Startup Adjustments FN1861 - Mechanical Idle
Posted: 2023 May 18, 11:47
I'm working on getting my mechanical idle control sorted out.
What I'm dealing with is startup issues.
I set everything up per the idle air instructions.
Warm idle seems fairly close, maybe a small tweak needed.
Startup is where I'm having issues.
When I start my car in the morning (~60F), the car starts, revs up and then either dies or just barely stays running.
What I noticed is that my ISC duty cycle acts a little odd.
Cranking = 98% duty cycle.
Once car fires and is out of cranking, ISC drops to 17.5% DC and my IPSIBR starts to ramp up (pulling ISC DC up with it).
IPSIBR maxes out at about 0.4 and ISC DC is around 45% and the car runs a bit better as that happens.
RPM is still below DESRPM, but at least the car idles.
Warm start, IPSIBR ramps up to about 0.15-0.2 (somewhere in there) during first few seconds after start and slowly comes back down to 0 after settling in.
What I'm trying to figure out is how much I should be changing FN1861.
I multiplied all rows except the top in that table by 1.2 (i.e. +20%) 2 times and it doesn't seem to change much.
Obviously the values in the table are quite low due to the mechanical idle settings (divide table by 6), so adding that 20% only increases the values in the table by less than 0.1 each time.
Currently, my lower rows are all about 0.5 or below for most columns.
Do I need to bump those lower rows up by a lot more than 20%?
Is there a calculation to determine what values to enter into the FN1861 table based on IPSIBR?
Maybe that's in the idle air or cold start/enrichment writeups, but I didn't see it.
What I'm dealing with is startup issues.
I set everything up per the idle air instructions.
Warm idle seems fairly close, maybe a small tweak needed.
Startup is where I'm having issues.
When I start my car in the morning (~60F), the car starts, revs up and then either dies or just barely stays running.
What I noticed is that my ISC duty cycle acts a little odd.
Cranking = 98% duty cycle.
Once car fires and is out of cranking, ISC drops to 17.5% DC and my IPSIBR starts to ramp up (pulling ISC DC up with it).
IPSIBR maxes out at about 0.4 and ISC DC is around 45% and the car runs a bit better as that happens.
RPM is still below DESRPM, but at least the car idles.
Warm start, IPSIBR ramps up to about 0.15-0.2 (somewhere in there) during first few seconds after start and slowly comes back down to 0 after settling in.
What I'm trying to figure out is how much I should be changing FN1861.
I multiplied all rows except the top in that table by 1.2 (i.e. +20%) 2 times and it doesn't seem to change much.
Obviously the values in the table are quite low due to the mechanical idle settings (divide table by 6), so adding that 20% only increases the values in the table by less than 0.1 each time.
Currently, my lower rows are all about 0.5 or below for most columns.
Do I need to bump those lower rows up by a lot more than 20%?
Is there a calculation to determine what values to enter into the FN1861 table based on IPSIBR?
Maybe that's in the idle air or cold start/enrichment writeups, but I didn't see it.