RamAirRocket

iTrader: (1)

I know this is probably too simple of a question, but here goes....

I am tuning my LT1 OBD1, and while I am datalogging, I see it shift between certain cells. 6, 7 or so at cruise, 16 at idle. Obviously different conditions get a different cell.

Now, I am messing with open loop tuning to get a lean cruise setup and evaluated, and it now stays in 18 at cruise, 17 when I am accelerating, 16 at idle.

What does it mean when it is in a cell, and what is actually IN that cell?

Can I edit the cells directly and change how it fuels in those cells?

Thanks!

white2001s10

iTrader: (4)

The value in the cell is the fuel correction as a % that gets multiplied into the fuel equation.
If you're in open-loop tuning, then you should clear (zero) all the BLMs before you start tuning.
The BLM's are only for closed loop running.
You still hit the cells in open-loop, but no corrections are calculated during open-loop, so if they have been cleared you will get no fuel corrections and the BLM's should stay at zero.

I think most people edit the VE table to make fueling corrections.

RamAirRocket

iTrader: (1)

How do I clear the BLM's on a LT1 PCM? Where are the memory locations in the bin file that I need to find, or where might I find them?

Primarily in Closed Loop (when I have it enabled) I am in 6 at cruise light load, 10 for cruise moderate load (like hills), 11 if more power is needed, and 2 on decel. If I nail it and get up faster, I am in 3 for decel until rpms get down and it drops to 2. As always, this is a VERY general how it works, it is all over the BLM's depending on what is going on.

So, in theory, could I change the load cell 6 to remove some fuel to make slightly leaner?

white2001s10

iTrader: (4)

With the older TPI systems you only need to unhook power to the PCM for a short time to clear the memory. BLM's were not stored in the .bin file, but were in the ECM memory.

Most people do their VE table tuning based on the fuel correction numbers in various load cells, so I'd have to say yes it's possible.
It's even possible with some software to re-define the boundaries of those load cells to better match your combination or driving style.

RamAirRocket

iTrader: (1)

I can tweak VE tables, but from what I have heard, they are not used in closed loop. I can't confirm easily.

So essentially the BLM value isn't really a memory location in the .bin where the PCM is looking up information? It is more of a value that the PCM determines and that number is a offset? Sorry, I am not getting very well.

How does one recalculate VE values?

Thanks!

white2001s10

iTrader: (4)

The ".bin" is the binary file that loads into working memory. The BIN is the code or program that runs in the ECM/PCM.

The blm corrections or LTFT (fuel trims) are not part of that file, but they also exist in memory locations inside the ECM/PCM.

The running code stores calculated fuel corrections (the BLM's) into these locations. These correction values are stored as a percentage to be factored into the fueling calculation before activating the injector driver circuit with the final value. The code looks at these memory locations to retrieve these values as needed.

These values stay in memory when you shut the car off and keep getting used until either the ECM updates them to new correction values, or you remove power from the ECM/PCM. Some scanning software gives you an option to clear the fuel trims instantly from your laptop.

Usually you will be in the ballpark by using straight percentages when changing VE values. For instance if you're 10% too rich and you have a VE value of 100 you should be in the ballpark by changing the VE to 90

RamAirRocket

iTrader: (1)

So if felt I was running rich at say, 2000 rpm at 0.5 KPa, then I could remove 10% VE from that cell and it would lean accordingly?