Thread: Help with fuel trims

Originally Posted by 00gpgtp

i get what your saying about the fueling being calculated from the maf when your at wot but why would it pull more fuel when its leaning it out already? so your saying that if its -16 right before pe mode, it will take it to -32 when it enters pe? or did you mean it would add it to make it 0 (in a perfect world). i know a maf tune should be done with the stage 2 tb since that hump is taken out but what about tuning for the stage 1? also, i heard zzp isnt good for a ve tune, true? what is ve mode anyway lol?

first off.
your car wants to run a base afr of 14.7 during normal driving.
in pe mode or wot its 12.4 afr. or what ever zzp set it to.

+16 ltft means your to lean
-16 ltft means your to rich. and the pcm is pulling 16% to get you back to 14.7 afr.

now when the car enters pe mode which is wot. it stops making adjustments to the afr via the o2 sensor and goes on whats stored on the maf tables.

the last fuel trim you hit before you go wot is the fuel trim the pcm will use to adjust your afr in pe mode. so if -16% is the last fuel trim u hit before you go wot (pe mode) the pcm will take that percentage away from your pe's base afr. of 12.4

-16% ltft in pe mode with a base afr of 12.4 would be
(12.4/100*16=1.98+12.4=14.38) 14.38 afr which is lean and would cause kock to show up!

even with a stage 1 tb your fuel trims will be off, some say it wont be that much compared to a stage 2 , but if you can tune for it then do it.
if zzp did a dyno tune i would say it would be good but who knows??

ve mode is just another set of tables to calculate air flow if the maf fails.
some people say tunning in ve mode helps the car out others say its a waste of time because the car isnt using the tables. im not sure on the whole thing.

sorry for the lecture!