I only recently started to read about fuel trim on the forums. Currently I have AEM intake, Ichiba test pipe, Greddy SE exhaust and Cobb Stage 2 OTS map with pill still in. Is it normal to see at light throttle on the highway on 5th gear between 2.5k-2.9k rpm the STFT starts to spike up and down varying between +7% and -7%? Also during idle the STFT just zig zags up and down between +5% and -5%. The majority of the time during the drive when I'm in a accelerated cruise, throttle, or let off the gas it stays at 0% which is ideal. I haven't looked into the LTFT yet but when I glimpsed at it for a sec during highway crusing I saw mostly 0% flat and some -0.85% spikes. Is the car running fine or is the fuel trim really out of balance as that I saw some numbers higher than 5%.

 

STFT movement is perfectly normal...

infact thats how it maintains floating around stoich for cat efficiency

 

worry about your LTFT idle and cruise being around 0% more than anything.

 

LTFT idle is 0.8% and cruise is 1.3% constant. Not close to the 0% I was looking for but yesterday when the weather was warmer it was 0.3% idle and 0.8% cruise.

 

those are perfect trims. usually people try to get them between +-5%

 

I just looked at my LTFT again today in the morning and in the afternoon after work. In the morning at 40 degree weather it was 0.8% idle and 2.3% cruise and at 65 degree weather it was 0.8% idle and 3.1% cruise. Seems like the higher the temperature the fuel trim is trying to lean out to retain a balance. I Cobb flashed my car in the winter times at 30 degree weather and reset the car by removing the negative from the battery when I worked on my car over the winter. If I reset the car again but leave the cobb tune on will the fuel trim learn to adapt to the new initial temperature and work it's way around that?

 

first off, i think you have the understanding of the fuel trims backwards. when the trims are positive it means that ecu isn't seeing enough fuel so it compensates with that percentage. so in your case, it means that when you reach higher temperatures you car is leaning out so the fuel trims are actually adding fuel to even it out. which doens't make sense because with hotter temperatures your car should be going richer not leaner since the air is not as dense. interesting though.

ps. i honestly wouldn't worry about your trims, they are good.