On a cold start the INT is set to 128 and kept there until the coolant reaches a threshold value, a timer says the engine has been running long enough, and the O2 sensor has warmed up and started responding. Below 128, and it represents a correction for a rich condition. Above 128, and the ECM is adding fuel to compensate for a lean condition at a particular load and RPM. 128 is the ideal value, because it is the center point of the range 0-255. The BLM is a long term adjustment, which is stored pretty much permanently (unless you disconnect power to the ECM), to the fuel delivery calibration that results from the ECM "learning" the values while you are driving around.
In this example the ECM will be using cell 15 (sometimes erroneously called the WOT cell) (WOT meaning Wide Open Throttle). Typically when you pull away from a stop sign or traffic light in fairly normal circumstances, youll see that it takes only a second or so for the RPM to jump over the 1500 upper RPM limit, and the MAF (air flow) will very easily jump up over the 30 gps upper MAF limit. Cruise conditions will often move between cells 7 and 11 based on small changes in MAF, since the typical highway cruise value is between 15 and 25. Since the RPM is above the highest value in the column to the right, and the MAF is reading a value in the third row, we can see that the ECM is now accessing, and using the BLM value in cell 11. Now, lets go for a typical highway cruise, at about 65mph, on a nice flat road: The value contained in that cell is adjusted with the Integrator values (which change based on O2 readings, etc.). Since the RPM is very low and the MAF is very low, the car will be using the information in BLM Cell 0 to adjust the idle fuel mixture. Let's say the car is sitting in the driveway in Park, up to temperature, and just idling. So, the cell being accessed at any given point in time is controlled by airflow versus rpm. The individual cells are numbered 0 through 15 (for a total of 16 cells). As you can see, it is offset by rpm in the columns, and by airflow in the rows. The table above depicts the BLM cell table that is held in the typical Turbo Regal ECM. For both the Integrator and BLM values, a higher value represents a correction that adds fuel to the fuel mixture, due to higher injector pulse widths. Each BLM value in turn contains an integrator value (also from 0 to 255), which is a short term fuel correction based on immediate operating conditions. Each cell contains a Block Learn Multiplier (BLM) value (from 0 to 255), which represents a long-term fuel correction based on that cell's operating conditions over a relatively long period of time. The fuel delivery strategy uses a two dimensional table that has four rows and four columns, for a total of 16 "cells". In our ECM the Long Term fuel adjustment (BLM) happens about twice per second, while the Short Term fuel adjustment (INT) happens about 20 times per second Basically, these two strategies are used to make adjustments and adaptations to the ever changing loads, atmospheric conditions, and fuel quality to keep the car's air/fuel ratio correct for driveability and emissions.Īlso, keep in mind that when we say Long Term or Short Term, we are talking in computer time, not human time. The Integrator is the same idea, only for short term adjustments. In a nutshell, the Block Learn Multiplier (BLM) is the long term fuel adjustment that the ECM "learns" to keep the air/fuel ratio within acceptable parameters.
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