fuel trims levels all over the place
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 496
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From: GARDEN GROVE, CA
fuel trims levels all over the place They go at part throttel and wot negative to positive. For instance at part throttle looking at my predator tuner in live data the top LT with show negative one second and then positive and this happens with both LT's. At wot one will show positive and the other will be at 0 which I know 0 is what you want but then the next time at wot both LT's might go to 0 and then the next time the other LT with show 0 and the other one postive. My cars power is way down too. Ignore my signature as far as mods go. I have been running with the stock airlid, maf and tune for many months now. Could a vacum leak cause this or a bad maf? IF I unplug the maf the car runs stronger.
Well, how far positive are we talking about +1 or 2 or 3 or -1 or 2 or 3 is not too bad really. Unplugging the maf puts it into SD mode and you will run off the VE tables...might feel better, but could be unsafe. Check that your maf is clean and the resistors look intact. Descreened? How are your 02 sensors?
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 496
Likes: 0
From: GARDEN GROVE, CA
Another thing to point out is my idle is weird. I have a vacuum gauge on my I-pillar and it varies on when it reads when at idle. I had a problem with the car idling a little low when pulling up to a stoplight and then I would hear the motor rev up a bit and the idle would go up and stay there. It mostly went away after I changed the fuel filter a few weeks ago.
Vacuum leaks can lead to surging and low-airflow positive
trimming. It would have to be a hell of a leak to affect
mid throttle.
Your trims will bounce about, based on the fuel trim cell
you are in. The fuel trim cell setup on your car is stupid,
Cell 0/4/8/12 has to cover idle to 2500RPM, cell 1/5/9/13
has 2500-6500 and the other 8 are not accessible. That
means one lonely little trim value has to cover 2 octaves
of RPM, the RPM variation in airflow / exhaust temp, and
a volumetric efficiency that swings big time as well. Yeah.
Sound likely to work? That's where you pick up a driving
history effect, trims that drift up and down over minutes
to hours, trip to trip.
trimming. It would have to be a hell of a leak to affect
mid throttle.
Your trims will bounce about, based on the fuel trim cell
you are in. The fuel trim cell setup on your car is stupid,
Cell 0/4/8/12 has to cover idle to 2500RPM, cell 1/5/9/13
has 2500-6500 and the other 8 are not accessible. That
means one lonely little trim value has to cover 2 octaves
of RPM, the RPM variation in airflow / exhaust temp, and
a volumetric efficiency that swings big time as well. Yeah.
Sound likely to work? That's where you pick up a driving
history effect, trims that drift up and down over minutes
to hours, trip to trip.
Originally Posted by jimmyblue
The fuel trim cell setup on your car is stupid,
Cell 0/4/8/12 has to cover idle to 2500RPM, cell 1/5/9/13
has 2500-6500 and the other 8 are not accessible. That
means one lonely little trim value has to cover 2 octaves
of RPM, the RPM variation in airflow / exhaust temp, and
a volumetric efficiency that swings big time as well. Yeah.
Sound likely to work? That's where you pick up a driving
history effect, trims that drift up and down over minutes
to hours, trip to trip.
Cell 0/4/8/12 has to cover idle to 2500RPM, cell 1/5/9/13
has 2500-6500 and the other 8 are not accessible. That
means one lonely little trim value has to cover 2 octaves
of RPM, the RPM variation in airflow / exhaust temp, and
a volumetric efficiency that swings big time as well. Yeah.
Sound likely to work? That's where you pick up a driving
history effect, trims that drift up and down over minutes
to hours, trip to trip.
Are you saying that there are not as many fuel trims cells as cells for the VE table? That fuel trim cell "resolution" is very pixelated and inaccurate????
Does that apply to both long term and short term?
Trending Topics
Fuel Trim Cell boundaries are adjustable but my year
and others have them set wastefully. You can put
them all in play and arrange them somewhat to make
the low fussy end more granular and leave only a
couple to be stepped on by PE/WOT. There are a few
good threads out there, for those with a functional
Search capability, that explain it visually. There are
only 16 closed loop off-idle trim cells. Some are just
not easy to hit in normal driving; the accel, cruise and
decel only hit a diagonal slice of the RPM, MAP space.
Here is something I drew up a while back, it's a mind
scrambler but dig it:
and others have them set wastefully. You can put
them all in play and arrange them somewhat to make
the low fussy end more granular and leave only a
couple to be stepped on by PE/WOT. There are a few
good threads out there, for those with a functional
Search capability, that explain it visually. There are
only 16 closed loop off-idle trim cells. Some are just
not easy to hit in normal driving; the accel, cruise and
decel only hit a diagonal slice of the RPM, MAP space.
Here is something I drew up a while back, it's a mind
scrambler but dig it:
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Bringing this one up from the dead a little...
I compared my 98 FT boundaries to a 2001 and 2002 file. There's a huge difference. Is there any practical reason GM would have set them this way on the newer models??
I compared my 98 FT boundaries to a 2001 and 2002 file. There's a huge difference. Is there any practical reason GM would have set them this way on the newer models??
