BLM & INT - could someone confirm how they work?

[tony-baroni]

I am looking for confirmation of how the GM BLM and INT values should track once the vehicle is in closed loop mode.

From what I've seen online BLM is the long term fuel trim and INT is the short term fuel trim. However when I look at these values as I drive my vehicle, or watch logs afterwards, the BLM resets itself back to 128 even after drifting fairly far from that number, quite frequently.

Are BLM and INT single short term values, like shown in the Dashboard? Or are they table based values?

If they are table based, is it based on engine RPM? And where can I view them?

The reason I ask is because it looks like BLM is resetting, I wonder if it's a problem with my ECM (faulty memory?).

Thank you.

[Mangus]

Fuel trim is stored in a course table that overlays the fuel table. One of the ALDL output values is "Fuel Trim Cell" (may be names slightly differently in each definition). This tells you what trim cell the vehicle is running in. The long term trim (BLM) value for that area of the table is stored in that cell.

INT, the integrator, is the short term value. It's the number that's actively used to correct the immediate rich/lean condition. Over time, BLM tracks with INT. Once stoichiometric has been reached, you should see INT hover around 128, though BLM may be far off of 128. This is basically the ECM saying "With BLM at X (e.g. 100), no further correction to fuel is needed to reach 14.7:1, therefore INT is centered at 128."

If BLM is resetting, i'd think you're either leaving closed loop, or the trim cell that you're running in doesn't have enough data to move BLM.
_________________
***************************************
TunerPro Author
1989 Trans Am

[tony-baroni]

Thank you Magnus. Is it possible to view the fuel table and the BLM 'fuel trim cell' table in TunerPro?

I'd like to use the BLM table, as a tool to further tweak the fuel table over time.

Anthony

[Mangus]

The data isn't directly exposed by the ECM. The best you can do is create a histogram with RPM on one axis and LV8/MAP on the other, and BLM in the Z axis. Then do some logging.
_________________
***************************************
TunerPro Author
1989 Trans Am

[tony-baroni]

Magnus,

Can you share how to create those histograms? The help section ADX Histograms in my tunerpro SW is empty. I just updated to the latest version as well.

Thanks

[tony-baroni]

There is a tutorial I found at gear-head efi for creating these tables. In case anyone else is following this thread I am posting it here:
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?444-Making-History-Tables-in-TunerPro