Tuning MAF for leaner idle for large cam
05-15-2007, 10:15 PM
#1
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Join Date: Feb 2000
Location: Toronto, Ontario, Canada
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Tuning MAF for leaner idle for large cam
As many of you with large Cams...I've bene struggling with a rich idle. I've tried BLM Locker... I've tried adjusting BLM and Integrator Boundaries... I've been able to knock down the fuel at Idle in open loop... but it looks like regardless of what I do... the Fuel at Idle stays about the same...RICH.
I read the following info wjen searching this Computer Section and I learned something new.
I got this from http://para.noid.org/~lj/PCM%20Tutorial/PCMtutorial.htm
I didn't realize that Cell 16 was used only at Idle and was "hardwired" to hit the 14.7 AFR... so no tinkering with AFR at Idle would affect this.
Here is my thought to eliminate the rich problem then.
I've adjusted my MAF tables so that all my BLMs during cruising are in the mid 120's. I've done this so I can limit my BLM's to 129 and integrator values to 150 and was trying to limit the fuel at idle. I still get some values at 129 but usually at lower speeds... closer to Idle.
What I was thinking though, was to lower the BLMS a little more... and not allow BLM's or integrator values above 128. This would prevent the computer from adding fuel anywhere, and can only remove it. This would be done by slightly increasing the MAF table values more than I've already done.
At idle, I would then decrease the values in the MAF table correlating JUST to the airflow Hz that I logged with Datamaster for Idle air speeds.
Since the computer will not be able to add any fuel and Cell 16 is used without any additions from any other tables... I was thinking this may reduce the fuel I'm burning at Idle.
I'll have to try it out this next weekend when the car is out.
What are you thoughts guys....am I missing something?
I read the following info wjen searching this Computer Section and I learned something new.
Cells 16, 17, and 18 are considered to be closed loop cells because they do not use the open loop AFR table. But my understanding is that "learning" is turned off in these cells, which means that the BLMs for these three cells won't be adjusted, even if the O2 sensor feedback indicates that the mixture is not as good as it could be. This means that the term "closed loop" is not an accurate description of what's going on, but we use it to remind ourselves that the PCM is using a fixed value of 14.7 instead of the AFR table. Also, PCM scanners will report that the PCM is in closed loop.
Based on looking at tons of logged PCM data, it appears that cell 16 is used only while the engine is idling (0% TPS and idle RPM), cell 17 is used during engine braking (0% TPS and any RPM [?] above idle), and 18 can be used at any MAP and RPM as long as the TPS is not 0%.
Based on looking at tons of logged PCM data, it appears that cell 16 is used only while the engine is idling (0% TPS and idle RPM), cell 17 is used during engine braking (0% TPS and any RPM [?] above idle), and 18 can be used at any MAP and RPM as long as the TPS is not 0%.
I didn't realize that Cell 16 was used only at Idle and was "hardwired" to hit the 14.7 AFR... so no tinkering with AFR at Idle would affect this.
Here is my thought to eliminate the rich problem then.
I've adjusted my MAF tables so that all my BLMs during cruising are in the mid 120's. I've done this so I can limit my BLM's to 129 and integrator values to 150 and was trying to limit the fuel at idle. I still get some values at 129 but usually at lower speeds... closer to Idle.
What I was thinking though, was to lower the BLMS a little more... and not allow BLM's or integrator values above 128. This would prevent the computer from adding fuel anywhere, and can only remove it. This would be done by slightly increasing the MAF table values more than I've already done.
At idle, I would then decrease the values in the MAF table correlating JUST to the airflow Hz that I logged with Datamaster for Idle air speeds.
Since the computer will not be able to add any fuel and Cell 16 is used without any additions from any other tables... I was thinking this may reduce the fuel I'm burning at Idle.
I'll have to try it out this next weekend when the car is out.
What are you thoughts guys....am I missing something?
05-17-2007, 11:47 AM
#2
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Join Date: Nov 2004
Location: Waterloo, Ontario
Posts: 599
I gave you the answer in your other post weeks ago. Go back and read it from there http://web.camaross.com/forums/showthread.php?t=516088
05-19-2007, 10:01 PM
#3
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Join Date: Nov 2001
Location: Kansas
Posts: 3,517
http://web.camaross.com/forums/showthread.php?t=322365
There is everything you need to know about pulling fuel at idle.
There is everything you need to know about pulling fuel at idle.
05-21-2007, 05:30 AM
#4
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Join Date: Aug 2000
Location: North Vancouver, BC
Posts: 4,305
Did this like 3 years ago, posted it aswell I believe just keep searching, those posts above are good, I haven't driven my car in 2 years, but when I did about 3 years ago I limited my integrators and adjusted maf tables at idle to max out at those limits (integrators) car ran like a champ.
05-21-2007, 07:47 AM
#5
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Join Date: Apr 2005
Location: Florence, Kentucky
Posts: 1,546
I didn't have to mess with the MAF Tables. I just limited the long terms to 0 then I limited the the short terms to +-5. No learning will occur at these settings but the car will still be in closed loop. My car idles at 15.0-17.0 AFR and holds a perfect 14.7 when driving. I did this with Tunercat for OBD2.
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