Strange LTFT problem causing stumbling, hesitation
Thread Starter
Staging Lane
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Joined: May 2006
Posts: 70
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From: Lisbon Falls, Maine!
Strange LTFT problem causing stumbling, hesitation Okay, this has been going on for a while now and I am reaching my wits end with it. I have been told that it was most likely an exaust leak just downstream of the O2 that was pulling fresh air across the O2 on decel while the engine is under vaccum, but I just installed some new headers and I KNOW there are NO exhaust leaks at all. When I am driving along, if I allow the car to decel in gear, if I try to get back on the gas quickly, the car stumbles momentarily and then takes off like a bat out of hell. I have included a couple of links to some scans I did today, headers.efi is a shorter log than headers 2 but they were made back-to-back. You will notice that at times, my LTFT's are up to 10% different. The problem is obviously on Bank2, but I have seen the same issue happen on Bank 1 at times. Any ideas?
http://www.nlcphoto.com/logs/headers.efi
http://www.nlcphoto.com/logs/headers2.efi
Thanks,
Nick
http://www.nlcphoto.com/logs/headers.efi
http://www.nlcphoto.com/logs/headers2.efi
Thanks,
Nick
I've read that if the MAF output drops off the bottom of the table range,
it freaks out some of the older calibrations. Wonder what you see for the
raw frequency at closed throttle decel.
You probably will find more interesting action in the STFTs, see if they
are moving a lot while the car is "catching up" from stumbling. If so you
may have a problem with decel and light acceleration being in the same
fuel trim cell but being nothing alike, maybe a VE table which doesn't
cover the MAP dimension very accurately. Not too many people try to
tune deceleration and it may "taint" the fuel trims for a bit after.
Make sure you have decel putting you in a different fuel trim cell
than your cruise and acceleration closed loop.
If you have an active deceleration fuel cut, and push very little
exhaust, your O2s may be pretty sleepy and push trims on that
basis (false trimming).
it freaks out some of the older calibrations. Wonder what you see for the
raw frequency at closed throttle decel.
You probably will find more interesting action in the STFTs, see if they
are moving a lot while the car is "catching up" from stumbling. If so you
may have a problem with decel and light acceleration being in the same
fuel trim cell but being nothing alike, maybe a VE table which doesn't
cover the MAP dimension very accurately. Not too many people try to
tune deceleration and it may "taint" the fuel trims for a bit after.
Make sure you have decel putting you in a different fuel trim cell
than your cruise and acceleration closed loop.
If you have an active deceleration fuel cut, and push very little
exhaust, your O2s may be pretty sleepy and push trims on that
basis (false trimming).
