Commanding 15.12 AFR but not getting it in closed-loop
12-09-2005, 03:26 PM
#1
Commanding 15.12 AFR but not getting it in closed-loop All I changed was the "Air Fuel Ratio, Stoich AFR" field (to 15.12). Scanned and saw my commanded-AFR was correct (15.12) but my WB still reports 14.62 (approx.), which is what I was getting before the change. Sooo.. I changed it even more, to 15.62 and logged. Still getting the same WB results of 14.62 (approx.).
Is there another field/setting I need to adjust in order to change my closed-loop AFR??? OR Do I have to re-do my SD-VE tuning and MAF calibration for this new closed-loop AFR?
Is there another field/setting I need to adjust in order to change my closed-loop AFR??? OR Do I have to re-do my SD-VE tuning and MAF calibration for this new closed-loop AFR?
12-09-2005, 04:36 PM
#2
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I think the only feedback the PCM has, for closed loop,
is the cross-counts. And if you tell it stoich is 15.12345
it's going to believe that the crossing point is still the
sign that it hit it. Open loop you should see a change
in fueling but closed loop it's going to go right back to
50% average time above and below.
is the cross-counts. And if you tell it stoich is 15.12345
it's going to believe that the crossing point is still the
sign that it hit it. Open loop you should see a change
in fueling but closed loop it's going to go right back to
50% average time above and below.
12-10-2005, 12:07 PM
#4
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I believe o2s are 'tuned' for lambda, which is ~14.63 for gasoline engines. I've never really seen anything that can alter closed-loop afr, unless maybe you change to different o2s. I'm curious as to whether anyone has some thoughts on this?
12-10-2005, 03:51 PM
#5
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Check out B4105 in efilive from previous discussions I understand you can alter the "switch points" basically the voltage at which the sensors switch from lean to rich (stoich), this might help you to reset your O2's to command the "correct" closed loop value.
Generally as noted closed loop will command stoich 14.63:1 try messing with the switch points and monitor WB02 and see what happens.
Generally as noted closed loop will command stoich 14.63:1 try messing with the switch points and monitor WB02 and see what happens.
12-10-2005, 07:31 PM
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When should you use the VCM Controls AFR Control, and how would should you use it properly? This is in the Hptuners Scanner.
Last edited by alchemistz06; 12-10-2005 at 07:32 PM. Reason: add stuff
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12-10-2005, 08:14 PM
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Under ordinary circumstances, you run in closed loop almost all the time during daily driving. The switching point for the narrow band oxygen sensors is stoichiometric (about 14.68 AFR for gasoline). I don't see what role this stoic value field really plays if anything at all whether in open loop, closed loop, power or cold start enrichment, or anything else. It seems like to me that the developers of the PCM at GM Powertrain envisioned a role for this parameter initially, but in time, they never really used it.
Steve
Steve
12-10-2005, 09:59 PM
#9
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What you are trying to do will not work with the narrow band O2's by the nature of their design.
You can achieve your goal by tuning and running in open loop which doesn't use the O2's at all. It's a bit of work since you do your tuning in the VE table.
You can achieve your goal by tuning and running in open loop which doesn't use the O2's at all. It's a bit of work since you do your tuning in the VE table.
12-11-2005, 09:43 AM
#11
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Stoich target value is used in all forward fuel shot
calculations, it's the prime scale factor. But in the
feedback system the result will be corrected out.
In closed loop all you can do is lower the switch
threshold (O2 voltage vs airflow mode) enough
that you get some increase in AFR target by the
slope of the O2 transfer function. But this is a
pretty steep curve and not a whole lot to gain
until you get pretty low, perhaps marginal in some
other way. But if you went and, say, put these
thresholds in your cruise airflow mode area to
250mV and rechecked your AFR average in closed
loop, you should see some deflection toward the
lean.
In my opinion the Stoich value ought to be left (or
put, if you're dealing with oxygenated fuel or an
alcohol blend, which is oxygenated too) to the true
chemical number.
calculations, it's the prime scale factor. But in the
feedback system the result will be corrected out.
In closed loop all you can do is lower the switch
threshold (O2 voltage vs airflow mode) enough
that you get some increase in AFR target by the
slope of the O2 transfer function. But this is a
pretty steep curve and not a whole lot to gain
until you get pretty low, perhaps marginal in some
other way. But if you went and, say, put these
thresholds in your cruise airflow mode area to
250mV and rechecked your AFR average in closed
loop, you should see some deflection toward the
lean.
In my opinion the Stoich value ought to be left (or
put, if you're dealing with oxygenated fuel or an
alcohol blend, which is oxygenated too) to the true
chemical number.
12-11-2005, 04:44 PM
#13
The maf doesn't care what your A/F ratio is. The O2's do. You can run open loop with a Maf and run whatever A/F ratio you want. As soon as you go closed loop though it will try to go 14.7.
