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.

 

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.

 

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.

 

I don't fully understand Fuel Trim Cells. Is there an actual table in an OD bin where these values are viewable or is the table generated by a lot of individual constants that the PCM uses to costruct the table? Is there ever a need to edit the Fuel trim cells or is all of the editing accomplished in the 2 main fule tables?
Thanks, Charles

 

The table is created virtually in the ecm's memory, so there really isn't a viewable table. Changing the load and rpm points changes what part of (and how) the table covers the operating range. You can better cover how you drive by changing the tables and potentially get better mileage, create cells for acceleration, deceleration and whatever else you can think of. Takes alot of experimentation to get what you're looking for.

 

Thanks for the quick reply. In datamaster there is a value that show which cell you are operating in and it will turn yellow if it jumps too far too fast. So, what is the importance of watching which cell you are operating in, in other words how do you interpret and use that data in your tuning?
Thanks, Charles

 

The number of the cell is unimportant, it's just a name. IDK why datamaster's set up like that. What's important is the portion of the operating range that that cell covers. This gives you a good tuning aid when you're roughing in your ve table or maf tables so you can tune larger areas quicker, then get each individual point tuned that much easier. After you have the blms nailed down you can change where the blm tables cover so you can create specialized cells to cover events like closed throttle decel where fuel's pulled off the port walls and the motor goes rich. Sometimes you need a specialized cell to cover events you can't cover with the tables, especially with maf.

 

If I can't see the table how do I control where in the table I am operating? When you say load and fuel are you talking about fueling and vacuum? And how do you create a specialized cell if you can't edit the table. Sorry, I don't follow. Is it right in front of my face and I am missing something or is it not that obvious.
Thanks, Charles

 

There's 2 tables -although each value is usually listed individually-, one for rpm and one for load (either LV8 or map) that together define the the blm matrix.