My point is, why would you want to even try...? And why are we even discussing this...LOL

Get the distributor a few degrees off and the thing won't run anyway, regardless of the timing. Ever done a cam swap?

 

Are you even reading what I'm saying? Here, try again:

"That's where your problem is...You can't move the distributor without killing the fuel sync, so why would you?"

And your problem lies in the fact that you somehow think I'm advocating this. Did you read this entire thread, or are you just hell-bent on being combative?

If you do read it in its entirety, you might see where I'm coming from, and why I find much of what you're saying extremely annoying.

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And the annoyance continues. "Why are we even discussing this, LOL?" I'm discussing it for a variety of reasons, one of which is to gain a deeper understanding of how our engine management system works, and none of which are any of your business.

 

Moving the distributor housing only affects the fuel sync because the pcm only sends spark when the crankshaft sensor hits a window in the flexplate, signifying the piston is near tdc on a compression stroke. Data from the various other sensors factor in the amount of advance can be had.

Twisting the distributor past +/- 20 kills the entire truck as the sync between the cam and crank sensors is out of spec from what the pcm wants to see, and the pcm forces a shutdown, or no start condition. This is not a great enough distance to cause the spark to jump to the next pole under the distributor cap. It doesn't matter if the spark happens at the beginning of the rotor and terminal touching, or the end of them touching, the spark will still transfer.

 

We've been over this. The crank sensor cannot determine which cylinder is which because it has no missing teeth nor can it tell if it's the compression stroke or exhaust stroke because it takes 2 revs of the crank to fire all the cylinders. It needs the help of the cam sensor, the cam sensor tells the PCM which cylinders in the firing order are up next, then the pulse from the crank sensor fires the coil as it sees the notches in the flywheel (and can vary the timing of course).


It doesn't change timing because the coil is fired from the crank sensor, the spark will jump from the rotor to the cap over a large swath of degrees, the cap/rotor is only a means of delivering a spark to the correct cylinder. In a "normal" dizzy, the trigger (points, hall trigger, ect) is what is moved (just as if you adjusted the crank sensor on a Magnum) and that it what changes timing, not the cap/rotor relationship.

 

Thanks Hahns, that was the best explanation yet, and clears up a misconception that I hadn't quite got past about how the spark can still get from the rotor to the contact inside the cap in a "timely" fashion, even if the distributor has been moved a little. Not at all like my International 392.

Still one thing I don't fully understand: how the PCM keeps track of exactly which injector to fire, and how it never loses track no matter what the engine is going through.

Spark, easy to figure. Crank and distributor are always linked, PCM knows "a" cylinder needs a spark, distributor gets it to the right one.

So, how does the PCM never "forget" which injector needs to fire next? It seems as it if would have to be getting a signal telling it when cylinder 1 is at TDC, or some other reference signal like that.

 

So does anyone have any ideas why when i replaced my cap and rotor, did the plenum, and new intake gaskets, my truck takes 10 times more cranking to fire up? Prior to all this, the truck started first rotation, EVERY time. Now it just cranks and cranks and cranks. sometimes I pump the pedal, but i doubt this is actually doing anything to help. when running, the truck runs better then before, but its a pain to start. Ideas?

Edit: John D, I have taken your advice.

 

My best guess on how the pcm knows the correct firing order of injectors lies in the cam sensor. The pcm sees a disruption of the hall effect and knows that at a specific time after the disruption is registered, fire injector number x.

 

I still don't see how the PCM can always remember which injector to fire, even after the CMP has been removed and replaced, for example. Or if the engine has been physically moved with the engine off, especially with a manual transmission. You park on a hill, put it in gear, and it rolls a little. How does the PCM never lose track of which cylinder is which?

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2x1972, I think you should put that in a new thread.

 

See if this helps answer your Q's

http://www.noid.org/~lj/PCM%20Tutorial/PCMtutorial.htm

 

I Did you turn the distributor even a small amount?