I was running a bit high on my LTRIMs, and for the first pass I bumped my injector adjustment factor by 5% to 1.39 having used 1.33 for SVO 30lb injectors on my first try. I was still rich and since I had also switched MAFs from stock (unported) to SLP 85mm (descreened), I decided to use bring the LTRims down using the MAF rate. I multiplied the entire table by 95 (5% reduction in mass read) and it brought some of LTRIMs down by 5%, but others only came down about 2 - 3%.

It did have a major effect on my O2s at WOT. They went from running around 940 - 970 down to 895 - 910. I only made a couple WOT runs after the change with only about 20 miles of driving. I'll see how stable it remains.

 

Ok, I'm really new to this computer tuning/programing, so I was wondering why you decreased the MAF rate for you're larger 85mm MAF sensor. I had read previously that if you had an aftermarket MAF, you would have to alter the MAF rate table before you could get your LTRIMS under control; however, I read that they INCREASED the whole table by 7-8% to compensate for the higher flow rate. Maybe I read wrong or that person was mistaken, but I was just wondering because when I do my cam this summer I'm going with LS1 edit and a larger MAF. Thanks.

- Matt

 

My LTRIMs were primarily in the -5 to -13 range. That means the base program was adding too much fuel and the computer was having to pull fuel through the LTRIMs. My solution was to tell the engine computer that less air was coming in for a given MAF reading. Less air = less fuel needed; therefore it lowered my LTRIMs.

It is possible that the SLP calibration in my MAF was off, or that my original tuning (for a different heads & cam package) needed to be tweaked for this set-up, or the correction for the injectors was a little low. Since I had a lot of variables change at once due to my engine swap, I can't pinpoint the source.

I found a cam swap to have less effect than cam + heads swap. No matter what the results, you can just as easily increase the MAF rate with Edit if that's what you need.