Hello all MB experts- I had the fuel trim malfunction code on my 95 C280 and I purchased a new MAF (from ******** in AZ
-$262) and installed it and cleared the codes by taking the battery cable off. The light stayed off for one whole day and came on the second day. I had it checked at AZ and I got the dreaded fuel trim malfunction- bank 1 message. The car had a lot more zip after I put the new MAF sensor on. Is it possible for the new MAF to go bad in one day ? I have read a lot about gas cap leaks- could this be the problem? I have no other codes showing. Should I reset it again by taking the cable off or should I have AZ reset it with their reader?
Thanks for your insight.

Larry

When you cleared the memory , you put the ECU back to normal. You assumed the MAA caused the adaptation numbers to trip the code.
Now , with a new AMM, the adaptation has gotten out of limit again.
Did you get a bad AMM, I doubt it.
More probable that your original condition was caused by a vac leak or a bad fuel pressure regulator.
That is why it is always recommended to check those first , before jumping to the AMM.
The reason Techs go with the AMM test , is b/c they have one to use as a test tool , saving time without spending $$ on a part. They can leave the bad adaptation memory , do a quick AMM swap, drive around the block a couple of times and watch for the adaptation to get back in line. [ confirming bad AMM]
But for DIYers, I always recommend [and so does AllData ] looking for vac and doing a fuel pressure test.
If you go back a couple of post that you posted on, read the one by Steve B. and MB Stars... they explain it to the T...
The reason your car ran better is b/c you cleared the memory back to normal. It was not the results of the new meter, but rather the proper/ short lived ECU mapping. Which has now gotten back out of limits.
As I said , you may have gotten a BAD meter, but I doubt it......

Thanks Arthur- I don't know what a "test AMM" is or where to get one. How does a DIYer get this done. I already paid hundreds of $ for the initial analysis that I needed a new MAF! Anything I could look for without the diagnostic tools mentioned ? Thanks!
Larry

L
I quess I was not clear on the "Test AMM"

What I mean is that one replaces the suspect AMM with a known GOOD one.
That now becomes a "TEST AMM TOOL "
It is just an easy way for quick diagnosis. Like changing a tail light bulb with a known good one to save the time of checking for voltage and ohmmeter-checking the bulb .
There is no AMM TEST TOOL. It is just a Tech trick of swapping the part with a known good one for testing purposes...
Techs usually have access to these, DIYers don't..
Unfortuately for diyers , AMM and MAF sensors are very hard to diagnose
without proper equipment..
But regulator test and looking around for vac leaks is easy and sometimes are the problem..

Thanks Arthur- I guess I already did the "test" when I installed the new MAF. How do I do a regulator test? Is there a chance the gas cap is still a possibility ?

Larry

I can't tell you what is wrong without another code retrieve, but I doubt it to be the gas cap.
You may want to take the vac. hose off the fuel pressure regulator and see if any evidence of gas/fuel in that line or at that port. That would be a diy test for bad diaphragm on the regualtor and that would cause your fuel trim code.
A better test would be a fuel pressure test. That requires a gage hook up and some specs.
Look everywhere for vac leaks...specially under the front engine cover at the SOVs..the line that feeds them is common fault as it is plastic and cracks from heat fatique..
Another one is the purge valve sticks open and causes a vac leak when not called for .. this one is hard to find b/c it is an internal leak and not seen or heard. If one suspecs that, it is usually coupled up with another purge code ... but not always
Diy trick here is to plug that line and run the car for a few miles to see if the trim codes clears itself.. it will bring up another code for purge, but you are expecting that code .
Scanner is pretty much a needed tool on all these 0BD2s, so you are not guessing..