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Diagnostic Now....Broke XJ shaft, melted rotor. Cause?

snuffy74 said:
With a bad pickup coil, you'd still have spark when the truck is cold, but as soon as the pickup coil gets hot enough it shuts down and then won't run again until after the pickup cools down again.

Since you said your Suburban ran until after you swapped in a new distributor, I'd be willing to bet that it has something to do with that distributor. Like people have said here, 'just because it's new doesn't mean it's good'.
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Fair, but it worked fine with the new distributor....for about a day.

I'd think that with a bad pickup, it would still start at some point.....

BUt who knows.
 
Once solid state got well established, the rule of thumb became that if it survived 90 days of use, it was good for years if not decades unless mistreated.

Well over 95% of solid state failures occur in the first 90, and most of them in the first 10 to 20 days.

Unless it included damage replacement, I have not bought a warranty over 90 days for electronics equipment in 20 years.

And there is no reason for either the module or the pickup coil to fail completely. Either one could fail intermittently, or start false triggering.

A skipped tooth might be hard to spot, but I would think if you got the timing mark right on the indicator, you would be able to see enough offset of the distributor rotor to notice.
 
Situations like this kill me that not everyone on here is right down the road for me to go lend a helping hand!
 
y5mgisi said:
Situations like this kill me that not everyone on here is right down the road for me to go lend a helping hand!
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Thanks man. I'll get it figured out. I just hate diagnostics that are tedious.

Need to check chain slack, and compression tonight. Just hate pulling the plugs on this thing, now that it has headers.

Gotta keep my head down and follow the correct diagnostic procedures...although i want to drop the pan and just take a look at this damn timing chain straight up, and see if its stretched.
 
TIP: to see how slacked out the chain is quite easily, remove the cap off the distributor, rotate the engine clockwise and watch the rotor spin. Now, rotate the engine slowly counter clockwise. If the rotor does not immediately start rotating the opposite direction, there is slack in the chain. How long it takes for the distributor to "catch up" with the counterclockwise rotation is an indicator of just how slack the chain really is.
 
Also, this isnt the best pic, but if you'll notice, it would still be very difficult to see the timing chain with the oil pan dropped. The lower lip of the timing cover blocks the view pretty
 
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Maybe a better pic?

ST-1105-Build-43.jpg
 
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y5mgisi said:
Sorry about the big pics! Google not being kind to me.
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Understood.

That is the exact direction on diagnosis i have waiting in my PM box from Scott. That is what i am going to do tonight.

And, once i had the pan dropped....i was for sure going to remove the timing cover to inspect.
 
Ok, got the plugs pulled, and tried to turn the motor over backwards.

Crank pulley loosened...

So i used the alternator bolt, and was able to turn it forward / backward.

There was next to no slack in the timing chain, and the rotor moved almost immediately when i turned the motor.

I didn't get a chance to check compression.

Is there a possibility something in that "new" distributor died, and is allowing me to get spark / fuel.....without starting?
 
Is there a possibility something in that "new" distributor died, and is allowing me to get spark / fuel.....without starting?
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Yep.
 
4X4HIGH said:
Would love to hear this. If he has spark AND fuel there isn't anything in the dizzy that could be bad.
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Definitely have fuel AND spark. Timing seemed way off when i was cranking it, but wasnt' sure that was accurate.

Unless the distributor turned, or the gear spun....i have no idea how the timing would have changed. Hence why i've been hesitant to try and adjust it. But will as soon as i check compression tomorrow.
 
Well then that could be good news! Im guessing you had to turn in your old dist for a core? Either way, im just as curious as hell for that compression test and when/if you end up pulling the distributer or attempting to re-time it and see what the results are! Only thing i can think of is possibly the pick up in the distributer was never tightened down right in mexi... i mean, the factory and possibly it turned inside the dist? Dont know if thats even possible. Also, with the type of rotor you have i have heard (never seen in person) that the rotor can strip its littl plastic "tooth" that keys it to the shaft and can spin on the shaft. The biggest thing that keeps sticking in my mind is at one point you said you were tryin to start it, with the timing light hooked up, and the mark was nowhere to be seen. So it SEEMS to me that the timing is out of whack for one reason or another. The compression test will tell alot about if there is any kind of internal issue. Then, i would guess it best to give a quick shot at just re timing it like normal and go from there. Just killing me not knowing what the problem is!
 
4X4HIGH said:
Would love to hear this. If he has spark AND fuel there isn't anything in the dizzy that could be bad.
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I assume we are still dealing with electronics here. If it were points, I don't see a way to have both.
But, with that module involved, the sky is the limit.
I don't have a schematic or even a operating flowchart. But it has to work something like this:

The pickup coil generates a signal when the reluctor passes it. Couple of ways it could do that, and a couple of types of signal that it could output.
Doesn't matter.
The ignition module receives that signal. At this point, a defective coil could send in a noisy signal, or noise could get onto the line.
Assuming that that is OK, then the module has to amplify the signal, possibly modify it, and send it out.

At this point you have active components involved. Transistors, maybe Schotty diodes, triacs, darlington amplifiers, etc.
Any of these can go into oscillation and start generating a signal at the wrong time, or even when no trigger exists.
You could have one trigger when the dist. is supposed to fire, and get a dozen out. Or they could be delayed.
That module probably is supposed to fire on either the leading or trailing edge of the more or less square wave pulse from the pickup coil.

If the signal is weak, then it might fall into the "don't care" region of the module. A signal at that level is not guaranteed to either fire or not fire. And might do either one.

Just something as simple as a broken wire in the pickup coil, could make and break a couple of times per pulse, and send multiple pulses to the module.

Any of the possibilities would supply pulses to the controller telling it to pulse the fuel injectors plus to the coil to fire it.
But they would be either at the wrong time, or have pulses in between the good ones.

Is that what is happening? No idea. But, he put on a new dist. and the engine quit working shortly thereafter.

I would suspect a mechanical failure before the electronic one, but either one is possible.

I saw one of the old Ford Duraspark modules go nuts one time. It went into some kind of internal oscillation. If you just turned on the key, it would get hot, and whichever plug wire the rotor was pointing at would continuously fire without the engine turning over.

Never underestimate the weirdness of electronics........
 
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