Decel after closed loop, AFR gets too FAT
Decel after closed loop, AFR gets too FAT Swapped out the OEM 26# injectors for 42# injectors and updated the IFR table. Now I get a drop in AFR every time I release the throttle.
In otherwords, every time I'm in closed loop the AFR drops from 14.7 to ~11 or 12 when the throttle closes. Afterwhich, the PCM/O2's take a few moments to hunt for proper AFR.
I reviewed old logs from before the injector swap and noticed that AFR was dropping to ~13 on decel. However, it never bothered my because the feedback returned to 14.7 quickly.
Hopfully someone could recommend how to tackle this. In gear during decel (including slight throttle decrease or throttle postion 0%) does fuel rely on VE table or MAF? If VE, does it make more sense to adjust IFR or VE to thin out the fuel? What is the ideal AFR during decel while in closed loop? 14.7?
Note: I did notice a slight decrease in LTFT after the injector swap and IFR update.
In otherwords, every time I'm in closed loop the AFR drops from 14.7 to ~11 or 12 when the throttle closes. Afterwhich, the PCM/O2's take a few moments to hunt for proper AFR.
I reviewed old logs from before the injector swap and noticed that AFR was dropping to ~13 on decel. However, it never bothered my because the feedback returned to 14.7 quickly.
Hopfully someone could recommend how to tackle this. In gear during decel (including slight throttle decrease or throttle postion 0%) does fuel rely on VE table or MAF? If VE, does it make more sense to adjust IFR or VE to thin out the fuel? What is the ideal AFR during decel while in closed loop? 14.7?
Note: I did notice a slight decrease in LTFT after the injector swap and IFR update.
First, check the logged injector pulse width against the
sum of injector offset (volts, pressure) and min injector
pulse width (tune file). Stepping up that much in injector
size may just mean that the minimum delivered pulse is
more than decel airflow can burn straight-up.
sum of injector offset (volts, pressure) and min injector
pulse width (tune file). Stepping up that much in injector
size may just mean that the minimum delivered pulse is
more than decel airflow can burn straight-up.
I'd just back into it, keeping an eye for any issues like
roughness / uneven behavior at low pulse widths. I do
not know why there is a minimum floor value other than
perhaps thoroughness, avoiding divide-by-zero or some
deal like that.
It's also possible that the very low airflow VE / MAF is
just not right, but specifically checking the injector pulse
vs limits will narrow the list of suspects.
Seems more than a few folks have had what look like
injector offset value problems with 42#ers too, not to
mention there are at least two different species of 42#
in common use (SVO, Delphi/Lucas) with presumably
different dynamic characteristics. Have yet to see any
good offset numbers though I took a whack at figuring
some, from Web available data (see .gif; they ought to
allow Excel attachments don't you think?). The yellow
calculated offset time (mS) varies widely and the Delphi
42s are much lower (quicker) than most others, another
potential skew affecting very-low-flow operation out of
proportion.
roughness / uneven behavior at low pulse widths. I do
not know why there is a minimum floor value other than
perhaps thoroughness, avoiding divide-by-zero or some
deal like that.
It's also possible that the very low airflow VE / MAF is
just not right, but specifically checking the injector pulse
vs limits will narrow the list of suspects.
Seems more than a few folks have had what look like
injector offset value problems with 42#ers too, not to
mention there are at least two different species of 42#
in common use (SVO, Delphi/Lucas) with presumably
different dynamic characteristics. Have yet to see any
good offset numbers though I took a whack at figuring
some, from Web available data (see .gif; they ought to
allow Excel attachments don't you think?). The yellow
calculated offset time (mS) varies widely and the Delphi
42s are much lower (quicker) than most others, another
potential skew affecting very-low-flow operation out of
proportion.
i had to reduce the offset table in low MAP areas by about 20% and now the car only goes to about 13.4-13.0 on decel, and it was 11:1-12:1 before. i coudl put 0 in for the VE and it would still be rich, the injectors are just not able to flow that low. i have FMS 42#ers as well
