Z dies after warmed up 77 Z Drives For About 10 To 15 Minutes,then Dies.

[Crazy477280Z]

I will try your tips tomorrow.O Reillys is going to test module though how they can tell its bad when it doesnt begin to fail until after it heats up. Zed Head,did you mean ground wire coming from tach? I wouldnt think you would ground resistor,right?

[Zed Head]

I would check the ground wire for the tach first.  If the tach is losing ground it would be like disconnecting the tach.

 

If everything looks right though, and you want to try running it without the tachometer, in case the tach is causing the problem, then try grounding the resistor.

 

The fact that you still have spark but the tach stops working seems to show that you're losing that path to ground.  Either because the circuit is broken inside the tach, or because the tachometer's ground wire is bad.  And I know that the EFI engine won't start without the tach.  It might cough a few times from some cold start valve fuel but won't run.  

 

I had the resistor fall out on my car once and the engine didn't even pop, but I don't have a CSV.  I put the resistor back in and it fired right up.  I've repeated the experiment, on purpose, since then.  Some people don't believe it, but it's easy to test.  Pop the resistor out - no start.  Replace - back to normal.

 

Anyway, that's just some background  Keep looking at diagrams and testing parts and something will crop up.  I know someone who had a corroded fuse that would overheat just from current flow, causing everything to shut off.  Sit for a few minutes and it would start right back up.  That was a BMW though.

[Captain Obvious]

I took a look at the wiring diagrams and I can't provide any input as to if/why the fuel injection would work properly or not if there was something wrong with the tach or it's series plug-in resistor.

 

I can tell you, however, that it looks like the ignition and fuel injection sections should work just fine even if you were to pull that resistor out of the circuit or if the tach were completely removed from the dash. Not saying it really works that way, but looking at the diagrams, that's how it SHOULD work.

 

I also can tell you that the diagrams don't do an accurate job of showing what's inside the tach. I know there are artists liberties taken at that level of detail, but if the internals of the tach were constructed as shown, it simply wouldn't work. Doesn't matter for this discussion though.

 

So I don't remember if I have a tach laying loose or not, but if I do, I'll take a look inside and see if I can add anything to the discussion. I've never been inside a tach before. They've always just worked for me.

 

Also, Zed Head, you mentioned that the wiring diagram shows a dedicated ground wire through C1 for the tach. I know it looks that way on the page you referenced, but that's just Datsun's way of simplifying the sub-system being highlighted. The tach has no dedicated ground as that same ground goes lots of places. Datsun's thought is that when you are interested in the sub-system (tach in this instance) that you don't care about or need to know about where else those wires connect to. So they "simplify" the sub-system diagram accordingly and don't show all the other places the connections go. If you want to see where else a wire goes, you have to refer to the complete wiring diagram.

 

I've found that scheme a help or a hindrance. Helps when you're trying to figure out how a sub-system works, but it's a hindrance when you're trying to figure out "so where else does this wire go".

[Zed Head]

The possibility of a wiring diagram error did pop in it to my head last night (again, I think it's been in there before).  I might pop that resistor out and see if Pin #1 still has a path to the coil.  We might hit 70 degrees here today.  Weird weather.  If the resistor is inline with Pin 1, instead of branched, that would explain why no resistor caused no-run.  BUT, I discovered the phenomenon when I tried to move my car with the tachometer out.  Anyway, one of those puzzles  

 

"Ground by wire" would have been more descriptive.  My meaning was more that it doesn't depend on a ground through the mounting bolts, although it may also ground there.

 

It's been in the back of my head that it could just be an ECU problem.  But, the weird tach behavior is there.  I hope a clear answer and solution comes out, even if it's just localizing the issue to one component.  Nothing worse that a problem that disappears for no reason.

[Captain Obvious]

I took a look for a tach other than the one in my dash and came up dry so I can't add any additional details there.

 

Like you said... One of those puzzles. So yeah, if you get the opportunity and feel like experimenting it would be interesting to see what happens when you pull the tach resistor. My car is still laid up for the off season or I'd try it. C'mon Spring!

 

Maybe your car WAS running the last time you tried it, but since the tach read zero maybe you just didn't know it? What kind of exhaust you got?  ::

[Zed Head]

Nah, I know it wasn't running because I had just jumped back in after about an hour and a half and distinctly remember that feeling of "what broke this time" when it didn't start.  Then looking over to see the resistor laying on the passenger floor.  I had just done some work under the dash, putting in a relay for the lights, and the resistor was unwrapped because I had wanted to see what it looked like.  Months before that I had the tachometer out and wanted to move the car but it wouldn't start.  Reinstalled the tach and it started right up.  Also did the same thing on a 1978 parts car that had a running engine.  Used to start the engine every few weeks and it wouldn't start after I removed the tach.

 

BUT.  Someone else will have to test the factory stock system, which is what I used to have.  Because I went out this morning and the engine starts with or without the resistor.  So now I have to add a disclaimer whenever I talk about this.  One thing I had wondered about was the need for some transistor systems to have power to one side to lock in the logic state.  Maybe the stock system needed that and my GM HEI module doesn't.  Or it's more robust and needs less or can handle more.  While I had the resistor out, I measured both sides of the circuit, because if you look at the BE diagram, they draw a little square component with fused power to one side and the coil negative power on the other.  Both sides had battery voltage, even though the tach side can only get it through that little square.  this is all with the key On, engine not running.

 

That's all my spongiform electronics knowledge can come up with.  If I ever get another stock 280Z I'll probably test this again just to know, before I start modifying.

[Zed Head]

A thought on a possible diagnostic tool.  A spare tachometer or a meter with tachometer or frequency measuring ability attached to the coil, or the ignition module blue wire in the cabin (so you can see it easier) might tell if it's the tachometer failing or spark disappearing.  That's always the first split in the trouble trail - fuel or spark.  It would have to be visible so you can see immediately if you have spark when trying to restart or when it dies.

[240260280z]

If it continues to be electrical, it could be a condenser heating up and shorting. It happened to my 83 Tercel 4X4. Ignition module is the usual suspect but condensers can cause the same problem. You can simply disconnect them to test.

Debris in fuel tank can also cause the car to die.

[EuroDat]

Someone else will have to test the factory stock system, which is what I used to have.  Because I went out this morning and the engine starts with or without the resistor.  So now I have to add a disclaimer whenever I talk about this.  One thing I had wondered about was the need for some transistor systems to have power to one side to lock in the logic state.  Maybe the stock system needed that and my GM HEI module doesn't.  Or it's more robust and needs less or can handle more.

Mine is the same. It runs perfectly without the resistor installed. I don't know if it ran without it before I did the GM HEI module mod.

Not sure what to expect with a 280Z running aZX dizzy???

Chas

[Crazy477280Z]

Well, I switched over to GM HEI . Car ran for 10 seconds, then died. Still getting good spark at coil. I am still running the 81 zx coil,because I really havent researched what coil would be best to run with the stock GM module.So Ime going to start back at beginning starting with EFI tests, then tracing and troubleshooting every wire in ignition series. Ive been tempted to pull my matchbox dizzy and coil out of my running 81 zx,and installing them in 77 just to see what happens. I just dont want to needlessly burn something up, if there could be something causing this. I still might do it if I cant find a problem anywhere else. I will see what happens tomorrow and post what I find. Ime going to find out what coil will work the best. I just read your post on condensors also Blue, and will be sure to check them. I cleaned out fuel tank last summer and also run two fuel filters, but a good tip anyway. If anyone could give me a good coil choice to run with a 77 280z dizzy,GM HEI module....please throw a post my way...I thank you greatly!

Edited March 9, 2015 by Crazy477280Z

[rossiz]

just throwing this out there, but my '78 gave me lots of grief due to the efi relay - i was doing the classic shade-tree "wiggle test" to various connections and found that pressure on the wiring was causing the relay to flex and the connection wasn't being made internally. just a thought...

[Crazy477280Z]

I just replaced it when all this began. Then the coil, then converted to zx ignition with used E12-80 module,replaced that with new E12-80 module,now changed over to GM HEI ignition,,,,,and I still have same problem,only now it only runs for about 10 seconds. It will start up again after another 10 to 15 seconds.Ime going to start from square one again and see if I can figure this out. I will post my findings later, if anything new,butt what a pain in the rear area!!!