someone please explain ECM learning
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
The ECM has a table of coefficients (called BLM, Block Learn Multiplier) for different conditions such as engine speed, vacuum and temperature. These determine the coarse value how much fuel should be injected in given conditions. The optimum coefficients for a certain car are learned by the ECM by monitoring the oxygen sensor voltage (rich or lean) in the given conditions. This is usually a very slow process. There is also a faster changing variable for fine-tuning the amount of fuel, called the integrator.
If the integrator goes out of range for more than a specified time, then the Service Engine Soon light may be lit, and/or the BLM coefficients adjusted. However, if you reset the ECM, it has no memory of the history of whether the car ran rich or lean with certain BLM values, so it goes into a learn mode to quickly determine what BLM values should be used.
If the integrator goes out of range for more than a specified time, then the Service Engine Soon light may be lit, and/or the BLM coefficients adjusted. However, if you reset the ECM, it has no memory of the history of whether the car ran rich or lean with certain BLM values, so it goes into a learn mode to quickly determine what BLM values should be used.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 414
From: WV
Great explanation rodj. When I dissconnect my battery and clear the ecm, it takes at least 1/2 hour of driving before its running completely normal again. So it does take quite a while to relearn....WW
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Somewhat of a misnomer - it's allways learning. ECM's/PCM's have RAM with essentially 2 functions: Trouble Codes and Long Term Fuel Trim. Learning refers to long term fuel correction which can change anytime you drive it. Once you turn it off, that's stored in memory which facilitates restarting, and if nothing has changed since you turned it off, correct fuel delivery. Starting out with nothing; ie, you've cleared the RAM by removing power, means that it's starting from scratch. In terms of time, it's operating in nano seconds, so this isn't something that's going to take an eon to accomplish (under most driving conditions), and there are situations where it's best to start over - repairs/replacement to any information sensor or wiring for example.
Melting Slicks
Joined: Aug 2003
Posts: 3,418
Likes: 406
From: Lakeville MI
There is also some learning capability for the idle PID controller with respect to A/C on operation.
The additional IAC steps that are added for A/C on are "learned" within limits to smooth the A/C on transition.
The additional IAC steps that are added for A/C on are "learned" within limits to smooth the A/C on transition.
Team Owner
Joined: Oct 2006
Posts: 20,393
Likes: 431
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16-'17
NCM Member '09
I will tell you this, I recently had a custom PROM adapter made to slow my injector modulation down, and
a couple of other things (fans on earlier, and disable VATS), and it became a slow starter for a while, then
all of a sudden, boom, everything started working correctly. (I went to 24lb Motosport injectors)
a couple of other things (fans on earlier, and disable VATS), and it became a slow starter for a while, then
all of a sudden, boom, everything started working correctly. (I went to 24lb Motosport injectors)
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
The truth of it is, there is a little man inside your ecu. He has a flashlight and a note pad and takes notes covering all driving conditions. After a while, he will learn everything about your driving habits...hence the term ecu learning. 
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