Sudden engine shutoff

[Jarvo2]

I had to replace the ignition switch (behind the key) on the steering column as my 45+ year old one in my '72 seemed to have crapped out while cruising down the highway due to the bouncing of the keys against the ignition switch.

[chaseincats]

1 hour ago, Jarvo2 said:

I had to replace the ignition switch (behind the key) on the steering column as my 45+ year old one in my '72 seemed to have crapped out while cruising down the highway due to the bouncing of the keys against the ignition switch.

The car will shut off while running if the ignition switch is faulty?

[Captain Obvious]

On 7/9/2021 at 10:22 AM, chaseincats said:

it wasn't right when I came to a stop, I was idling at a red light for a good minute or more before it died.

Oh, then forget about what I said about coming down off load to idle. That's not it.

You had mentioned earlier that you thought it would be ignition related since it didn't stumble before it shut off. In my experience, there isn't any significant stumbling when the fuel pump shuts off. It just dies.

So how about this (since you have a 78)... Your oil pressure drooped enough in your hot idling engine and opened up the fuel pump switch and shut off the fuel pump? Or the "L" terminal on your alternator is acting up at low RPM's. That could also shut off the fuel pump.

[Zed Head]

You have now entered the gauge hyper-awareness zone.  Watch those needles.  Try to remember exactly what they were doing just before it dies again.

[siteunseen]

BCDD is what I'm leaning to.

Does the tach get erratic during these episodes?

[siteunseen]

Old stand by question for everything but how do the plugs look? Is it no spark or no fuel?

[chaseincats]

@Captain Obvious In my experience when the pump dies the car stumbles a bit before the car dies as it burns through what's left in the rail before finally dying instead of it just all dying at once - at least that's how my car handles a fuel pump cutoff?

@Zed Head I remember looking at the needles while sitting at the light before it shut off and everything looked great which was odd.  I was being paranoid about the gauges since it was pretty warm out and was checking them habitually.

@siteunseen The car doesn't have a BCDD anymore and I don't believe the tach needle was freaking out.

 

I took the ecu and transistor ignition box apart and neither had any visible issues like burns/loose solder joints/etc.  I then looked around through the ignition system via the wiring diagram and the only thing I could find was a mysterious burn on the distributor's pickup coil's wire bundle shielding (see below image).  It looks almost like a spark arched out of it or something because you can see the red wire in the bundle as the outside protective wrap was melted through (the wire's insulation itself didn't look burned).  If that's the case, then that spark arching to the engine would have shut it off.  I don't understand how that could have happened though...

That distributor was installed (not refurbished) about a year ago and that burn wasn't there otherwise I'd have sealed it with electrical tape or something prior to installing it.  I'm not sure how long the wire has been like that or if that is indeed what happened though.

Is my theory plausible?

Note: the casing in this picture looks ripped/torn but that is just a bad picture its very much melted around the areas where the holes are.

Edited July 11, 2021 by chaseincats

[Captain Obvious]

If the signal from the distributor pickup (the red and green wires) gets interrupted, the engine will shut off. No question.

So "plausible"? Absolutely. However, if the insulation on the wires inside that outer protective jacket is still intact, then I might question the probability. But certainly plausible.

I'm trying to come up with something that may be likely to "act up" when sitting still at a traffic light with the engine at idle. I'm not sure an interruption in that signal would be any more or less likely to occur under those conditions. 

[Zed Head]

How about a neutrino?

When I had that bad ECU it died immediately.  So that would have been loss of injection.  I've also had a failing EFI relay that almost stranded me, but that was a restart of a hot engine problem, not a dying while running problem.  Many old electronic parts that might have a momentary failure.

I think that the red and green wires have low voltage at low RPM.  Probably no real "jumping" ability, you'd need contact with a ground.  Have you examined the wires around the breaker plate?  One thing that is unique to the idle condition is that the breaker plate is at its lowest advance state.  The red and green wires do get worked a bit as the plate rotates in relation to where they leave the distributor body.  People have reported problems there.  Unusual though.

[chaseincats]

6 minutes ago, Zed Head said:

How about a neutrino?

When I had that bad ECU it died immediately.  So that would have been loss of injection.  I've also had a failing EFI relay that almost stranded me, but that was a restart of a hot engine problem, not a dying while running problem.  Many old electronic parts that might have a momentary failure.

I think that the red and green wires have low voltage at low RPM.  Probably no real "jumping" ability, you'd need contact with a ground.  Have you examined the wires around the breaker plate?  One thing that is unique to the idle condition is that the breaker plate is at its lowest advance state.  The red and green wires do get worked a bit as the plate rotates in relation to where they leave the distributor body.  People have reported problems there.  Unusual though.

The wires inside look good but the ones outside look a little cooked.  That said, it's been like that since I got it and it runs great after the restart and now.

[chaseincats]

Update:

For a while (I don't remember how long) you could smell hot electricals on the drivers side of the engine bay when the car was running but without visible smoke or poor engine performance I ignored it (I know that was dumb).  I noticed after the issue we've been talking about and taping up that burned pickup coil harness cover, that smell is now gone.

Could a pickup coil wire build up resistance somehow and is there a way to check it?  The car runs fantastically so I didn't think that could have been the case until I noticed the smell was gone last night for the first time in forever.

Edited July 22, 2021 by chaseincats

[Captain Obvious]

You can certainly measure the resistance of the pickup coil. I assume (but haven't looked) that there is a spec in the FSM to compare it against.

But I'm thinking that if there is enough heat up there to cook the insulation on the wires, that just wrapping them with tape wouldn't change much. You would just start cooking the tape instead of cooking the wires.

Bottom line? I think it might be a red herring, but I'd keep a close eye (and nose) on it. There should never be a hot electronics smell in the engine compartment. I know exactly the smell you're talking about, and that should not be happening.