BLM cell, BLM #, VE table??? - Third Generation F-Body Message Boards

Keith91sub · 10-02-2009, 01:27 PM

As I am hopefully learning more and diving deeper into tuning I have a question/discussion related to the interaction of the BLM Cell, BLM readings, and the VE table.
If I understand it right, there are 19 cells that make up the BLM Cell table. Is that to say that there are only 19 learned BLM numbers at any given time? For Example: By observation, I see that at cruise the ECM is typically in cell 5. I also see that within cell 5 (holding a steady throttle) I could have a nice steady Integrator at 128, then if I change load (speed up or slow down a bit but still in cell 5) the Integrator will drop/rise and pull the BLM down/up. What this tells me is that my VE table is not optimized in the range of Cell 5 – Is that correct? Is it that each BLM Cell has a range of VE points and those VE points each have to be optimized for a 128 BLM reading? If not optimized, as you change load within a BLM Cell the integrator/BLM will always be running up and down to correct fuelling.
If what I am exploring above is correct, then I think that I have discovered why I have been having a difficult time stabilizing the Integrator/BLMs at certain points. I have been chasing a stable setting at low RPM/Loads but probably only looking at too narrow a region of VE cells. As I chase 128 in one part of a BLM cell I do not correct the rest of it, so the integrator is constantly running up and down.

Hopefully I am on the right track with this. I am looking for feedback so that I can continue to learn more about how these systems are designed and operate.

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bl85c · 10-02-2009, 08:10 PM

There's 16 BLM cells. The way the rpm/load constants are set determines how those cells cover the motor's normal operating range. Not all are used either, only 5 are typically used and even then only 2 are saved after shutdown. There's no dedicated connection between the ve table and blm cells, the two simply overlap based on the rpm/load constants used. When you tune the ve table you tune every entry not groups based on what blm cell it's in, although that would be a good way to rough in a tune. Tuning needs to be done steady state in each entry (which is why an emulator Kicks a$$) until it's 128/128 everywhere. The tune will vary a bit based on weather so most people won't tune closer than +-2 counts. You might lock the blm to 128 and just use the int to make tuning a little simpler.

doc · 10-09-2009, 11:07 PM

As given above, there are 16 fuel trim cells (FTC). They are arranged in a 4 x 4 pattern, based on engine RPM and MAF air flow. Now, I am tuning a MAF car, your FTC boundaries might be set up on engine RPM and engine load, if you are tuning a speed density car. There is a unique BLM and INT value for each FTC. The ideal values or baseline is the value 128. If you have BLM values between 122 and 134, consider your ECM tuned perfectly. For you, a higher VE value in the VE table will add more fuel, while the opposite is true. Therefore, if you have a BLM value of 155, the ECM is adding value on top of the base fuel calculation, to get you to stoich. In order to bring the BLM value down closer to 128, you should increase the values in the VE table that match up with the FTC that is at 155. Also, it is important to note that the BLM value is kept in memory for the next startup, while the INT value is set back to 128 when you shut the engine off.