Closed Loop Bias question
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Road Master
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Closed Loop Bias question
I have my map perfect with the help of the smart tune. Only one problem, I have my map set to go in to the closed loop mode at 2500 to 3000 rpm in the 20 to 80 kpa, a small window but it works great when cursing down the high way in saving gas. But I would like to richen it up a little. If I increase the closed loop bias for that range what would that lower my afr to in closed loop. now I am ate 14.6 but would like to be at around 14.3 and not lose the o2 sensor feature.
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From: Back in the Good Ole USA. South Carolina to be exact.
I have my map perfect with the help of the smart tune. Only one problem, I have my map set to go in to the closed loop mode at 2500 to 3000 rpm in the 20 to 80 kpa, a small window but it works great when cursing down the high way in saving gas. But I would like to richen it up a little. If I increase the closed loop bias for that range what would that lower my afr to in closed loop. now I am ate 14.6 but would like to be at around 14.3 and not lose the o2 sensor feature.
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Road Master
Joined: Sep 2006
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Yes I thought about getting out of the closed loop function and setting the ve tables to 14.3 but I like the ability to have the ecm adjust the afr especially if you in high altitudes. May be I am being to picky.I was just wondering if some one has played around with the CLB table. Thank’s for the help.
Elite HDF Member
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From: Back in the Good Ole USA. South Carolina to be exact.
Yeah, it's very common to tweak the CLB to retain Closed Loop at a richer AFR. I think the purpose of the CLB is to adjust for the stoichoimetric point of the fuel.
Extreme HDF Member
Joined: Sep 2005
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From: Baton Rouge, LA
Only one problem, I have my map set to go in to the closed loop mode at 2500 to 3000 rpm in the 20 to 80 kpa, a small window but it works great when cursing down the high way in saving gas. But I would like to richen it up a little. If I increase the closed loop bias for that range what would that lower my afr to in closed loop. now I am ate 14.6 but would like to be at around 14.3 and not lose the o2 sensor feature.
If I was in your shoes and had the stock NB sensors installed I would run closed-loop and set CLB to 700 or maybe 750. I'm running 14.5 in the cruise range and find that the engine does not run hot, as shown by ET (FCHT reported by the ECM) and OT, and mileage is near optimized at that AFR. I think there is much exaggeration about the cooling benefits of running richer AFR's, as I've run tests at cruise set to 13.0, 13.8, and as high as 14.6 that shows little difference in either ET and none for OT. See attached chart for the relationship between CLB (mV), Lambda, and AFR.
You can retain closed-loop and adjust CLB, but there is a very narrow range you can work with, up to about 750mv (14.58:1). Setting it to 786 would achieve 14.39:1, which would probably work okay even though it is getting out of the sensors' comfort zone and I suspect sensor accuracy would be compromised at or above that setting.
You can also just run open-loop and as you've already observed you'll likely find that there'll be no measurable difference in performance or mileage. When I do datalogging I rarely see more than ą2% variance anywhere in the RPM/TP range in open-loop, and that's pretty close. CL may get it a bit tighter, but if so I wonder to what practical effect.
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Road Master
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To me it seems like the clb table is to fine tune the closed loop to 14.6. Let’s say that in closed loop your running at 14.3 then you would adjust the clb table to make it 14.6 I could be wrong but that is my guest. Thanks for the chart it is very helpful.
Elite HDF Member
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From: Back in the Good Ole USA. South Carolina to be exact.
The purpose of the CLB is to adjust for the stoichoimetric point of the fuel.
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From: Baton Rouge, LA
That's my understanding too. Once you get VE correct you should be able to change CLB and AFR within the acceptable parameters and expect the ECM to do the math and provide the correct adjustment.