Calling all fuel trim experts!

Hey guys,

I've been chasing a fuel trim issue for quite some time and need some expert help. I'm including a lot of data, so hopefully it will accelerate and narrow the areas of investigation.

The facts:

1999 E36 M3(not an e46, but the same basic rules apply), 96k miles, Supercharged via AA Twin-screw (9lb psi), stock exhaust

-O2, MAF, Fuel filter and regulator replaced 1 year ago
-Spark plugs and fuel injectors replaced a few weeks ago
-Car throws 1188/1189 codes (fuel trim) consistently after a few "trips"
-Plugging in an OBDII data logger shows positive fuel trim(10% - %20+) all the way from idle, hard acceleration and cruising speed.
-Car has had supercharger for 4 years now and initially had trim issues when first installed(vacuum leak), but has run fine since for 2 solid years without issue
-Car is showing larger positive trim at cruising speed, not at idle (the latter usually indicates a vacuum leak as vacuum is larger at idle)
-Car shows no physical signs of issues (i.e. no limping, hesitation on acceleration, nor rough idle)

I just need some direction on where to go next since these codes are preventing a successful smog check (resetting the ECU doesn't work because the "monitors" in the ECU will reset). This is really looking like a vacuum leak issue (which, at this point, is going to require a smoke test because I've been over every hose and seal a million times), but I wanted to make sure if this is possibly pointing to a fuel pump failing or another MAF issue.

I'm hyperlinking graphs of a 5 mile trip that show values of short term fuel trim for both banks at different RPM/Throttle Position plot points AND MAF volume reports at the same plot points. (note that idle is at around 800 RPM and 15% Throttle angle and cruising speed is 3200 RPM and %30 Throttle Angle) On top of that, I also have a link that shows the same trip, but in a line graph showing the same values in a different way. Note that I've reset the adaptations to start off fresh and that's why the Long Term Fuel Trims are small (they WILL grow to %12 percent if I drive long enough).

I need someone to take a look and see if there's a definite smoking gun here so I don't blindly go and check a bunch of other things unnecessarily.

I'm trying to be as thorough here for you guys as much as possible, but let me know if I've missed anything.


Table of STFT and MAF readings

Graph of data (for the same trip)

Thanks!

Kazam

whatever was wrong with his car is probably wrong with mine too. the situation looks very similar.....his throttle angle at idle seems high.

Originally Posted by glhx

whatever was wrong with his car is probably wrong with mine too. the situation looks very similar.....his throttle angle at idle seems high.

Hey, I neglected to update this thread, but after sending this data off to Active Autowerke (the mfr of the supercharger) soon after my OP, they realized that there was an issue with the existing MAF/calibrator and ECU programming. I got a new MAF that didn't require a calibrator and an update to my ECU. Since then, all has cleared up and I passed CA smog.

I got a lot of feedback on other forums, but the data captured was invaluable in convincing AA something was wrong with their system.

Someone call for a trim expert?!

if you have access to more data. can you confirm what throttle position is at idle. I keep seeing that 0% from other people....but you posted 15%.


Mine is at 10%

we are thinking my problem is the maf sensor but we are unsure.

my ltft are 11.7 on both banks
my short term fuel trims are fine/.....a lot like the situation you had

alex......we are calling you.....your the fuel trim expert and ladies man...... the ladies man should be expert in all forms of trim

And you passed ca smog. I remember those days when I was out there. They takes emissions seriously.......way too seriously