Disabled LTFT's, good or bad? or neither?

[rel3rd]

Normally, I only have my LTFT's enabled while tuning VE. Have them disabled while doing MAF tuning and after tuning is done. Never an issue with WOT PE/AFR that way, obviously, but aside from VE tuning, for what other reason should I keep them enabled?

I had to richen up the tune a bit since adding a 4" intake tube to take advantage of the room I have after doing an electric fan conversion. It wasn't way off, but I did some tweaking anyway. Right now my LTFT's are + or -3 or less, MAF is 1% or less, and STFT's are generally + or -2 or less.

Is there any disadvantage to having the LTFT's disabled?

[Frenchy]

I had issues with my truck running uber-rich until it went into closed loop.

[rel3rd]

anyone?

[farmtruc]

I had issues with my truck running uber-rich until it went into closed loop.

If your truck was running rich in open loop (cold and initial start up), there are two tables for that. Once it went into closed loop, the pcm was given feedback by the o2's, which in turn, the ltrims probably got mroe and more negative until the pcm was satisfied by the o2 values.
That's one reason keep ltft's enabled.

anyone?

I like to keep them enabled and always do, they indicate a need to add or subtract fuel. I can't think of a reason to shut them off, so keep them on.
We may be able extract more power from our trucks and finely tune them, but that's not because the GM engineers can't tune don't have reasons for what they do.

Short trims don't always tell you if your truck needs more or less fuel over time, the ltrims do that.
I see a lot of scans that indicate strims are right one, but take a look at ltrims, they can still be way off.

[rel3rd]

Thanks for the reply. I turned them back on.

[raptors_67]

Fuel trims are ignored when in PE since the stock O2's can't give an accurate reading at those AFR's. Not running them may affect fuel mileage or if your fueling is out all the way across your tables there is a potential for running lean. LTFT's adjust fueling across multiple cells which the short term trims cannot do. I'd be more concerned with the need to run with them off than leaving them on as they are a great indication of fueling not being dialed in properly.

[farmtruc]

Fuel trims are ignored when in PE ...may affect fuel mileage or if your fueling is out all the way across your tables there is a potential for running lean..

Just to clarify, they are ignored, but kind of not. If ltrims are positive, this indicates the pcm is adding fuel to compensate for a lean condition. Therefore, there is no longer a lean condition.
If ltrims are positive during PE /WOT, the pcm is adding fuel, therefore, skewing actual a/f ratio. Ltrims should be negative before the pcm enters PE mode.

Just adding to what you already said.

[pl4yboy]

I'm not quite sure why you would want to disable them anyway. They're good information to have.

[raptors_67]

Just to clarify, they are ignored, but kind of not. If ltrims are positive, this indicates the pcm is adding fuel to compensate for a lean condition. Therefore, there is no longer a lean condition.
If ltrims are positive during PE /WOT, the pcm is adding fuel, therefore, skewing actual a/f ratio. Ltrims should be negative before the pcm enters PE mode.

Just adding to what you already said.

I don't have as much experience with LS series stuff as other GM vehicles, but if i remember correctly i have always seen the LTFT 0 out at WOT.... i think that is also the case on the few LS vehicles i've done as well but i dont recall 100%. Would i be wrong in thinking this?

[farmtruc]

I don't have as much experience with LS series stuff as other GM vehicles, but if i remember correctly i have always seen the LTFT 0 out at WOT.... i think that is also the case on the few LS vehicles i've done as well but i dont recall 100%. Would i be wrong in thinking this?

If the ltrims are negative during normal driving and non PE, then they will go to zero at wot. If they are positive during non PE, they will be positive during wot as well.
When this happens, the pcm will add fuel during wot because it thinks there is a lean condition.
If they are negative during normal driving and goto zero at wot/PE, then the pcm isn't adding any additional fuel.

This is why one of the first things I tune are ltrims. IF they are positive during normal driving and wot/PE, then actual a/f ratio is off due to the pcm adding fuel.