PFI Open Loop Idle
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PFI Open Loop Idle
Hey guy's need some suggestions having a hard time with this . I have set the commanded Afr to use the open loop table at idle and some weird things are happening . For those who want to look at what is happening i attached a small data log in DataMaster . To me it looks like the closed loop and open loop are fighting each other just can't pin point the issue . The biggest issue is in decel the Afr goes to 20 near idle then jumps around . 
Re: PFI Open Loop Idle
A/F on a deacceleration at zero TPS/20 MAP it is not uncommon to see that lean A/F as the VAC is very high and shears all the available fuel off the intake tract. As long as the engine does not die(stall saver should prevent) and it may at times you should be OK. What is the commanded A/F set for in OL? I run 13.0/13.3 at idle.
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Car: 1995 Chevy 4x4
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Axle/Gears: 3.73 Limited Slip
Re: PFI Open Loop Idle
My commanded AFR is 16.0 at idle , the only thing is it is not commanding that AFR ? The wide ban is reflecting 14.7 an is very spiky at times , did you look at the data you can see how it spikes very random i think . Here is what i have changed , the open loop AFR parameters stoichiometric AFR is 14.7 maybe that is my problem why it always go back ?
Last edited by 95 4x4; Oct 26, 2009 at 08:23 PM. Reason: added chart
Re: PFI Open Loop Idle
As far as the WB I will say 14.7 is "stoich" for any gas whether it be normal gas or E10. that is true unless you have the WB calibrated for E10 assuming you are running E10 as I am. If you were to flip the WB to read Lambda .90-1.10 where 1.00 is stoich it would then read 1.00 as stoich regardless of fuel. Now you say "spikes". there is a function to aveage the changes in A/F that occur radidly in the WB controller. In fact my pillar DB gauge does not show the A/F activity that the contrroller does. It smoothens more so. I idle 13.0-13.3 and it moves around there and updates once a sec. In CL the NB is moving the A/F constantly over stoich or .45 mvolt. You can tighen up those swings if you like as I did in rich/median/lean as well. I chose to idle OL but no emishions for me.
Why are you commanding 16.0/1 emmishions? I would set to 14.3 and try that. I understand the commanded idle A/F is what it will target. L/R/M I think is the swing amounts.
I dont know how to read that file.
Why are you commanding 16.0/1 emmishions? I would set to 14.3 and try that. I understand the commanded idle A/F is what it will target. L/R/M I think is the swing amounts.
I dont know how to read that file.
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Re: PFI Open Loop Idle
Been doing alot of experimenting with the idle and come to the conclusion , their is something causing no command of A/F at idle in OL . While in OL full time no problem at all with the AFR only when commaned OL @ idle . I can see that the AFR using battery volts increase from 12.0 to 14.7 AFR and it will never go further stops dead at 14.7 using the WB to verify .
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Re: PFI Open Loop Idle
Is this a TBI PCM being used for the PFI? If so, you will need to disable closed loop entirely to get it to idle at AFRs other than stoich. The PCMs will still allow you to run AFRs other than stoich, but most of the closed loop logic is still in effect.
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Axle/Gears: 3.73 Limited Slip
Re: PFI Open Loop Idle
Yes this is a TBI PCM used for PFI . I don't no how these other members are getting thiers to idle in open loop but i can't using their configuration at least to achieve the afr i was hoping for ? I was also gonna look into this open loop parameter ( open loop idle lean limit vs temperature ) . When i follow my data for idle it seems to minic this table afr wise anyway and maybe this is what is causing my limit to alter my afr at idle . I would prefer to alter my 02 at idle for a different afr because i thought it was easier but not . I never even had a hint of luck with that one no matter how much i read and tried so i figured open loop at idle was the way to go at this time .
Last edited by 95 4x4; Nov 29, 2009 at 10:07 AM. Reason: after thought on afr
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Re: PFI Open Loop Idle
Actually, it does allow open loop idle, to an extent. What I said above applies only to the main AFR vs. cool temp table. I went back and took a look at how it works. Here are the parameters that control the open loop idle:
there are some strings attached to the open loop idle. If you do not have AIR, the PCM will not allow open loop idle in park/neutral. It will remain in closed loop. The open loop idle is only allowed in drive in that case. The open loop idle AFR is calculated from the table you have shown along with the bias that is used at cooler temps. The bias at L48DE is subtracted out at cooler engine temps to enrich the AFRs. There is also a time that determines how long to wait before switching from the stoich AFR to the open loop idle AFRs.
Code:
;
;~~~~~~~~~~~~~~~~~~~~~~
;-Open loop idle quals
;~~~~~~~~~~~~~~~~~~~~~~
;
L48D4 FCB 255 ;255 sec, timer threshold to enable open loop idle
L48D5 FCB 0 ;0 secs, timer threshold to transition to open loop idle AFR
L48D6 FDB 0015 ;15 sec, time after startup to clear initial idle terms
L48D8 FCB 100 ;35 dec C, threshold to remain in open loop idle
;
;~~~~~~~~~~~~~~~~~~~~~~
;-Open loop AFR params
;~~~~~~~~~~~~~~~~~~~~~~
;
L48D9 FCB 173 ;90 deg C, temp threshold for open loop idle AFR bias
L48DA FCB 0 ;-40 deg C, lower cool temp for open loop AFR enrichment
L48DB FCB 254 ;151 dec C, upper cool temp for open loop AFR enrichment
;
L48DC FCB 200 ;10 secs, time limit for initial AFR enrichment
;
L48DD FCB 147 ;14.7:1, stoich AFR
;
L48DE FCB 16 ;1.6:1 AFR bias for open loop idle
; Used prior to TPS action after start up
;
L48DF FCB 147 ;14.7:1 AFR, lower limit for quasi-closed loop
L48E0 FCB 10 ;1.0:1, initial AFR enrichemnt
L48E1 FCB 5 ;0.5:1, initial AFR enrichment if in park/neutral
L48E2 FCB 6 ;Filter coeff. for filtering AFR after transition from idle Last edited by dimented24x7; Dec 1, 2009 at 03:24 AM.
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Axle/Gears: 3.73 Limited Slip
Re: PFI Open Loop Idle
Thanks for the info explains alot with the trouble i'am having . I do not have Air and from what you just said now wonder when i was in drive and in park it was acting weird . Let me ask you this by doing a few plug reading's at idle the WB read a 15.5 AFR and that gave me a light tan colour and idled very nice . All i'am trying to do is stop the PCM from dumping in the fuel at idle due to my cam overlap and changing my idle 02 thresholds had no impact at all .
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Re: PFI Open Loop Idle
At idle you will need to read the plugs. The cam overlap will render the WB O2 readings meaningless. Also, the overlap will cause the O2 readings to zero out. I know my O2s only read about 20-30 mV at idle, so no ammount of bias will correct for that.
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From: Windsor , Ontario
Car: 1995 Chevy 4x4
Engine: 355 cu. in. Vortec / TPI / MAF
Transmission: 4L60E
Axle/Gears: 3.73 Limited Slip
Re: PFI Open Loop Idle
I have the reading's for the plugs at idle in open loop an saved them for one day i can figure out how to use them . Yes i agree the WB at idle is meaningless . I have increased my idle thresholds higher then stock an they seem not to make a difference at all . Here are the tables i have adjusted maybe i'am going the wrong way if not how much higher can i go ?
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