Yeah, that's exactly what I thought, LOL, "special race tool." That's what the guy said who called me back after initially calling to say the part didn't fit and was (the incorrect fitment) allegedly confirmed by measurements taken by the tech. I was expecting to have to argue over an inflated bill as a result of the time he seemingly spent trying to figure out how to install an aftermarket distributor that he wanted to believe just wouldn't interchange with the stock unit. Fortunately he didn't charge me for his learning experience.

Are you saying then that if I adjust the camshaft sensor offset by a degree or so that I won't need a crank relearn, that the PCM only ever needs to learn it once??? (I still haven't checked the current cam sensor offset, but will later today.)

After a crank position sensor replacement, for example, that would be a case where a relearn would need done, right? I guess I'm not sure what the crank relearn literally entails. From your earlier post, I gather the PCM learns the recognition of the crank sensor's magnetic signature. But how that actually takes place and how that information is precisely used, I'm not sure. Part of what is confusing is that I don't understand why the procedure has to be specially initiated and can't be done automatically, especially if the vehicle is already running properly. Seems to me, the PCM could simply get a reading from the sensor at whatever point in the crank rotation and then compare that with other parameters to calibrate exactly where the crank is at a given point (as well as learn any offset-correction of the crank sensor signal), regardless of subtle variances between sensors. (Basically, I'm suggesting that the PCM hypothetically could regularly calibrate itself instead of needing a special relearn to be initiated by a tech -- if GM had designed it that way.) But as that is not the case, the learned data must therefore be somewhat volatile between relearns, and so I wonder what adjustments would interfere with this learned data, thereby necessitating another relearn. In contrast with the preceding paragraph, why was the relearn necessary when replacing the distributor whereas you say the PCM only ever needs to complete the process once per engine? I think I am getting it, but some information seems conflicting. Earlier I read that rotating the engine without the PCM (as in the case of cranking the engine with a new/different PCM), then putting the PCM back in would necessitate a relearn (suggesting high calibration volatility), but now I am lead to believe the PCM only once needs to learn the crank position and is good to forever on that engine (suggesting very low volatility). Please forgive me if I am forgetting something.

The ECU (electronic control unit), ECM, or, specifically, the PCM, as you mentioned, I believe I am curious how the BCM interacts with it. First of all, where is the BCM located, and is the Passlock incorporated therein? Secondly, are you saying the BCM stores the VIN from the PCM independently in order to prevent a new PCM from being installed? If so, I suppose it only safeguards the VIN and no other such parameters, only unless a new VIN is supplanted through the Passlock disable procedure posted earlier by bromanjr?

When guys casually talk about buying a flashed PCM or having their PCM flashed, I doubt they all go through performing a crank relearn (since no one seems to have easy access to the tool). I also flash my PCM from time to time. I suppose that somehow flashing the PCM ROM does not interfere with learned crank data (or maybe not enough to notice a difference), in which case only the guys with a new PCM that have their correct VIN flashed would need a relearn (because although the BCM would accept the VIN from the PCM, the PCM would not have the accurate crank position data). So my question here is, getting back closer to the thread topic (I know people on here seem to get irritated if topics wander too much):

1) Can/will flashing my PCM interfere with learned crank data?
2) If it will only interfere if I modify specific values, what values/tables comprise the learned data?

One reason I ask is because I can back up the current PCM data, but if I flash the PCM with a copy of the data it had when it went into the dealer, would it lose whatever data was collected during the crank relearn?

Thanks so much for helping me understand this all.

 

Camshaft retard is a physical adjustment that you do by turning the distributor. It aligns the camshaft position sensor with the camshaft so the PCM "knows" exactly where the camshaft is in its rotation. Once it is adjusted correctly, it will not change unless the distributor hold down is loosened and the distributor is moved. Replacing the PCM does not affect camshaft retard.

The crankshaft position sensor relearn is done electronically inside the PCM. During the relearn the PCM "learns" where the magnetic field is directed in relation to the tone ring on the crankshaft. The relearn "shows" the PCM exactly where the crankshaft is in its rotation. If the crankshaft position sensor, or the timing cover are disturbed in any way, the PCM needs to relearn the sensor again. All calculations and adjustments that the PCM makes are based on crankshaft position, it must be accurate.

Correct.

There are only two things that require the relearn to be performed: 1) The sensor and or timing cover have been disturbed, or 2) The PCM is replaced with a different one. If either of those two conditions occur, I can assure you the engine is NOT running properly, no matter how well you think it is. The relearn must be initiated by a scan tool to prepare the PCM to change the current relearn data that is stored in the PCM.

Not if you put the original PCM back in.

Again, there are only two things that require the relearn to be performed: 1) The sensor and or timing cover have been disturbed, or 2) The PCM is replaced with a different one.

The BCM is located under the dash, just left of the ash tray. The BCM controls body related items such as instrument cluster, interior and exterior lighting, power locks, Passlock, horn, etc etc. The BCM is not vehicle specific as those functions are the same on each S&T body vehicle for a given model year. Here's an example of the various modules sharing data: When the PCM runs the monitor for the EVAP system, fuel level data is necessary. The PCM gets the data from the BCM via classII serial communications. If the level sender is not supplying data to the BCM, the EVAP monitor will not complete its tests.

It depends what values are modified, and how the programmer modifies them.