Please don't simply tell me to search. I had my car tuned for about 6 months now and over the summer my wideband has went from bouncing around 12's under load to now dipping into the 9's. I think this may have started after taking a few long 100 mile drives at a constant speed in high temps. Cruising seems fine but after building boost my AFR goes rich and it's definitely not as quick as it once was. I need to get a scanner, but does this sound like a fuel trim issue or something else going on here? I have disconnected the battery for a day to no avail...shouldn't this reset the trims?

 

anything that is under WOT load or above 4000rpms under load is not related to fuel trims... if u wer eu id be looking for boost leaks... sounds like that what you have

 

That's a great suggestion. I was hoping to avoid doing that again. I'll try to give it a whirl before i go to the track tomorrow...before i got it tuned i had to rtv the turbo housing, maybe it's the same problem. It seems like around 4000 rpm it hits a wall, so it may still be a tuning issue. Does disconnecting the battery reset the trims?

 

if your trims are off you have a problem and disconnecting the battery won't fix the problem. find and fix the problem and the trims will return to normal.

 

no it will not fix the problem. However if it is the trims and i reset them before i go to the track tomorrow my afr will be normal for awhile; then I know i'll need to purchase scanning software and start playing with the tune. So my question still stands....does disconnecting the battery reset the trims?

 

no
fuel trims correct themselves within minutes of starting.
if u do have an issue no matter what u do you ecu will alter the trims

 

must be a boost leak issue...I thought the ltft's took longer than a few minutes to adjust. Thanks for the help

 

any time

 

Okay, I want to clear things up for folks on fuel trims. The fuel system has two primary states, closed loop and open loop. yes there are variations, but for this discussion these are the ones that matter.

So here we go -

Closed loop - when cruising or at low->moderate throttle input at low->mid rpm's the car is in closed loop. During this the stft's are constantly changing due to feedback from the 02 sensor (realtime) and thus slowly changing the ltft's. ltft's change relatively slowly - theres no exact time, however a sudden +15 blip in stft for 2-3 sec will not nessecarilly affect the ltft at all. Now if that large positive (or neg) stft is SUSTAINED for a long period of time, it will affect the ltft. STFT's are real time and do not hold a value. LTFT's are learned over time while driving the car and are stored in the ECU. The total fuel added or removed at any given time is a sum of the LTFT and the STFT.

Now for Open Loop - Youll see this condition when at high throttle and/or above about 4000 rpm. During open loop, the ECU is NOT recieving feedback from the 02 sensor, thus no stft. However, You STILL WILL SEE AN LTFT!! This is calculated while the car is in closed loop, than applied during open loop. So the LTFT's calculated during closed loop WILL affect the AFR during wot/open loop.

To reset the LTFT, simply disconnect the ECU (or battery) for 10 min. No it doesnt really take this long - ive seen it reset in 30sec-1min however this insures that any residual power in the circuit completely drains allowing the ECU to reset.

 

well you say it happened now that its in the summer....what management are you using? perhaps its your IAT map.

 

Thank you for clearing that up thendawg i suspected the ltfts played a part in wot. I am using an FIC and thought iat was the culprit, but it has been quite a bit cooler lately and I still have the problem. Long story short...I modified my full boost fuel trims at the higher rpm levels on my way to the track, and i was getting a fairly close 12 AFR. My clutch apparently didn't like the track at all...so now I should look into getting a new one. Any suggestions?