Stealership Won't Fix Ltft's

krww06 · July 16, 2009

I have an '07 GMT-900 and had was in the process of getting a tune by Justin. However, after I ran my initial datalog(s), Justin commented that my LTFT's didn't look quite right. Both banks were reading about the same percentages, however the percentages are dropping as low as -22% and "averaging" about -7%. The Factory Service Manual says the LTFT's should be "near 0%," and after doing a lot of research and consulting with some knowledgeable friends of mine, we are all in agreement that consistently having double digit trims is not how it should be.

Anyway, I took it to the stealership to get them to fix it, and as I had anticipated/feared, they said it was fine. Their main rational was that since it wasn't throwing a code it was operating as GM intended. I know that something isn't operating exactly like it should (after all, if everything was, then I'd be w/in a couple of % points of zero), but due to the number of variables that could cause my LTFT's to be off, the dealership won't exert the effort to figure out what's causing it. Does anyone have any recommendations/advice for getting the Stealership to fix this, or what in particular I might get them to focus on (e.g. TPS, MAF, MAP, etc.) as it IS going back for them to look again?

BTW, I do not want to try and tune "around" this issue and Justin agrees that it would be best not to either. TIA.

DBVille · July 16, 2009

Although they are low, no code, they won't fix it, unless you can some how identify something to fix. I doubt they understand LTFTs well enough to know where to look, without a code. What do you expect them to do - start changing parts to see if it gets fixed? You don't have any symptoms. It is possible that everything lined up to where you run that way.

Do you have any mods? Taken anything apart? Low FTs should mean, if I am thinking straight, low air flow compared to the MAF, or a rich O2 signal. How does it run? Any signs of it running lean?

V8nuts · July 17, 2009

The dealership will charge you $100 per hour to have some kid who just got out of school to guess what is going on in your truck. I only let them touch my truck when there is no other solution.

nbscanuck · July 17, 2009

any intake leaks, exhaust leaks?

Draenor · July 17, 2009

The neg trims, means it is pulling fuel, not adding. Have access to a wideband? If so datalog with it. If there are sharp spikes in when the trims start pulling back, my guess is the O2 sensor. If it is a broad sweep in fluctuations, then it would be one of the other metering devices, MAP,MAF,etc. Since it is trying to cut fuel, it means your not getting enough air....Or the FPR is not holding steady and letting in too much fuel. You can check you PSI with a guage at the rails.

Have you done any mods to the intake/ehaust? Is the airfilter clean?

krww06 · July 17, 2009

Do you have any mods? Taken anything apart? Low FTs should mean, if I am thinking straight, low air flow compared to the MAF, or a rich O2 signal. How does it run? Any signs of it running lean?

At one time I had the GMPP intake on, but after my first unexpected LTFT datalog, I reinstalled the OEM intake, just to compare. The OEM intake produced results that were "closer" to 0%, but they weren't significantly different.

It does have a really rough, almost violent idle at times (usually either when it's cold or after being driven hard). It feels/sounds as if it's missing when it gets to this point. However, the dealership pulled out a TSB claiming this was normal. I still don't buy this, but that's neither here nor there.

It's also got an issue where the idle will jump up unexpectedly (e.g. when slowing down to a stop or near stop) that might or might not be related to the LTFT issue. Anyway, you'll have your foot on the brake and be coasting or slowing down with the RPM's in the 600 range as they should be, and then for no apparent reason it will surge up to 800-900RPM's. It is a strong enough surge to overpower the brake. It'll get your attention really fast, b/c if you don't nail the brake hard, you are crashing into what's in front of you. The dealership claimed this was normal too and that they had a TSB as evidence. However, when I told them I wanted a copy of the TSB, guess what, they couldn't produce one.

any intake leaks, exhaust leaks?

None that I'm aware of, and yes the air filter is clean.

The neg trims, means it is pulling fuel, not adding. Have access to a wideband? If so datalog with it. If there are sharp spikes in when the trims start pulling back, my guess is the O2 sensor. If it is a broad sweep in fluctuations, then it would be one of the other metering devices, MAP,MAF,etc. Since it is trying to cut fuel, it means your not getting enough air....Or the FPR is not holding steady and letting in too much fuel. You can check you PSI with a guage at the rails.

Have you done any mods to the intake/ehaust? Is the airfilter clean?

I'll look into those suggestions as well.

Draenor · July 17, 2009

It does have a really rough, almost violent idle at times (usually either when it's cold or after being driven hard). It feels/sounds as if it's missing when it gets to this point. However, the dealership pulled out a TSB claiming this was normal. I still don't buy this, but that's neither here nor there.

It's also got an issue where the idle will jump up unexpectedly (e.g. when slowing down to a stop or near stop) that might or might not be related to the LTFT issue. Anyway, you'll have your foot on the brake and be coasting or slowing down with the RPM's in the 600 range as they should be, and then for no apparent reason it will surge up to 800-900RPM's. It is a strong enough surge to overpower the brake. It'll get your attention really fast, b/c if you don't nail the brake hard, you are crashing into what's in front of you. The dealership claimed this was normal too and that they had a TSB as evidence. However, when I told them I wanted a copy of the TSB, guess what, they couldn't produce one.

Neither instance a DTC was set? (Check engine light) For the Idle problem, try cleaning out the throttle body, the vortec motors ar know to carbon up the backside of the TB. A good cleaning may fix the idle problem. My only other gues is the TCC isnt unlocking correctly.