Hi,

Both oxygen sensors were replaced a couple of days ago on my Audi A4 1.8T 2001, but the car does not start after the engine is warm (it starts after applying the starter motor for a long time).

Symptoms:

1. I have to spin the engine with the starter motor for 30-40 seconds and several times, until ignition starts and even then the engine's rpm is only 500; then suddenly spins up and idles at 900 rpm.
2. However, the engine starts easily when the engine is cold.
2. The oxygen sensor output (Bank 1 Sensor 2) at cruising speeds is between 0.700 and 0.800 V (rich mixture).
3. The short term fuel trim (Bank 1 Sensor 2) is always constantly 99.2% (rich mixture).

I have the following questions:

a. What is the expected oxygen sensor output voltage at cruising speeds (2500-3000 rpm)?
b. What is the reason that the engine does not start after has been warmed up?

Could anyone please help me with some advice? Many thanks in advance.

 

Check your vacuum lines. Older cars they become very brittle and break easily.

.700 to .800 isn't extremely rich either.

 

Scan it and make sure their isn't a coolant temp sensor fault either

 

Thank you very much, Audi Tek. I will check them.

The problem I described started happening a day after the oxygen sensors were replaced, this is why I suspected that they might not be the right model or they are not installed correctly. Today I had to start the engine a number of times while being warm, it started well, except for one time when it took long rev-ing before slowly started working by itselfand the exhaust was dripping.

Only to make my learing curve steeper: how the vaccum lines are affecting the mixture. I guess, if the coolant temp. sensor is defective, it could sense that the engine is cold when actually is warm and the control unit keeps feeding it with rich mixture.