What AFR under decel?
05-29-2012, 02:13 PM
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What AFR under decel? I'm in the process of dialing in VE on one of my vehicles, and now have it within 2% while tuning in OLSD.
I'm wondering what "normal" AFR should be in the 15kpa-20kpa areas when shooting for a 14.4 AFR under normal driving/cruise conditions. Under decel, the AFRs will swing hard to 10-12. Is this something that I should be trying to tune more to stoich value, or is there a benefit to having it go rich under decel?
Thanks for any help. I'm just trying to get as much information/experience as possible before hitting up the Tuning School seminar in July.
I'm wondering what "normal" AFR should be in the 15kpa-20kpa areas when shooting for a 14.4 AFR under normal driving/cruise conditions. Under decel, the AFRs will swing hard to 10-12. Is this something that I should be trying to tune more to stoich value, or is there a benefit to having it go rich under decel?
Thanks for any help. I'm just trying to get as much information/experience as possible before hitting up the Tuning School seminar in July.
05-29-2012, 06:35 PM
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There's no value to being rich at decel, this may just
be your minimum injector pulse width against the air
you can't stop (PCV, throttle blade hole, etc.). The
PCV air is quite rich unless you've -just- changed
the oil.
Look at the logs for delivered PW on decel, the tune
file for the min PW limit, and see if they just happen
to agree.
DFCO cuts the injectors out on decel and would put
you dead lean instead, for some economy improvement
(but hassles when modded).
This (poor AFR control on decel) means you want one
row of your FTC table to be below your minimum cruise
MAP, so the garbage will have somewhere to fall without
bending your normal-running fuel trims.
be your minimum injector pulse width against the air
you can't stop (PCV, throttle blade hole, etc.). The
PCV air is quite rich unless you've -just- changed
the oil.
Look at the logs for delivered PW on decel, the tune
file for the min PW limit, and see if they just happen
to agree.
DFCO cuts the injectors out on decel and would put
you dead lean instead, for some economy improvement
(but hassles when modded).
This (poor AFR control on decel) means you want one
row of your FTC table to be below your minimum cruise
MAP, so the garbage will have somewhere to fall without
bending your normal-running fuel trims.
05-29-2012, 07:02 PM
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Thanks. Definitely food for thought. I've just been finding it a bit annoying that it dips so much on even slight decel transitions. Maybe I'm just being too picky about it, but it would be nice if it were possible to lessen the effect a bit....maybe gain a little fuel economy. DFCO is disabled, and I have not really messed with it. Still learning and trying not to dig too deep and screw things up. lol
05-30-2012, 01:55 PM
#4
Jimmy's right about DFCO being a pain and how to troubleshoot it. All you can do is set your target AFR real high or VE real low and let it hit the minimum pulse width.
My main annoyances with DFCO are:
The loud pop sound when DFCO initially kicks in. I guess this is from the last bit of fuel burning out the combustion chamber. Kind of sounds like a small back fire.
Then the "18-wheeler on the exhaust brake" sound after it kicks in and engine braking. It slows the car down too quickly when cruising low speed, but nice when coming to a stop.
There is also an abrupt transition when getting back on the throttle.
The reason I leave it on is I think that DFCO keeps the combustion chambers from getting excess fuel and washing the cylinders. I honestly don't know if this is the case or not.
My main annoyances with DFCO are:
The loud pop sound when DFCO initially kicks in. I guess this is from the last bit of fuel burning out the combustion chamber. Kind of sounds like a small back fire.
Then the "18-wheeler on the exhaust brake" sound after it kicks in and engine braking. It slows the car down too quickly when cruising low speed, but nice when coming to a stop.
There is also an abrupt transition when getting back on the throttle.
The reason I leave it on is I think that DFCO keeps the combustion chambers from getting excess fuel and washing the cylinders. I honestly don't know if this is the case or not.
05-30-2012, 02:17 PM
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Jimmy's right about DFCO being a pain and how to troubleshoot it. All you can do is set your target AFR real high or VE real low and let it hit the minimum pulse width.
My main annoyances with DFCO are:
The loud pop sound when DFCO initially kicks in. I guess this is from the last bit of fuel burning out the combustion chamber. Kind of sounds like a small back fire.
Then the "18-wheeler on the exhaust brake" sound after it kicks in and engine braking. It slows the car down too quickly when cruising low speed, but nice when coming to a stop.
There is also an abrupt transition when getting back on the throttle.
The reason I leave it on is I think that DFCO keeps the combustion chambers from getting excess fuel and washing the cylinders. I honestly don't know if this is the case or not.
My main annoyances with DFCO are:
The loud pop sound when DFCO initially kicks in. I guess this is from the last bit of fuel burning out the combustion chamber. Kind of sounds like a small back fire.
Then the "18-wheeler on the exhaust brake" sound after it kicks in and engine braking. It slows the car down too quickly when cruising low speed, but nice when coming to a stop.
There is also an abrupt transition when getting back on the throttle.
The reason I leave it on is I think that DFCO keeps the combustion chambers from getting excess fuel and washing the cylinders. I honestly don't know if this is the case or not.
