1990 V8 Starts Cold, Not Hot -- Help, Please! [Archive] - Audi Forums

: 1990 V8 Starts Cold, Not Hot -- Help, Please!

12-23-2008, 11:11 AM
My 1990 V8 (auto trans) was running beautifully and dependably until about a month ago. It began to become harder and harder to start when warm, until it would only start when cold. An hour after shut down, it would not start. Wait another 30 minutes and it started easily. My mechanic says it has no fuel and no spark when warm. He has tested the crank sensor and cam sensor and these are good. He says he can't read diagnostic trouble codes because of the aftermarket radio. He is almost (but not quite) as frustrated as I am. If it doesn't start by Monday, it is off to the dealer... and I really don't want to end up replacing the control module if avoidable!

Help is much appreciated!

04-05-2009, 09:46 AM
Check the rpm sensor. Crank the engine and see if the tach bounce, no bounce then replace the rpm sensor. In order for the ECU to send a trigger signal to the coil it needs, crank timing signal, and rpm signal. The ecu will prime the fuel system when you first try to start the engine, but will not supply the signal to the fuel pump relay until the engine has started. The cam sensor is in the right distributor, but is not needed to start the engine, but will cause a performance problem if it is not functioning correctly.