Fuel trim and fuel pressure

[Eraser-X]

Hi guys I just went through the MAF errors P0170 and P0173 and replaced my MAF. The old MAF had my long term fuel trims at about 7 to 8% and the new MAF is giving me reading of -18%. I checked my fuel pressure and it is at about 58 psi or 4 bar. Is my fuel pressure too high or what else could be causing the computer to think the car is running rich? The car is a 02 E55 with 97K on it. Thanks

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[ProjectC55]

Originally Posted by Eraser-X

Hi guys I just went through the MAF errors P0170 and P0173 and replaced my MAF. The old MAF had my long term fuel trims at about 7 to 8% and the new MAF is giving me reading of -18%. I checked my fuel pressure and it is at about 58 psi or 4 bar. Is my fuel pressure too high or what else could be causing the computer to think the car is running rich?

The car is a 02 E55 with 97K on it.
Thanks

Have you replaced all of the O2 sensors? They do go bad on these cars. If u chg them chg all at ONE time!

[tbenz]

check the crank case ventilation system, ck that the seals on the air mass are in correctly, ck vacuum leaks, fuel press sounds good, you may need to just get the adaptation values reset with a scanner

[Ted Baldwin]

Originally Posted by Eraser-X

Hi guys I just went through the MAF errors P0170 and P0173 and replaced my MAF. The old MAF had my long term fuel trims at about 7 to 8% and the new MAF is giving me reading of -18%. I checked my fuel pressure and it is at about 58 psi or 4 bar. Is my fuel pressure too high or what else could be causing the computer to think the car is running rich?

The car is a 02 E55 with 97K on it.
Thanks

............Your long term fuel adaption is pretty bad. You probably have a bad CAT. What you want to do is to read pre and post CAT or sensor values to see if it is your or sensors or your CATs. I think the problem is one or more of your CATs. CATs are warrantied to 80K miles. An indy shop may first swap your or sensors because it is cheaper to do than changing your CAts, especially if it is the Right CAT.


Ted

[Eraser-X]

Thanks for all the quick responses.

I have gone through the all of the ventilation hoses and connections and eliminated all of the vacuum leaks. If I cause a vacuum leak the false air causes the long term trims to go positive. The trims are within less then 1% left to right.

I read about a dynamic test where you read the air flow on the MAF at full load and 4000 RPM but I have not found the test value in the WIS or the expected fuel pressures. Can someone post this info?

Once again my problem is the car wants to be RICH and the adaptives are LEANING it out the reverse of most of the MAF issues.

Thanks

[Ted Baldwin]

Originally Posted by Eraser-X

Thanks for all the quick responses.

I have gone through the all of the ventilation hoses and connections and eliminated all of the vacuum leaks. If I cause a vacuum leak the false air causes the long term trims to go positive. The trims are within less then 1% left to right.

I read about a dynamic test where you read the air flow on the MAF at full load and 4000 RPM but I have not found the test value in the WIS or the expected fuel pressures. Can someone post this info?

Once again my problem is the car wants to be RICH and the adaptives are LEANING it out the reverse of most of the MAF issues.

Thanks

.............You do not have a MAF issue. You are wasting your time on the MAF.

Ted

[Eraser-X]

Well guys got my hands on another MAF and was able to verify that it was a BAD MAF that was causing the issues. GermanStar took care of replacing the bad MAF very quickly and without any unneeded hassles.

I was not able to get the information I was looking for to complete the dynamic but I will keep looking for it and post it once I find it.

[amgalex]

Hey bringing this thread form the dead
but I got a power loss issue which is related to fuel trim, at wot my fuel trim goes to -23%
did yours had Negative fuel trim just on long term not at wot or what?