long trim out of spec

[smslyguy]

I have a 2000 gmc and i have notice that even the stock tunes long trim are all over the board all the way to +25 is this typical for a stock truck to have the trims this far off from the factory???? Was woundering if anyone elses truck is like this.

[Ira]

Well, they are not supposed to be that far out. As I recall 25 is the wall. If your MAF is really dirty and reading low you might see that or an air leak might also cause it. I think +25 means the ECM is adding fuel and so you need to look for something that is causing the engine to run lean.

Unless I'm wrong, and in that case I hope someone who knows better will correct me.

Ira

[smslyguy]

here is a run after i cleaned the M.A.F sensor still hitting the +25 long trim fuel. It was running +25 on the stock tune as well there was no changed to the long fuel trims after i made these mods- With this tune i did bump up the timing 2 degrees and put the afr comand to 15.51

[Aloicious]

here is a run after i cleaned the M.A.F sensor still hitting the +25 long trim fuel. It was running +25 on the stock tune as well there was no changed to the long fuel trims after i made these mods- With this tune i did bump up the timing 2 degrees and put the afr comand to 15.51

why are you commanding 15.51 AFR? thats lean and will cause the O2's to add fuel like you're experiencing, try commanding 14.68 and it should help out, that is the only area that the O2 sensors are accurate at, if you're wanting to command anything other than that, you need to run open loop and monitor your fueling with a wideband.

[smslyguy]

why are you commanding 15.51 AFR? thats lean and will cause the O2's to add fuel like you're experiencing, try commanding 14.68 and it should help out, that is the only area that the O2 sensors are accurate at, if you're wanting to command anything other than that, you need to run open loop and monitor your fueling with a wideband.



Even with the stock tune i am experiencing +25 long fuel trims. I am running lean to help with fuel economy which has improved almost 4 mpg.