Tuning with BLM vs BLM+INT
08-22-2004, 11:08 AM
#1
Tuning with BLM vs BLM+INT
I was thinking about BLM tuning... A BLM "cell" covers a number of VE "cells". So if two VE cells in the same BLM are off, but by different amounts, then every time you move from one to the other while taking data, the ECM is going to start pulling the BLM in a different direction.
Say, for example, one VE cell "wants" a BLM of 120, and another wants a BLM of 140, but they are both contained in the same BLM cell. Unless you can stay in each of them for long enough to pull the INT to 128 while capturing data, then you'll never get good BLM numbers to tune from. If you switch between them while driving, the BLM will always be in a state of flux.
If you take BLM and INT data and can see 128 INT in a VE cell, then it seems like the associated BLM value is good to use. If the INT is off 128, then at the very least you ought to fudge the correction in the direction the INT is pushing.
I've noticed that when I come to a stop and idle, my BLM starts going up in the cell where I idle. It seems to do this all the time. This was one theory I had, that the BLM is shared with other VE cells that are wanting a smaller BLM.
This doesn't mean I don't have some other issue, but it illustrates a potential issue with BLM tuning.
Say, for example, one VE cell "wants" a BLM of 120, and another wants a BLM of 140, but they are both contained in the same BLM cell. Unless you can stay in each of them for long enough to pull the INT to 128 while capturing data, then you'll never get good BLM numbers to tune from. If you switch between them while driving, the BLM will always be in a state of flux.
If you take BLM and INT data and can see 128 INT in a VE cell, then it seems like the associated BLM value is good to use. If the INT is off 128, then at the very least you ought to fudge the correction in the direction the INT is pushing.
I've noticed that when I come to a stop and idle, my BLM starts going up in the cell where I idle. It seems to do this all the time. This was one theory I had, that the BLM is shared with other VE cells that are wanting a smaller BLM.
This doesn't mean I don't have some other issue, but it illustrates a potential issue with BLM tuning.
08-22-2004, 12:45 PM
#3
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Car: 89 Shortbox
Engine: 350 Vortec
Transmission: 700r4
I tune via the O2 mv readings in open loop, with the ecm reset (unplug for a few seconds before driving), so that the blms are all 128.
I noticed that when tuning via the blm, and modding the VE cells that way, when I graphed my VE table it had lots of little peaks, and wasn't very smooth. And what your saying about 2 VE cells "fighting" each other with the int is true.
I noticed that when tuning via the blm, and modding the VE cells that way, when I graphed my VE table it had lots of little peaks, and wasn't very smooth. And what your saying about 2 VE cells "fighting" each other with the int is true.
08-22-2004, 06:09 PM
#4
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I've noticed that when I come to a stop and idle, my BLM starts going up in the cell where I idle. It seems to do this all the time. This was one theory I had, that the BLM is shared with other VE cells that are wanting a smaller BLM.
08-22-2004, 06:13 PM
#5
Originally posted by onebinky
If it's a MAF car, you might want to look for any false air entering the motor after the MAF. At idle, that will make the BLM's go higher because the engine is getting air that the MAF doesn't see.
If it's a MAF car, you might want to look for any false air entering the motor after the MAF. At idle, that will make the BLM's go higher because the engine is getting air that the MAF doesn't see.
