Why is it important to dial in the VE (to get 128 BLM's) as opposed to just letting the ECM do its own learning? Doesn't the ECM generate a table to work from? Once it's done doing that how is it different if the table is full of 128's or 150's?

A possibly related question: when I log BLM data using TunerPro, it looks like the first time a cell gets a BLM reading it's always 128, then it moves as the cell is observed more times. Is that just my imagination? If I've been driving the vehicle for months, am I not just reading out long standing BLM values?

Thanks for any help, I'm trying to understand how this stuff works.

 

The BLMs should be as close to 128 as possible. There are several reasons for this. The engine will run smoother and be more responsive. Also if the BLM is > 128 it will also be used during WOT.

Some ECM masks only have 2 BLM cells, others 3 cells, while others have 16 cells. So the resolution compared to the VE table is course. Going from a lean area of VE to a rich area of VE will be rough as the BLM takes time to adjust.

Some masks reset all of the BLM cells to 128 at key-on ($61 in particular). Others will only save two of the cells while the remaining cells get init to 128 at key-on ($6E & $8D). With the saved ones being high & low limit checked at key-on.

RBob.

 

Oh, so the big thing I might be missing is that the VE table is much bigger than the BLM table. How many BLM cells are there in a 7747 ECM? Does 7747 reset at startup? Thanks!

EDIT: I think I found that the BLM is 3x3, 9 cells. Not sure about the BLM reset still.

 

'7747 is 4x4 for 16 cells. It is one of the masks that does an upper and lower limit check/set at key-on.

RBob.