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Not wanting to jack another thread you responded to, you talked about high cruise afrs in lean cruise with 7427. I have been able to manipulate my afrs to the way I want them but have only been able to do so in open loop. It has been very successful but wondered if you were doing it in closed loop. If so any hints on how to do it?
Not wanting to jack another thread you responded to, you talked about high cruise afrs in lean cruise with 7427.
Me too - don't mean to jack your thread. I'm always curious about everything to do with HLC. When I'm starting to cruise (7747 ECM) it goes into Closed loop and BLM. As soon as it goes into HLC it goes out of CL and BLM. I'm looking at my tables and Closed Loop max lean AFR is set @ 15.5, HLC is higher than that @ lower kPa's and BLM min is too high when running so lean. Can we change CL max lean to get into Closed Loop? Why would we want to go into closed loop? Will that screw up our BLM map? Good questions for someone smarter than me...
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Unless you have some kind of a wideband patched into the ECM code you cannot run closed loop lean cruise. You have to dial in your VE tables then it has to be open loop and commanded air/fuel ratio has to be leaner.Quote:
Originally Posted by myburb
To further explain. A narrow band O2 sensor only works to tell the ECM if the AFR is above or below stoichiometric (the "perfect" AFR). This means that closed loop fueling only works at the stoichiometric or "perfect" AFR. Any other AFR like power enrichment or lean cruise must be done in open loop.
It is possible to bias the system toward a leaner mixture if you have a NB sensor. While the system is designed to swing back and forth across stoichiometric, the high, low, and center points of the range are often adjustable. By lowering the high point you don't let the engine swing quite so much to the rich side before it has to go back to lean. By lowering the center point the ecm will target a leaner AFR. Remember that the farther you go from stoich the less accurate the sensor is.
Also keep in mind that using 10% ethanol fuel throws off stock settings. The stoichiometric AFR for 10% ethanol is 14.04:1. The ecm will target your gasoline based AFRs in open loop, but in closed loop it is forced to deliver more fuel than calculated due to O2 feedback. Stock OBDI vehicles using ethanol fuel usually show BLM higher than 128 due to the fuel itself. For a vehicle which consistently uses ethanol fuel I like to change the stoich AFR so the BLM's come into line before adjusting the O2 limits. If you tune using ethanol fuel and you don't adjust the stoich value, the correction will accidentally get built into the VE tables.
I heard the 10% ethanol thing too. Problem is here in Oregon and probably in other places the sticker says it COULD contain up to 10%. I had my tables really close drive, after drive, then filled up as the same station again about a month later. It threw the whole table off. Its just a small amount but enough that I started to look into it as it was bigger than just the change the weather makes. Seems like I am not the only one. Other forums have a lot of threads like this. They sometimes suggest splitting the difference and setting the narrow band to 14.4 as 3% - 5% is not hard to find from the nozzles of pumps labeled as up to 10% At least in Oregon, there is no fuel law that states it must have a certain amount, only that it could.
I use 14.1 myself. I prefer my fuel trims to stay slightly on the low side. If you calibrated the fuel map on a tank that had say 5%, then added in fuel that had 10%, you would be running lean. We have E15 in a lot of stations here now.Quote:
Originally Posted by donf
Yes that's the idea of splitting the difference. Middle ground keeps the correction required with either E10, or Ethanol free fuel, within the a reasonable adjustment range and not biasing it one way or the other. Sounds like its a regional thing on E15, Ethanol free is still very common here. I looked up Oregon's law. They still have pump gas set at up to 10% allowed, but it could contain 0% out of the same nozzle next week. Pump gas with 15% would require a state law change here. There was a big uproar about E10 here, some people still will not buy it, not sure any E15 changes will pass.
This is probably only a personal preference thing, but I prefer to stick to the rich side and let the 02 sensors pull fuel if it is not needed. If you are adding fuel at light throttle the PCM will keep adding the same amount at WOT.Quote:
Originally Posted by donf
You could, and I have even done it to be just a little richer once since I had a car where I could feel the lean side of the AFR as the closed loop fueling oscillated. But, if you go very far then you can't change the O2 sensor without re-tuning it since they are only repeatable sensor to sensor right around stoichiometric.Quote:
Originally Posted by 1project2many