So do the folks running highway mode on '165 MAF setup get close to their actual target AFR? This is of course is testing with a WB. eg if my target AFR is 16.80, i get LM1 data of 16.08. For all my readings, the WB AFR numbers are running lower than the target, by almost a full point. Now when I am not in HWY mode, the WB bounces around 14.7, but my BLM is holding around 140. Now I know that is a bit on the lean side........so maybe i need to get that more inline with 128?

 

It's usually pretty close for me, but it's less accurate the further you get from where the last correction factor was saved in a particular blm cell. Eg. if the last correction was done at 1500rpm in cell 10 and you're at 1700rpm in cell 10 it will run a little leaner.

 

If your BLM's are within the ajusting range 108 to 160 then your AFR will be at the 14.7. When the intergrate hits 128 you should be at the 14.7 AFR. The more and less then 128 is how much the ECM is adjusting to get back to 14.7 AFR.

Which is the center of the O2 swings, more or less.

 

My integrator is right at 128, but like i said the BLM was steady around 140, during 2 different road scans. And my O2 was swinging just fine. FYI, i used TP RT for these scans, but for long time i was using another scan tool, to do all my part throttle tuning, and thought I had it close. So should I adjust things to get my BLM back down to 128? Will that help my highway mode AFR? I think what I will do first is pull out my old scan tool, and see what the BLMs are with that tool.
Keep the ideas coming!
Mike

 

I would like to know also

 

You can if you like, but like pandin said all the 128/128 model means is that the ecm's original calculation is accurate with how it's actually running. If it's at 140 it means the original calculation was lean and it had to enrich it to get it to stoichiometric. Theoretically the ecm should always produce stoich regardless of what the blm/int are doing. In the real world weather, engine condition and fuel quality are constantly changing.

Furthermore, the blm cell matrix is just too coarse to keep the engine exactly where it needs to be without having to readjust some from cell to cell, but it gets close. This is partially why you get some funky numbers sometimes in open loop conditions like highway mode. Any time the ecm tries to produce an afr other than stoich it's done as a set deviation from stoichiometric. So it will take the correction factor (blm) recorded in a particular cell and adjust that calculation by whatever % it's trying to move from stoichiometric to produce another afr. So basically it's a calculated guess adjusted by another calculated guess adjusted by another calculated guess... which is why I think GM dropped highway mode. Just too many adjustments to really be accurate long term.

Matter of fact if you want to see how crude it acutally is set the blm cell rpm limits to something like 1000, 5000, 5000 (to force it to refrence strictly airflow) and watch afr changes alongside blm cell changes and see just how dramatic it can actually be.

I just make sure everything I put into the ecm is as accurate as I can get it and let the ecm do it's thing.

 

Ok, today got back into this stuff, after the long weekend. Did a road test scan today with my old scan tool from Ease Diag. And once again found my BLMs to be around 140. I hadn't changed my chip yet.

So what you are saying, bl85c, is that if the ECM needs to calculate the fueling for a different AFR than 14.7, it takes the current BLM reading and makes some calculations? Normally it thinks that 14.7=128, so if you are off that, like 140 is 14.7, then to adjust that for a different commanded AFR, eg 16.8, than your actual AFR will be off, since your BLM is off.

tonight made a small change in the chip, to see if I can get my BLMs back down. I havent done any global changes in a while, and like you said many conditions affect the numbers. Maybe the fuel i am using is different. I know they have added Ethanol to many brands lately....

 

Yes and no. The ecm uses the blm/int to correct the base calculation to get stoich. Then the ecm will offset that calculation by whatever factor is specified to get you to whatever afr other than stoich it's trying to achieve. Different masks have different ways of doing this as well. Some have a lookup table where gm engineers had to test to find that XXX% change equals whatever afr they want. Other masks have a table that specifies the desired afr at whatever running condition and does separate comparative calculations to arrive at the calculated % change needed to deliver that afr. Most highway enleanment tables I've seen specify desired afr. Theoretically it should deliver the desired afr regardless of where the blm is because it should achieve a baseline afr (stoich) from which every other afr is achieved, but things get skewed in the real world especially after being readjusted so many times.

Round and about way of saying that it's supposed to give you whatever afr you specify regardless, but it's just not accurate enough. You may benefit from adjustments because of this innacuracy. Infact that's what tuning is- correcting the slop and inacurracy in a theoretical system.

 

Ok, I sort of get it. Just might not be that easy to get my desired HWY mode AFR correct. I don't know much about many other masks, but I do know that some of them had the HWY mode code in there, but GM didnt enable it! Like they had all the min parameters to enable set so high that it would never kick in. I suppose i could just set my HWY AFR table values more lean, to really get the (LM1) WB values that I want. Just gotta be carefull with that!
Otherwise, no matter if my BLM correction doesnt help the HWY AFR, it is still a good thing to have them running around 128. Like I said before, I used to have them avg around 128. But something must have changed lately. I know I have not done anything new to my engine, that for sure. Maybe it is the fuel. Could the plugs be wore out?

 

One way to find out.