TriPinTaZ

OK, as we all know our pcms have 16 BLM cells. I alredy know how they function, but I am curious if they affect the PCM in open loop mode. I run an open loop only tune in my PCM and my scan tool shows the BLM cells vary at differnt engine RPMs and MAP. But since my PCM ignores my O2s all the time do the BLM cells do anything?

EviLBoX

I've been using OBD-2.com software to scan my car and in open loop the BLM's are locked at 0% or 128. LIke you said, since the O2 sensors aren't used, I don't think the BLM's jump around.

DOOM Master

I think they might have a minor effect, but only because I've seen the cells change and the Lterm numbers are slightly different between the cells sometimes (this isn't very common, and usually it is only a point or 2 off from 128, like 129 or 130). The PCM might make a slight fuel correction based on the Lterms that it has been commonly using during closed loop. Does it really have an effect? I don't know, but it's something I'd like to know more about.

TriPinTaZ

my BLMs are locked because of the open loop mode. I know the BLMs do not actually adjust at all. But my scan tool reports the pcm is entering different BLM cells. ( 1-16) liek at an idle im in BLM cell 16 but there is no LT or ST fuel trims. I just wanted to make sure that the scan tool is just showing what BLM cell the car SHOULD be in even tho its not making any corrections.

TriPinTaZ

Long term and Short term fuel trims are not used in OPEN LOOP mode. I just wondered if anyone here knew for sure that even tho my BLM cells are changing ( 1-16) that it plays no roll in an open loop tune. I know for a fact there are no fuel trim learns active in my PCM. I want to hammer out a few "RULES" that I am finidng in the PCMs operation from open loop vs closed loop on my next endever to try and run a closed loop tune on a 260/260 solid roller

I have been thinking about trying to go back to a closed loop tune, but everytime I do this my BLMs are split. I have actually pinpointed the cause of this. it is because I have my throttle blades cracked open, I need to do an IAC mod and close my throttle blades and work the tune from there. The closed loop tune was always great under load but at idle went way rich no matter what and my BLMs were split. Now that I have found the solution I am going to attemp a 3rd try at closed loop operation before I ditch the whole PCM for a DFI 7 unit.

Injuneer

In the stock setup, in open loop it only runs in Cells 16 (idle), 18 (load), 17 (coastdown). It doesn't use Cells 01-15. The BLM's for Cells 17 and 18 seem so be "calculated" from some combination of the "closed loop" cells.

Dan K

Have you tried using a pe based idle?

TriPinTaZ

yes, it caused stumbling

97Z-M6

if you are seeing are lt blm of above 128 (showing a lean condition) but not acctually lean because the pcm is correcting for it, that lt blm is used in the final calculation for pe mode. it will add fuel becuase the pcm knows if it wasnt correcting for the lean condition, you would carry that lean condition into the pe mode at wide open throttle, if it didnt add the corection factor that it has been using while under normal conditions.

this is why alot of people tune the blms to about 125. so when you go into pe mode the blm is below 128, so this way the pe mode is not affected by the lt blm number, and you know what air fuel ratio its running (basiclly you know what you have tuned it to be.)

there is a long eqaution for for all the factors that the pcm uses to determine the final A/F ratio at wot. ill see if i can find it.

Dan K

Are you sure it's going rich at idle?
I thought a car I was tuning was doing the same thing and was wrong. It was way lean. A/F was between 17:1 and 20:1 at an idle. I have not been able to get it down either.
Set it up to idle in PE mode and it helped a little but not sure if it was worth the time.
Seemed strange to me. I wonder if you're experiencing the same thing and whether it's due to valve overalp?

TriPinTaZ

my car is definatly not lean at an idle. After data logging it even tho the O2s are showing somewhat split BLMs at an idle the injector pulewidths are the same. and hte car runs fine. I think im going to scrap the closed loop idea and buy a wideband setup and keep my PCM in open loop