Stevie

I'm still learning about my code (slightly modified AUJP) and I'm trying to get smart enough to tweak the VE tables. So I'm studying the data I have collected and I notice that the BLM cell it is running in seems to have virtually no correlation to the cell edges (rpm and kpa). For instance, at idle generally I'm running around 45 kpa and 700 rpm. The way I read it I should be in the area of cells 8,9,12 or 13. But it actually stays mostly in cell 4 at idle. Is there something im missing??

SMasterson

Cell 4, for whatever reason GM decided, is the idle cell. I've read where different types of PROMs use other cells.

There are certain things you can change in the PROM that will cause you to get *stuck* in cell 4. Canister purge setting is one of them and I believe VSS is another, not sure. (Not your problem since you seem to be switching, just not very much.)

I have edited my cell boundrys so I used more BLM cells since I idle at 65kpa and cruise at 50-55kpa. I end up using about 1/2 of them and it makes throttle transitions a little smoother.

By using more cells and letting the ECM learn the BLM values thing are smoother because the INT starts at 128 when the ECM changes cells anyway, then it has to fine tune from there. If a condition changes that would cause the INT to swing from one extreem to another, without BLM learns driveability would suffer until the INT got the fuel back where it thinks it's supposed to be at.

Clear as mud. Actually, I either don't understand it at all or I just have trouble communicating it in writing. Either way, my tuning works well for me. Through many many chips, now I can usually predict what my changes will affect, and how.

Stevie

Thanks, actually it does make sense. Yes, mine changes cells just fine (as far as I can tell) and the BLM's are generally in the neighborhood of 128. Except for cell 4 which spends much of its time at 108. I havent tweaked the VE tables at all, cause I havent figured out how it all ties together yet, but I'm working on it. Another confusing part of the whole thing is that the original GM cell boundaries are at 28, 36 and 45 kpa when my engine seems to spend 90% of its time above 40kpa. Those boundaries seem useless. Does everyone usually move those to higher values?

Grim Reaper

When my engine was bone stock, I found the following BLM Thresholds worked well

MAP - 39, 58, 74
RPM - 850, 1400, 1800

I found these settings tended to use the most BLM cells for my normal method of driving when my setup was bone stock.

Stevie

Yeah, those numbers look a lot more reasonable for mine also (stock 350 with a mild cam). Ill give them a try. But the part that I still dont get (sorry, I'm a little slow) is that the VE tables are indexed only by RPM and MAP. What's the point of cell numbers?

Regardless, in my case my cell 4 BLM's are all 108....This means rich? So do I go to all the VE table entries that fall within the cell 4 boundaries and tweak them?

TRAXION

jason_c posted this on another board after grabbing this image off TGO. It's taken directly from the ANHT hack and clearly shows the breakdown of BLM cells as compared to RPM and MAP. This idea has been around for almost a decade now. Nothing new ... but very important.

Tim

Stevie

Thanx Trax...

I have seen that pic of where the cell edges are set. Actually, I've spent quite a bit of time wading through the ANHT hac. But one thing still hasn't sunk in for me. That is: Correct me if im wrong here. I know this is an oversimplification. In normal operation (closed loop, etc.) the ecm goes to the VE tables and at any given RPM and MAP finds a number which correlates to an injector pulse width. I can hear you experts howling out there. The ecm then changes the BLM no's which are used to adjust the pulse widths until you are running at stoich.

So if this is mostly true, then where are the cell numbers used? If the engine is at 2000rpm and 50kpa does it matter whether that is cell 11 or 14? And if I change the boundaries of the cells to where I am using more of them, has that changed anything in the operation?

Steve

RBob

iTrader: (1)

Nope, no change in operation. The BLM cell matrix is used whenever charcoal canister purge is active. It allows the ECM to correct for, then change among the cells for the smoothest operation and least emissions. Whenever CCP purge is active the fumes affect the various RPM ranges and manifold vacuum ranges AFR differently. This is due to a different volume of and/or different density of the fumes at these different operating points.

RBob.

novakm

This is real interesting. I have a 7730 AUJP ECM.

My BLMs and INT's do not seem to act correctly. I use ECM852, and I NEVER see a BLM cell reported other than #4. I just assumed the ECM852 software did not read it right.

Now I'm wondering, maybe I really am stuck in BLM cell #4? How can I tell for sure?

what canister purge settings can get you stuck? ( I've messed with mine because I do not have a canister). How about VSS? The ECU also does not get correct gear info, since I have a TH350.

Mike

novakm

OK my bad

Found the BLM locked posts in the stickys above...

1bad91Z

iTrader: (1)

In reference to the above chart, I have a couple of questions on setting these boundaries to "fit my motor's needs".


My car idles at 850 rpm's (dont remember the kPa). So, once I change the CCP % to 0 , and I'm no longer in cell 4, does this mean that I'll never hit cell 4 again due to idle is higher than 700 at the 1st row's Kpa ?

What value's should I set BLM MAP and Kpa boundaries to? I guess I'm still a little confused on how to make the ECM hit all the different cells.



Again, forgive the ignorance on my part!

1bad91Z

iTrader: (1)

Anyone?

TRAXION

Tell ya what ... hehe ... let's play multiple choice.

If there are BLM cells for BELOW 700rpms and if your car idles at 850rpms then ....

a) Your car idles higher than 700 so the ECM never sees a sub 700rpm idle and therefore never uses those sells
b) Your car explodes
c) The ECM sees an 850rpm idle and then speaks to you in tongues to inform you that you must change your idle
d) b and c
e) all the above



Tim

1bad91Z

iTrader: (1)

Since my car acts like it's possesed at times, I'm gonna have to guess choice C.

Ok, I understand my car will never see cell 4 now. However, you said to set the MAP and KPA boundaries to allow the ECM to enter as many cells as possible by tailoring it to fit my motor.

I'm still a little in the dark on this.

Also, if I never see cell 4 again, is this ok? Are there other cells that I should avoid, or is the idea to set it up that way the ECM can hit all the cells?

Sorry for the constant questions (no pun intended) and thank you again for the continued help!

Mike