Strange LTFT problem
10-10-2005, 09:07 PM
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Strange LTFT problem This is driving me nuts. 
Leaving the car in park or neutral, both LTFT's run up to 24.9 and I get a 171 and 174 code. If I put the car into drive, reverse or any gear, both LTFTs instantly decline to 16 or 17. This change is instant - did drive/neutral several times and the same thing. There is no change in engine sound or anything else other then the idle decreasing a bit when going from neutral to drive. Any thoughts on this would be greatly appreciated.
Thanks,
Roy
Leaving the car in park or neutral, both LTFT's run up to 24.9 and I get a 171 and 174 code. If I put the car into drive, reverse or any gear, both LTFTs instantly decline to 16 or 17. This change is instant - did drive/neutral several times and the same thing. There is no change in engine sound or anything else other then the idle decreasing a bit when going from neutral to drive. Any thoughts on this would be greatly appreciated.
Thanks,
Roy
10-11-2005, 09:21 AM
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Originally Posted by P Mack
Park and drive use different fuel trim cells, so the instant change is normal. You're ltfts are very high though, have you messed with your ve table before?
Roy
10-11-2005, 09:38 AM
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I believe a stock VE table against that cam would
produce negative trims (VE being degraded at idle,
not represented, making positive airflow calc error
and overfueling). Trims are indicated postive.
My suspicion is that the headers are driving false
trimming, that the drive LTFTs are better because
that trim cell encompasses some higher load, hence
higher exhaust heat, making the quality of trimming
better (not good, just better).
The first thing to do is to look at the idle O2 real
time waveforms and determine whether the O2s are
working well, or just barely hanging on. That's the
basis for all trimming and it wants to be happy.
The codes are just griping that LTFTs are bumping
over +25
produce negative trims (VE being degraded at idle,
not represented, making positive airflow calc error
and overfueling). Trims are indicated postive.
My suspicion is that the headers are driving false
trimming, that the drive LTFTs are better because
that trim cell encompasses some higher load, hence
higher exhaust heat, making the quality of trimming
better (not good, just better).
The first thing to do is to look at the idle O2 real
time waveforms and determine whether the O2s are
working well, or just barely hanging on. That's the
basis for all trimming and it wants to be happy.
The codes are just griping that LTFTs are bumping
over +25
