I've seen so many posts lately about people saying they're running rich, but I'm confused. I was under the impression that if your LTtrims are say -10% in a few cells doesn't that just mean the computer is subtracting fuel and if the computer wasn't subtracting fuel your car would be running rich? I thought that was the whole point of the LTtrims and STtrims, to compensate for a rich/lean condition so that the computer corrects to the right A/F ratio.

Also, if your LTtrims are negative and you go WOT, won't it just use 0 as the values in the cell? If so, why does it matter if you're -5% or -10%?

 

you are correct...

in closed loop you cannot run rich/lean unless you have a severe condition where the PCM isnt able to correct due to BLM boundaries of 160 and 108.

you can still run rich/lean in open loop and WOT you can typically only run rich. if say you have a fuel trim(BLM) of 115 then it will default to 128 or if you have OBD2 then it would be 0%.

 

Thanks for the reply. That brings me to my next question. Lets say in all the cells your values stay right around 0% or go into the negatives, what's the point in using something like an MAF translator or custom tuning to bring the values as close to 0 as possible?

 

when the values are in the negatives or under 128 then when you go to WOT, the PCM will calculate the target AFR as usual but with a multipication factor of (fuel trim under 128)/128. so if you are close to 128 then there really wont be that big of a change in your AFR but if you are say at 110 then a target AFR of say 13.5 will be adjusted to 13.5*(110/128)=11.6 which will hurt power considerably.

what a MAF translator does is manipulate the MAF frequencies and trick the PCM into thinking you are getting more/less air than is actually entering the motor. since the computer adjusts any changes you make, the MAF translator is basically another gimmic. now if you are -10% or 115 blm then adjusting it could raise the fuel trims to near 0% or 128 giving you a better AFR at WOT and therefore increasing power. if you have LT1 edit or tunercat, you can adjust the MAF tables in the PCM to get the same results but just takes a while longer since you must reflash teh computer everytime you change the table for your changes to take affect.

 

Does it just use the values of which ever cell you're in right before you go WOT?

One reason I've been asking all these questions is because in one cell my LTtrims drop as low as -13% on one side and -5% on the other, but this is only at idle or when I'm decellerating. All my other cells are not split by much, if any, and are typically between 0 and -6%. I just wanted to know if this is a problem or I should just not worry about it.

 

it uses the cell before WOT.