Hi

This car runs rough occaisionaly, it has had a lot of people looking at it in the past so I am unsure of what I have taken on!

The ECU has been replacred with a 728 ECU because the keys were lost, I have since put the original ECU back on and realigned the EWS. Since then the car runs better, but runs rough every now and again. It has had a replacement AFM and O2 sensors. The O2 sensors show a fixed reading of 4.71v and 4.83v and the DTCs are 203 'O2 sensor limit cyl 4-6' 202 'O2 sensor limit cyl 1-3'

The O2 sensors have Yellow,White,Red and Black wires, could they be the wrong O2 sensors? I know they use Seimans and Bosch but I am not sure which ones this car should use.

Sorry for the long post

Simon

Simon
it has had a lot of people looking at it in the past so I am unsure of what I have taken on!

I know what you mean it's like startrek but in reverse, you are boldly going where every inadequate 5/8 has been before

E39 is a 5 series so I'm unsure what car you have.
Please clarify if it's a 3 series or a 5 series and the engine capacity.
Exhaust gas readings would also be helpful to figure if it's really running rich.

Gerard

Hi
Sorry for the typo. It is an E39 1997 523i M52 MS41.0. I am afraid no gas readings! If I add more air into the system or hydrocarbens the is no change in the O2 sensor readings.

Simon

Simon

You have a can of worms here but you know that..

Taking what you say at face value, it looks like the O2 sensors are both u/s. However, I would get a gas reading done before going any further to try determine what is happening in the engine. You really need to know what's coming out that exhaust.

Gerard

Hi

I checked the O2 sensors with the other type [not sure which was which!] The right ones are fitted.

My mistake with this car is the O2 sensors read a high voltage when lean low when rich, I was looking at it with the view it had a rich mixture. However, one I relaised I managed to trace the fault to a corroded crank case breather pipe drawing in air [not much, but enough!] After replacing the pipe and resetting the adaption values the O2 sensors were switching as they should and car running well.

Many thanks for your input.

Regards

Simon

Hi Simon

Well done on getting it sorted.

I must admit that the Siemens aspect hadn't registered with me either but a gas test would have quickly set the thinking muscle in gear and the penny would have dropped.

One strange aspect of the job is that your test to enrich the mixture didn't cause a flicker in the sensors. It must have been a bigger air leak than it appeared.

Gerard