How do you pick a bin to start out with?

[damanx]

I've been using the TBI calculator V1 spreadsheet to adjust the BPW and VE tables.

I've noticed that even with the course adjustments to that, I've seen that it seems it takes several adjustments to get close to 128, but then later realized that +/- 6 is probably close enough.

Am I correct to assume that if the spread on the BLM values are pretty close, (i.e. all cells are say running 122 for example), that changing the BPW would be better since it seems that would be more or less a global change and not specific?

[RobertISaar]

BPC is really a fudged fuel calculation method anyways..... you kind of have to work backwards and do some educated guessing to find out what it should really be set at.

too high or too low, yet still within correction range of the VE table(s) will cause the actual AFRs to not meet commanded AFR when at ratios other than what the VE table was tweaked in at.

i really don't understand why GM chose to go this route other than it being a comparitively quick and relatively low memory method compared to doing an actual volumetric efficiency -> airmass in cylinder calculation. i can see why it was used in the C3 programs, but it held over into P4(and even P6, i think) for a lot of applications.

[Six_Shooter]

+/- 6 on BLM is pretty good. You will NEVER get an engine to run at 128 in every instance at every point in time, NEVER. A change in air temp changes fuel required, a change in elevation changes fuel requirements, a long with a bunch of other stuff we can't really control.

Yes, if you find you are consistently low, as in your BLMs seem to be centered around 122, then adjusting the BPC/BPW can move the BLMs to be centered on 128, usually. I have had a couple of times where I could only seem to get the centering to be on like 126, otherwise it went way out of whack.

Tuning is all about compromises.

[steveo]

if your blms are 122 or 120, and you aren't a picky bastard like me, just leave it alone. it's OK to start rich and let it trim out. oooh oh my god im going to run 14.3:1 and burn 3 cents more fuel every time i cold start it. who cares?

[damanx]

For whatever reason, and I should not say "whatever" as if I wasn't sure, I tend to be on the side that likes to be almost exact. Where I work, we are adjusting electrical parameters that are typically in the micro ranges. Problem with that is that there is usually a limited amount of time to make such adjustments and move on.

I've got to get past that with this stuff too.

[steveo]

you must understand in a threshold controlled open and closed loop control system of any kind, it's always best to start with a particularly safe margin of error when in open loop, and let the control system correct towards ideal, rather than be right on the mark, or worse.

that's exactly what you're doing here, starting safe, and letting the system make it perfect.

blms over 128 bother me. blms around 120 are nothing to worry about. and usually the engine is only in open loop when it's cold, when a bit of extra fuel sure wouldn't do it no harm.

no engine minds a bit of extra fuel. as long as closed loop corrects for it, it's ok.

it's possible to get it fairly perfect, but due to how a system that starts in open loop and enters closed loop later works, it's almost better to have it tuned a lil' rich and live with it. some day when you get a clogged fuel filter or something, that bit of extra fuel might be a good thing too.