Fuel Trims on a 2.2 Ecotec

[Admiral Jedi]

From a Jbody ecm.

I have a histogram set up to monitor my fuel trims so I can make changes to my pe tables instead of using the wideband, they seem to be less extreme and make the car happier instead of choppier.

I'm only monitoring Short Term Fuel Trims and making the changes to the VE table according to those. My question is this: Do the Short Term and Long Term add together to make the total fuel trim? Say my STFT is 3% and my LTFT is 4% in any one cell. Would I have to add a total of 7% to make the full correction in my VE table, or will the 3% do it?

I hope that makes sense.

[Iam Broke]

Not familiar with your setup, but the LTFT's & STFT's sum in the LNF's so I would think that is the case with yours. Never offset all at once though, If they add to +7%, I'd prob multiply by 1.04 or 1.05 to start off. Someone more knowlegable than I will post though.

[oldskool]

I would try to work the LTFT's to -2 or so. The STFT's are always going to be a moving target on our car. I've found a HUGE difference in AFR going from summer to winter (~1.5:1!!).

If we had the fueling IAT multipliers available, we might be able to tune once and leave it, but to keep it dead on, you'll need a re-tune with the seasons. Or find a happy average temperature and deal with rich in the summer and lean in the winter

[Admiral Jedi]

I'll give that a try. Thanks for the tip.

[HawkZ28]

If in the same cell, you have an LTFT of -3, and a STFT of +4, you'd want to mult - 1/2 by the -3, and then mult - 1/2 the +4. That is what (on average) the computer is already pulling/adding to acheive lambda.

If you can disable the LTFT and tune off of STFT, it's a LOT faster/easier. You shouldn't tune off STFT alone when your LTFT are enabled- you are only getting part of the puzzle that way.

I wouldn't tune your PE tables with the NB either...are you positive the histo for the WB is set up correctly- maybe it's a voltage offset or something messing it up....? The NB's just aren't accurate at anything other than lambda 1.

Also, don't forget to reset your trims with the scanner (if capability is there with your PCM) before you start logging again.

Hope that helps you out

[Admiral Jedi]

I thought I would update the thread. I've been using a histogram I set up that adds LTFT and STFT together, then adding half the change to the ve tables. I've done it twice and the car is a LOT more responsive. Thanks for the help!