'75 280Z - Starts and Runs, Shuts Off after 30-60 minutes

[zKars]

The engine bay does have that “post 75” look doesn’t it? If the head is an N47 rather than the expected N42 on a 75, then.... With the many years of history, who knows what parts have been substituted in. 

The only concern I have is the plastic fuel filter back by the tank, but only if its on the output side of the pump. If its between the tank and the pump inlet, it’s under no pressure (vacuum actually) and should be fine. If its there, then there has to be another proper high pressure EFI filter under the hood between the Body hard line from the tank and fuel rail at the front right of the engine.

Heat soak is rarely an issue with EFI engines. I’m leaning on the ignition module failure as the likely cause. Or coil, or distributor pickup heat related failure.

[Dave WM]

If you have spark while cranking and the engine does not start, then its likely a fuel issue,

Heat soak is a big issue, generally show up AFTER shutting off the car during hot days. I generally open the hood after I get to my location (or even just getting gas). Its a good time to look over the engine, check for leaks, check oil, etc...

With heat soak the engine will be difficult to start, a work around is to floor the gas pedal. this will cause the ECU to go into more fuel enrichment mode (assuming it all works correctly) and will help with the startup. This is actually stated in the owners manual. Other issues that cause odd flame outs is low fuel and hard left turns, at least in the 1975 versions. get it below 1/4 tank or less and a sharp turn will slosh the fuel enough to starve the pump, does on mine anyway.

Assuming its not heat soak (again this would not be a cause while the engine is running as cold fuel is constantly running thru the rail), you need to diagnose the fuel system. New plugs should not turn black, if they do its rich, could be temp sensor,cold start, ECU, fuel pressure, TPS, the FSM covers this.

If its choking out (thick black smoke) after warming up the temp sensor should be checked AT THE ECU connector per the FSM.

If it will not restart and you have spark you should next look for injector operation. a noid light or just a long stick touching the injector while you listen to the other end (mech stethoscope is the best way, cheap at HF) you should hear clicking noises while cranking. If not clicking the injectors are not working. possible ECU or wiring from coil to ECU or some other fail.

a neat tool is those inline spark checkers, just a neon flash to confirm spark energy is getting to the top of the plug. easier to use than the spare plug routine.

 

[Zed Head]

8 hours ago, zKars said:

Heat soak is rarely an issue with EFI engines. I’m leaning on the ignition module failure as the likely cause. Or coil, or distributor pickup heat related failure.

Actually, heat soak has been a big problem with the 280Z's.  We've had some good discussions about it in the past.  Although, it's possible that the fuel blends have changed over the last few years and it's not as bad now.

[Zed Head]

20 hours ago, Bigz Zee said:

Is there Water Temperature Switch on this car? Isn't supposed to be on the side?

Looks like there are three sensors on the front.

Should have a thermotime switch, with an injector-type plug, and a coolant temperature sensor, also with an injector-type plug, and a temperature sender, with a single wire attachment.  Later cars have a fourth switch, for the vacuum advance solenoid.

[zclocks]

Zed, 

There should be 4 on a  75.  The fourth is  a coolant Temp switch which could be placed on the side of the housing or in the front.

Edited June 15, 2020 by zclocks

[Bigz Zee]

I have a solid list of things to check, thanks everyone, I'll update on my findings.

One more bit of info/question. Should there be a gasket on the Oil Fill Cap? My cap does not have one, it's just hard plastic. I saw a comment about the oil cap on the "Car can't go up hill" post

[Zed Head]

No gasket, just plastic.  It seals very well.

[chaseincats]

For the record, you don't need a spare spark plug to test spark.  Just unplug the center lead on the distributor cap and hold the metal spark plug connector next to the body metal.  No need to find/buy a spark plug to test.

[Captain Obvious]

3 hours ago, Bigz Zee said:

Should there be a gasket on the Oil Fill Cap? My cap does not have one, it's just hard plastic.

Yes there should be a seal on the cap, and I bet you DO have one there. It's just hard as a rock from heat and age and it looks and feels like it's hard plastic and part of the cap. But in fact, it's a separate piece.

#40 GASKET-OIL FILLER CAP  -  15270-78500 

Note that the early cars (through mid-71) used a different number, but from that point on, everything used the 15270-78500.

[Captain Obvious]

Thinking about it a little more, there is also the possibility that yours got so completely petrified that it cracked into pieces and fell off sometime in the past. 

 

[Zed Head]

Good catch.  My Z didn't have one and never had a problem.  The surfaces were both flat and sealed perfectly.  It was actually a satisfying piece of plastics production. 

http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/cylinder-head

Edited June 17, 2020 by Zed Head

[Zed Head]

2nd edit, actually a post...just curious.  I wonder if people could pop their caps and see if they have rubber on there.  To CO's last post's point.  Just one of those curiosities.