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Sudden engine shutoff


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Really strange thing happened today.

I was sitting at a stoplight idling and the car suddenly died.  The car runs so smoothly that I didn't even know it was off until I looked at the gauge and saw the e-brake light on.  I turned the key and it fired right back up like nothing happened and drove home another 20 miles without issue.

This is probably electrical/spark related since if it was fuel the car would have stumbled before it shut off I'd assume.  I popped the hood when I got back to see if anything was loose then checked under the dist cap to see if the pickup coil was chewed up at all and everything looks perfect.

 

Any ideas where to start?

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I had a 1978 ECU that did that when I was testing it.  Died and restarted a couple more times then I had to jog home and get the original to put back in.  Ignition modules do that too.  Carry spares.

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13 minutes ago, Zed Head said:

I had a 1978 ECU that did that when I was testing it.  Died and restarted a couple more times then I had to jog home and get the original to put back in.  Ignition modules do that too.  Carry spares.

Is there a way to test the ecu to see what the issue is?  Do you mean the big 'transistor ignition module' box in the passenger footwell?

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Not if it's just crapping out then coming back to life. 

And yes, the big box.  They fail in different ways, but dying then coming back to life is one of them.

Old "new concept" electronics.  1975 was the first EFI 280Z.

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If you really wanted to test it, I would think it would prob have to happen very regularly, Have it opened up like above, have a test stand, and while the engine is running you could try thermal shocking it with some dust off to see if you could find a place on the PCB that reacts.

Something to consider would be an ign switch. I have had trouble with mine on start up, I presume trouble could happen while running for the same reason, intermittent connections. It a mechanical device, making is subject to wear from use. As cheap insurance if the problem repeats you may want to replace it. Its cheap (40$ get the nissan OE one) and easy. I carry several spare ECU's and ign modules have tested them all to be sure they work.

While on the topic, you should go thru your wire harness and make sure all connections looks good, grounds and pins.

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12 hours ago, chaseincats said:

Any ideas where to start?

I would start by watching for the situation to occur again and try to get a feel for what's going on. I think all this poking around with the ECU as a culprit is premature.

My car would sometimes shut off when I pulled up to a stop. Engines don't like a rapid drop from load to idle. It's just unstable. Modern engines running a fast control loop use technology and speed of response to take care of it, but back in the old days, it was never uncommon to pull up to a stop sign and sometimes have your car stall. If your car was tuned properly and running good, it was "rare", but it did happen.

I think mine was caused by a rich fuel mixture, a BCDD that was disabled, and an idle that was set a few RPM lower than spec.

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This issue happened to my 280z ‘77 once.  Engine died at stoplight but fire up immediately.  I didn’t pay much attention back then.  Thought it was just a rare one off occurrence.  Weeks later as I haven’t drive the car for at least 4 weeks, I couldn’t start the car at all.  No ignition engage, no clicking of the starter … spends hours troubleshoot.  Battery was good….  Cabin lights turn on…. Head lamp works for high beams but not low beams.   I’ve been driving with high beams for weeks thought that the headlamps are on its way out… just haven’t got time to get around to replace them as I don’t drive at night that often… long story short, when I couldn’t start the car at all and spent hours troubleshoot… turn out the negative battery post wasn’t firmly tighten.  I guess when starting the engine, starter draws strong current and if it is not firmly connected, it won’t turn over though other lights draw less current work fine.

I’m sharing my experience hopping yours is as simple as mine and won’t need to replace a lot of component.

I have been driving the car for months now almost daily at least 10 miles each day.  Enjoying it a lot 

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1 hour ago, Dave WM said:

If you really wanted to test it, I would think it would prob have to happen very regularly, Have it opened up like above, have a test stand, and while the engine is running you could try thermal shocking it with some dust off to see if you could find a place on the PCB that reacts.

Something to consider would be an ign switch. I have had trouble with mine on start up, I presume trouble could happen while running for the same reason, intermittent connections. It a mechanical device, making is subject to wear from use. As cheap insurance if the problem repeats you may want to replace it. Its cheap (40$ get the nissan OE one) and easy. I carry several spare ECU's and ign modules have tested them all to be sure they work.

While on the topic, you should go thru your wire harness and make sure all connections looks good, grounds and pins.

That makes sense but may be tough to put the engine on a stand.  I replaced the ignition switch in 2017 due to it not firing during cranking so it shouldn't be that.

Regarding the connections, I went through the AtlanticZ connection cleaning page (http://www.atlanticz.ca/zclub/techtips/electricalconnections/index.html) a year or so ago and everything is now 'like new.'

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34 minutes ago, Captain Obvious said:

I would start by watching for the situation to occur again and try to get a feel for what's going on. I think all this poking around with the ECU as a culprit is premature.

My car would sometimes shut off when I pulled up to a stop. Engines don't like a rapid drop from load to idle. It's just unstable. Modern engines running a fast control loop use technology and speed of response to take care of it, but back in the old days, it was never uncommon to pull up to a stop sign and sometimes have your car stall. If your car was tuned properly and running good, it was "rare", but it did happen.

I think mine was caused by a rich fuel mixture, a BCDD that was disabled, and an idle that was set a few RPM lower than spec.

That makes sense but the strange part was that 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.

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19 minutes ago, 240zadmire said:

This issue happened to my 280z ‘77 once.  Engine died at stoplight but fire up immediately.  I didn’t pay much attention back then.  Thought it was just a rare one off occurrence.  Weeks later as I haven’t drive the car for at least 4 weeks, I couldn’t start the car at all.  No ignition engage, no clicking of the starter … spends hours troubleshoot.  Battery was good….  Cabin lights turn on…. Head lamp works for high beams but not low beams.   I’ve been driving with high beams for weeks thought that the headlamps are on its way out… just haven’t got time to get around to replace them as I don’t drive at night that often… long story short, when I couldn’t start the car at all and spent hours troubleshoot… turn out the negative battery post wasn’t firmly tighten.  I guess when starting the engine, starter draws strong current and if it is not firmly connected, it won’t turn over though other lights draw less current work fine.

I’m sharing my experience hopping yours is as simple as mine and won’t need to replace a lot of component.

I have been driving the car for months now almost daily at least 10 miles each day.  Enjoying it a lot 

I will say I did not have the negative terminal REALLY cranked down as I was taking it on and off when working on it.  When I got home I popped the hood to look and the terminal was on there.  Before I removed the ECU I pulled the terminal off and it required some strength to do so but I still could.  The terminal and connector are in great condition.

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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.

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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?

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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.

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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.

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Posted (edited)

@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.

unnamed.jpg

Edited by chaseincats
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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. 

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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.

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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.

unnamed (1).jpg

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  • 2 weeks later...
Posted (edited)

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 by chaseincats
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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.

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10 hours ago, Captain Obvious said:

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.

I just went to test it and got 740 ohms.  The FSM says it's bad if it is "far less than, or more than, 720 ohm" so I guess that at least on paper isn't it.

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