rich idle

[tricguy007]

Ok been trying to figure this out. My fuel trims at idle long term is -14 then I barely touch the gas and it goes to 0 then while crusing it goes to -3, full throttle pull it hits between 3 and -3 have lost a some power but does hit rev limiter. Tried diconnecting the evap line and capped the tb connection, no fuel at the pressure reg.,tune up and tb cleaned about 5 k ago, at idle o2 goes from around 800mv and drops to around 100mv then back but on a full throttle pull it goes 300mv to 700mv, the truck is all stock drivetrain this is with a tech2 scanner already reflashed with the latest calibration. Any help please !!!!!!

 

[The_Roadie]

Long term trim is smoothed deliberately to allow the short term trim to control AFR. What's your short term data saying? What's your AFR saying? If you're seeing the proper 1-2 Hz bouncing in the O2 sensor raw data, then it's OK, but it should also bounce up and down quickly at a steady but higher throttle.

Eric - you reading this thread?

 

[tricguy007]

My afr says 14.6-1 and my short term is usually around + or - 3 with my long at -13to -14

 

[tricguy007]

What I've always learned is your long term should always stay between 10 to -10 or u may have an issue

 

[CaptainXL]

What I've always learned is your long term should always stay between 10 to -10 or u may have an issue

A normal STFT reading will generally fluctuate between negative and positive single digits 2-3 times per second. Usually they'll stay around positive or negative 5%, but they may occasionally go up towards 8 or 9% depending on the efficiency of the engine, age of the components, and other factors. A normal long term fuel trim reading will appear to stay the same, giving a long term average of fuel added. It, too, should be close to zero, positive or negative single digits under normal circumstances. It will fluctuate much slower, possibly appearing static.

http://www.obd-codes.com/faq/fuel-trims.php

 

[MAY03LT]

Do you still have access to the tech2?

 

[tricguy007]

Yup except on the weekend

 

[limequat]

Check for vacuum leaks

 

[tricguy007]

Wouldn't a vacuum leak cause positive fuel trims not negitive. Wondering if my cat isn't partly pluged,

 

[CaptainXL]

Wouldn't a vacuum leak cause positive fuel trims not negitive. Wondering if my cat isn't partly pluged,

Yes. The LTFT would be up in the positive for a vacuum leak. Stuck injector(s) could give you a negative LTFT. STFT would still reset after the LTFT has been bumped and read between +5 and -5 %

 

[MAY03LT]

Tried diconnecting the evap line and capped the tb connection, no fuel at the pressure reg.

Did you get those tests from the p0172 flow chart? The last test in that step was the injector balance test. With the tech2 and a pressure gauge, that is a super easy way to confirm a sticky/leaky injector. You're not running rich enough to set a p0172 (trims would have to be -35) but those tests are addressing the same thing.

The flow chart also states that an intake restriction would cause this, but I'd expect a driveability problem if that was the case.

One thing that isn't in the P0172 test, I had an I6 Envoy that had a skewed MAP sensor that was causing the trims to go negative. I read a tech tip which said to compare the MAP reading to a "known good" I6, and sure enough it was off.