Fuel Trim and Lambda Pre Cat o2

[neilr]

Hi All,

My first post - I recently acquired a project A2 1.4 bby and have complete a general refresh of the the motor and bodywork.

I am having a challenge however with emissions & fuel trims. I have changed:
MAP & pre cat o2.
Oil separator.
Spark plugs.
Fuel and air filters.
and checked all the piping for air leaks.

I have also completed:
Egr clean and reset adaption.
Likewise for throttlebody.
Injector clean and test.
Checked coils.
Fuel pressure test.

My sense is their is some sort of signal or voltage issue having discounted all the above.
The resistance on the wiring from the pre cat o2 to the ecu harness seems ok.
One oddity - the connector is receiving 10.4 volts to pin 5 of the sensors connector. The heater voltage is through pin 2 and this is fine.
Pin 5 ties in with socket 70 of the ecu and I have back probed it and the ecu is putting out the 10.4 volts - its not a short within the wiring.

I have searched high a low for voltage specs from the ECU but cannot find. I have wiring diagrams but cannot seem to identify the voltage.

Is there a history of ECU and o2 sensor problems on these BBY engines.

Any guidance would be greatly appreciated!

I have also posted same on the German forum.

Thank you.
Neil

 

[steve_c]

Welcome to the forum, Neil.

I can see that you've already replaced the G39 lambda probe - what make of probe did you fit?

 

[neilr]

Hi Steve,

Thank you!
I replaced with a like for like NTK.
The output on fuel trims remained same with the old and new.
Bias voltage is my train of thought now. When I disconnect the O2 the car idles fine.

Best
Neil

 

[steve_c]

You need expertise that I am afraid is beyond me. I don't know if @timmus would be able to offer any advice here?

 

[neilr]

Thank you Steve!

@timmus any pointers would be greatly appreciated.

 

[neilr]

@steve_c @timmus

Just in case you guys comes across a similar case. I was experiencing 60+ long term fuel trims on the bby. I changed all sensors etc. I ended up doing a top end rebuild - exhaust valves and stem seals were in very bad shape, timing may have been out also.

Car now running LTF of +2/3%

Best regards
Neil