M271 Ecu failure

[Rustyboy780]

Hi everyone. I thought i had previously posted on this problem but can now not find the thread. I don't know if it was removed or i just dreamed i had posted it. So excuse me if i'm repeating myself or posting in the wrong area.

I have a ongoing problem with my c200 Kompressor. It previously failed the MOT on the emissions test. It was running rich. I substituted the ECU and this solved the problem. The injector pulse time at idle was 3ms! But then i has no Odometer and only one key.So i splashed the cash and had a new ECU fitted at the dealer. 400 miles later it developed the same fault. (High emissions and P0172 self adaptation of mixture formation The mixture is too rich) I then put the second hand unit back on and 600 miles later that too has failed. Obviously something is causing the failure. Can anyone help?

Rustyboy

 

[grober]

There will be many sensors which will effect mixture formation. The ECU is capable of self adaptation so I can only assume after running a bit it goes out of range and flags a fault. Because the fault is common to 2 ECU's it points to some external sensor problem rather than the ECU itself.
likely causes can be any of the following
- Faulty front heated oxygen sensor - Ignition misfiring - Faulty fuel injectors - Exhaust gas leaks - Incorrect fuel pressure - Faulty Mass Air Flow (MAF) sensor

Read more: https://www.autocodes.com/qa/31999/self-adaptation-of-mixture-formation-p0172

Try cleaning the MAF gently with solvent first. If the engine/turbo is worn it may be blowing oil vapour onto the MAF sensor element?

 

[Lyserman]

I had a similar problem with my M271 engine.
Had to change a couple of connectors on the socket that connects to the ecu as they were not connecting properly with the pin on the ecu.
Try this:
Remove the cover from the ecu connector to expose the wiring.
Run the engine with an exhaust gas analyser and wiggle the wires individually to see if you get an instant improvement in the mixture. If I remember rightly the offending wire was near the end closest to the rear of the car.

That, combined with a faulty brand new MB O2 sensor took a while to resolve.

The O2 sensor was producing a transposed signal, ie -ve instead of +ve.
You could see the signal from the sensor on Star. So it would be worthwhile getting live data by hooking it up to a Star machine.
Got my money back from MB and bought the Bosch equivalent at half the price. Exactly the same sensor, just did not have a 3 pointed star engraved on it.

Here is a link to my original threads:
https://www.mbclub.co.uk/forums/engine/165124-c180k-p0137-p0172.html

https://www.mbclub.co.uk/forums/engine/165487-p0137-back.html