How does a CASE re-learn work?

[johnmaster]

In my ongoing series of questions asked that no-one should really ever need to know the answer to:) I ask, How does a CASE re-learn work? What is happening? The computer is calibrating the crank sensor to the reluctor ring to the way the block/crank were machined right? Then it adjusts it's setting and it knows how to properly time for spark and fuel events? But what is it using to calibrate the sensor to the crank/block? How does it know when it's right?

The reason I ask it that I am disabling and removing most of the sensors that the regular fuel system uses and I would hate to not be able to do a relearn due to poor planning.

Thank you for humoring me. Please point me in the right direction if you know where I can find some background on this.

[joecar]

The PCM measures the rate of deceleration of the crank and stores this information for reference/comparison during each power stroke if the conditions are correct (no bumpy road signal from ABS controller).

[ChipsByAl]

Then it adjusts it's setting and it knows how to properly time for spark and fuel events? This is incorrect, the CASE learn has nothing to with the spark or fuel delivery. It is used for misfire diagnostics. It is helpful for accurately locating a cylinder that has a misfire. If it isn't done on a PCM/ECM that has not been learned, the SES will remain illuminated till the procedure is done successfully. The CASE learn allows the PCM/ECM to sync with the unique combination of that engine's block, crankshaft, crankshaft sensor and balancer. If any of the prior components are replaced the CASE learn procedure should be performed again.

[swingtan]

+1

My understanding was that the procedure requires the engine RPM to be steadily increased through 4000 RPM. At this point the ECM deliberately miss-fires a cylinder and measures the drop on crankshaft speed. This value is then used as a factor to detect any other miss-fire event, as the ECM now knows what to expect. I'm not sure how much the other components are "directly" coupled to this, but anything that changes the load on the crankshaft would alter the setting.

Simon

[johnmaster]

Ahhh! I see says the grasshopper. I always wondered how it knew that a misfire occured. Thinking about it now, the Cam sensor must be controlling the spark and fuel timing because the crank wouldn't know which phase it would be working on. (right?)

So either way, it sounds like none of the other stuff I disabling could affect this relearn process.

[swingtan]

The cranks sensor and the cam sensor influence the fuel and timing. The cam sensor provides the "phase" as you put it, the crank sensor provides the fine calibration for timing.