Sudden engine shutoff

[chaseincats]

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?

[Zed Head]

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.

[chaseincats]

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?

[Zed Head]

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.

[chaseincats]

I opened my ECU and I don't see any cold solder joints or anything

[Dave WM]

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.

[Captain Obvious]

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.

[240zadmire]

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 

[240zadmire]

After relighted the negative post, low/high lights magically come back to live and work again.  No need to replace anything. 😉

[chaseincats]

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.'

[chaseincats]

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.

[chaseincats]

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.