280zx dies while driving, restarts by shaking ignition switch

[nickg]

Thought the topic would grab some attention.

I've got a 1981 280zx non-turbo, auto tranny, with about 124k miles on it.

So for about 3 years now, the car would randomly shut off while I was driving. Didn't matter how fast I was going, what the temperature outside was, the time of day, how much fuel I had, what day of the week it was, what mood I was in...

The solution was to just turn it over again and it would start right back up. Usually, I could be doing 70 on the freeway, and it could die, I could put it in neutral and coast while I restarted it. Or I could be sitting at a stoplight and the same thing would happen.

Over time, it got progressively worse. It wouldn't immediately start back up, it might take a few tries. Eventually it got to the point where sometimes I couldn't start it back up. I got it towed 3 times, and by the time I got it back to the house... the car would start fine. I could not figure it out... there was no consistency.

I replaced the ignition coil, the fuel pump, the fuel filter, spark plugs, spark plug wires, distributor, ignition switches. Nothing helped the problem. After doing all of this, and leaving the ignition switch dangling beneath the steering wheel while driving because I was in the middle of operations... I was driving along, and the car died. I lifted the ignition switch to put my key in to start it, and to my surprise, just by MOVING the switch, the car sprung back to life as if it had never shut off. So I drove around for a year like that... shaking my ignition switch whenever it would die while I was driving.

Now... it's worse. Not even that works anymore... immediately. I may have to sit at the side of the road shaking wires beneath my dash for 5-20 minutes hoping that some magic will fix it. And so far, it has... but I predict that the condition is getting worse and soon it won't.

Now... onto odd symptoms and things I've noticed.

• When the car dies, and I attempt to restart it, the starter motor works.
• There is no spark when it is in the "no-start" condition at the coil.
• The tachometer does not even jump when the starter is running (it does when it starts correctly.)
• I have run a wire directly from the BW wire at the ignition switch to the coil, thinking there was a discontinuity in the harness. Did not work.

My current theory after running across an unrelated post: the tach might be damaged and is not completing the circuit to the ignition coil... or a wire could be loose.

Help? Please?

[zbane]

I think you have the answer at your fingertips, literally.
When you state you have replaced the ignition switches, do you mean that you replaced the tumbler unit where you insert the key, or the wiring harness that attaches to it?
My guess is that it is the wiring unit that has failed-the actual ignition switch. If possible, check the contacts on the unit, and check the tumbler assembly.

As to your thought that your issues are related to the tachometer- Our ZX models will operate just fine without having an operating tach. For that matter, we can drive our cars without the entire dash assembly-no instrument cluster at all (I speak from experience)

[nickg]

that breaks my heart. I removed the entire dash today to check all the connections, and they all *looked* fine.

and I've replaced the actual switch itself, not the tumbler, a total of 3 times to no avail. In addition to that, I've replaced the actual plastic harness with another one, thinking that the contacts were somehow intrinsically flawed. I didn't actually replace the entire wiring harness, I just spliced a new connector on. I have this image of the wiring diagram for the 81 280zx from the factory service manual (which suggests that the tach is actually quite pivotal?). It's attached.

So if neither of these things are the problem.... what else could it be?

[nickg]

Also, does someone know where the ground for the tachometer physically grounds out? I'd like to check that... thinking it could be loose (assuming the tach actually has anything to do with this...) It's the blue wire out of the green harness from the dash (according to the wiring diagram above)

[nickg]

and confirmed... the car starts with no dash...

[nickg]

No one has any ideas? I plotted the wiring diagrams at work (2 sheets 2ft x 6ft) so I guess i'll be working my way through those today. The main issue here is no spark at the coil, probably due to a loose wire beneath the drivers side dash.

[Nigel1943]

No one has any ideas? I plotted the wiring diagrams at work (2 sheets 2ft x 6ft) so I guess i'll be working my way through those today. The main issue here is no spark at the coil, probably due to a loose wire beneath the drivers side dash.

Could be a fault on the auto box inhibitor switch.

[pit crew guy]

I had the same problem with my 2002 Dodge van the dealership found that my ECU (brain box) was causing the problem and replaced it at no charge. It has been fine every since then.

[sblake01]

I like Nigel's solution a little better. Calling the ECU on a 280Z/ZX a 'brain box' or comparing it to anything on a 2002 vehicle is like calling a 1970s transistor radio a home theater. The inhibitor switch and inhibitor relay seems to play a prominent role in the start/run circuit:

[nickg]

Where is the inhibitor relay at physically? is it the one attached to the air vent beneath the driver's side dash? And is the ignition relay up in the relay box in the engine bay?

[sblake01]

That I don't know because I'm not familiar with ZX's. I could tell you where the inhibitor relay would be in my Z if it had one (it doesn't-not an AT) but that probably wouldn't help you. I'll defer to David on that. Here's a link to an 81 FSM if you don't have one:
http://www.xenons130.com/files/1981%20280zx%20FSM.zip

[nickg]

Yeah, I've got the FSM, but it's nearly impossible to tell where it's actually located according to the diagrams.

[Nigel1943]

Yeah, I've got the FSM, but it's nearly impossible to tell where it's actually located according to the diagrams.

In the engine bay, passenger side, group of three, one nearest the front of the car.
There is also another ignition relay under the dash,passenger side, high level, second one in towards the front.

[nickg]

if the inhibitor switch or relay were bad, why would the starter motor even turn?

[Nigel1943]

if the inhibitor switch or relay were bad, why would the starter motor even turn?

The inhibitor switch circuit appears to not only have an effect on the starter but also the ignition.

[nickg]

It appears to only have an effect on the starter motor, actually. The inhibitor relay is activated when the ignition switch is in the IG position, and I believe the inhibitor switch is the one that prevents the starter from turning when the shifter is not in park or neutral. The ignition relay is also triggered simultaneously... but it does not appear that the inhibitor relay or switch does anything to affect the actual coil. I just mulled over the wiring diagrams for an hour and I'm fairly confident in that.

[nickg]

It seems that it was the ignition module. I replaced it and haven't had a problem in several days.