post it here.
Thank you again.
Florin

How can a tooth be missing?? It seems more logical for me if the rpm sensor is faulty. If the rpm sensor is faulty not all tooth is caunted by the rpm sensor and it's effect is the same as a missing tooth. Just try to replace the rpm sensor which is not so difficult instead of replacing the flywheel which you have to remove the whole gearbox.

A tooth on the flywheel can be broken by the starter during start-up. Since I need a long key for start-up when the engine is hot(leaking injectors?) that seemed very possible. The first thing we've done was to reverse the two RPM sensors but the car behaved the same. My mechanic tells me that the car would not run with a faulty sensor. Then we checked the flywheel through the small window where the sensors are located and we discovered two teeth that are broken (about one third of the height), both having a fresh cutline. I decided to go ahead with replacing the flywheel on Sept.23rd. I do agree that replacing the sensors first makes sense if you try to find the problem by the method of elimination but my mechanic suggests that the RPM sensors are OK. I will let you know as soon as we get the job done.
Thank you,
Florin