+25% fuel correction at idle- why?
03-07-2005, 08:09 PM
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+25% fuel correction at idle- why? I've just joined here officially so I can post, as I've been a watcher for quite a while. I enjoyed learning a WHOLE bunch of good tuning tips from you guys and I'm not one to ask a question unless I'm completely without an answer... I've also searched all over for the answer to this as well, but came up with nothing conclusive that I already have not done or tried.
I have a 2002 M6 Camaro H/C car with a pretty big cam, long-tube Hooker headers, Borla exhaust, etc, 427 RWHP. I've done all my own programming and mechanical work to date with very good success and the tune is almost spot-on everywhere in the RPM band, (approx. -2% to -4%) but I have a problem I can't seem to find the solution to..
When I come to a stoplight, I can see the the fueling slowly climb and change from -2% on both sides to eventually pegging it at +25% correction. The VE tables are correct, the MAF has been adjusted slightly in the 3000 Hz range on down to try and compensate, etc, but no matter what I do or try, this thing will NOT change it's attitude...
What am I doing wrong? Are the O2 sensors cooling down too much at idle causing the erratic behavior? Is the cam overlap causing reversion? If so, how does one put this thing into open loop at idle to compensate?
I know this seems like a lot of questions, but I'm pulling my hair out and could really use some advice...
franklin
I have a 2002 M6 Camaro H/C car with a pretty big cam, long-tube Hooker headers, Borla exhaust, etc, 427 RWHP. I've done all my own programming and mechanical work to date with very good success and the tune is almost spot-on everywhere in the RPM band, (approx. -2% to -4%) but I have a problem I can't seem to find the solution to..
When I come to a stoplight, I can see the the fueling slowly climb and change from -2% on both sides to eventually pegging it at +25% correction. The VE tables are correct, the MAF has been adjusted slightly in the 3000 Hz range on down to try and compensate, etc, but no matter what I do or try, this thing will NOT change it's attitude...
What am I doing wrong? Are the O2 sensors cooling down too much at idle causing the erratic behavior? Is the cam overlap causing reversion? If so, how does one put this thing into open loop at idle to compensate?
I know this seems like a lot of questions, but I'm pulling my hair out and could really use some advice...
franklin
03-07-2005, 08:36 PM
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I believe it's the O2s slowly going to sleep; zero output
looks the same as "too lean" as car as the PCM can tell.
Header wrap or higher heater wattage O2s ('vette rears)
address the physical / thermal side, better than programming
can deal with the effects.
looks the same as "too lean" as car as the PCM can tell.
Header wrap or higher heater wattage O2s ('vette rears)
address the physical / thermal side, better than programming
can deal with the effects.
03-07-2005, 10:04 PM
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It's the creeping that makes me think O2s. Easy
enough to view the waveforms on the scanner and
see whether it starts out happy and just loses it.
The other aspects, reversion or leak, are constants.
enough to view the waveforms on the scanner and
see whether it starts out happy and just loses it.
The other aspects, reversion or leak, are constants.
03-07-2005, 10:17 PM
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The camshaft specs are 234/236 @ .050" .601"/.604 114 LSA 112 I.C.L.
Thanks for the info guys and your suggestions have cemented my intial thoughts on why the engine is doing this.
My guess is that the combination of exhaust reversion and the o2 sensors cooling off is really aggravating the issue.
Is there any way I can put this thing into open loop at 1000 RPM and under so that the PCM ignores the lazy, cooling-off O2 sensors? I tried zero'ing out the MAF tables at 3000 Hz on down to see if I could force it into O.L. that way, but all I got was stumbling, rough running, etc, even after I cleaned up the VE tables....
The engine is indeed sealed up tight and runs very well in all other areas of operation, other than extended idle periods.
I wonder if I change header types that don't have the 02's so far from the engine if that will help? Thoughts?
franklin
Thanks for the info guys and your suggestions have cemented my intial thoughts on why the engine is doing this.
My guess is that the combination of exhaust reversion and the o2 sensors cooling off is really aggravating the issue.Is there any way I can put this thing into open loop at 1000 RPM and under so that the PCM ignores the lazy, cooling-off O2 sensors? I tried zero'ing out the MAF tables at 3000 Hz on down to see if I could force it into O.L. that way, but all I got was stumbling, rough running, etc, even after I cleaned up the VE tables....
The engine is indeed sealed up tight and runs very well in all other areas of operation, other than extended idle periods.
I wonder if I change header types that don't have the 02's so far from the engine if that will help? Thoughts?
franklin
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03-08-2005, 08:10 AM
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Thanks smoking, I'll give that a try and since the Vette rear o2 sensors have very long leads, I'll bet I can do away with my current front o2 wiring harness extensions...bonus! 
03-08-2005, 10:47 AM
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Originally Posted by fyi
Thanks smoking, I'll give that a try and since the Vette rear o2 sensors have very long leads, I'll bet I can do away with my current front o2 wiring harness extensions...bonus!
03-08-2005, 11:35 AM
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Originally Posted by fyi
Is there any way I can put this thing into open loop at 1000 RPM and under so that the PCM ignores the lazy, cooling-off O2 sensors? I tried zero'ing out the MAF tables at 3000 Hz on down to see if I could force it into O.L. that way, but all I got was stumbling, rough running, etc, even after I cleaned up the VE tables....
franklin
franklin
03-08-2005, 11:50 AM
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Thanx texhrns, that idea does make sense.. I'll give that a whirl if the Vette o2 sensors don't cure this thing. I've dealt with Motec and BS3 E.M.S.'s in the past and NONE of them had any of this type of bs involved with them...sheesh.
I guess that's what we get using a E.M.S. such as the O.E. stuff when they were designed around emission compliance first- power output second... Oh well..thanx again fellas and carry on!!
I guess that's what we get using a E.M.S. such as the O.E. stuff when they were designed around emission compliance first- power output second... Oh well..thanx again fellas and carry on!!
03-09-2005, 10:29 AM
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The overlap of the cam will let part of the intake charge air(oxygen rich) into the exhaust if a large enough cam is idled low enough. The fresh air entering your exhaust raises the oxygen level. As a result your O2 will report leaner than the actual a/f. This results in the PCM commanding more fuel to be added to bring the A/F back inline(eg +25% ltrims).
DEE
DEE
03-09-2005, 06:11 PM
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Originally Posted by DEE99TA
The overlap of the cam will let part of the intake charge air(oxygen rich) into the exhaust if a large enough cam is idled low enough. The fresh air entering your exhaust raises the oxygen level. As a result your O2 will report leaner than the actual a/f. This results in the PCM commanding more fuel to be added to bring the A/F back inline(eg +25% ltrims).
DEE
DEE
03-09-2005, 08:13 PM
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You might be able to fight this to some extent by making
a screwy O2 threshold vs airflow mode table, down in the
idle range put the O2 voltage very low (though not so low
that the O2 can't swing under). You may want to remap
the mode bins if you are moving more air at idle, than the
highest one in the mode vs airflow table.
I messed with this trying for a poor man's lean cruise, did
not see anything much out of that but not to say it couldn't
work here; seems more like what it was intended for.
a screwy O2 threshold vs airflow mode table, down in the
idle range put the O2 voltage very low (though not so low
that the O2 can't swing under). You may want to remap
the mode bins if you are moving more air at idle, than the
highest one in the mode vs airflow table.
I messed with this trying for a poor man's lean cruise, did
not see anything much out of that but not to say it couldn't
work here; seems more like what it was intended for.
03-11-2005, 09:34 PM
#16
Originally Posted by jimmyblue
You might be able to fight this to some extent by making
a screwy O2 threshold vs airflow mode table, down in the
idle range put the O2 voltage very low (though not so low
that the O2 can't swing under). You may want to remap
the mode bins if you are moving more air at idle, than the
highest one in the mode vs airflow table.
I messed with this trying for a poor man's lean cruise, did
not see anything much out of that but not to say it couldn't
work here; seems more like what it was intended for.
a screwy O2 threshold vs airflow mode table, down in the
idle range put the O2 voltage very low (though not so low
that the O2 can't swing under). You may want to remap
the mode bins if you are moving more air at idle, than the
highest one in the mode vs airflow table.
I messed with this trying for a poor man's lean cruise, did
not see anything much out of that but not to say it couldn't
work here; seems more like what it was intended for.
part throttle operation. Wide band says I'm at 13.7 instead of 14.7.
Just wondered where to find the tables you are calling out. I have LS1edit and have never seen them in there.
Last edited by Cal; 03-11-2005 at 11:22 PM.
