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Bigz Zee

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

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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.

 

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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.

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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.

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Posted (edited)

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.

thermo-house.jpg

Edited by zclocks
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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

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No gasket, just plastic.  It seals very well.

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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.

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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.

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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.  LOL

 

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Posted (edited)

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 by Zed Head

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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.

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Just now, Zed Head said:

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.

TBH I didn't know there was supposed to be a gasket there either.  The gasket seems to be NLA though...

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I have one on my cap. It's a black washer and if you poke at it with a screwdriver tip you can see that it's not quite as hard as the plastic cap, but it's pretty hard. Maybe 1/16 inch thick? ID is a snug fit on the threads, and the OD is about the same size as the raised boss on the valve cover?

I don't know how compliant they were when new so I don't know if it was always that hard, but I suspect it was slightly more compliant years ago. Every Z I've messed with has had one. I think you might just be not realizing it's there. It's really easy to mistake it for "part of the cap".

I'll take a pic tomorrow if someone doesn't beat me to it.

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4 minutes ago, Captain Obvious said:

I think you might just be not realizing it's there.

Nope.  I looked closely because I thought that there should be one.  Then I thought "what a fine piece of engineering and manufacturing".  The reality is that they didn't need one there, as shown by my leak-free cap.

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I saw this image before and looked at my cap. Mine looks like one piece. I thought about poking it with a screwdriver. I need to take another looks at it. I see a little oil around the cap, and was thinking about getting a more pliable seal.

The seal on my 240Z is more obvious.

S30-025-01.jpeg

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Posted (edited)

I got one, thought it was part of the cap, pretty hard, but it def is a separate piece. the drawing make it look wider than it is.

 

Edited by Dave WM

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Right. It's easy to mistake it for part of the cap. Here's some pics.

Cap, as it's normally seen:
P1170026.JPG

Close up of the seal in-situ. Looks like all one piece:
P1170027.JPG

But in fact, it's not. Used a thin blade to get a little separation and get things started, and the seal comes off. Note the step on the seal and the recess on the cap. Speculation on my part, but I bet the earlier seals (with the different part number) didn't have that feature:
P1170028.JPG

P1170029.JPG

And here's a close-up of the cap with the seal removed. You can see the recessed area for the step.
P1170030.JPG

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Could be I missed it.  I sold the car so can't check.  How does it seal without the rubber piece?  Did you try it?

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46 minutes ago, w3wilkes said:

The seal on mine is in the valve cover. Car is 12/70 date.

IMG_20200617_103638789.jpg

 Ditto, 10/70 build date.

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9 hours ago, Bigz Zee said:

Mine looks like the last pic, with the seal remove.

Yeah, then yours probably petrified and fell off some time in the past.

And for the guys with the O-ring style built into the valve cover, I guess that's the older style. according to the documentation, they changed over to the newer style in 71.

 

 

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I have had heat soak problems in the past and someone suggested changing the 'coolant temp sensor'.   Seemed strange but it helped correct the problem.  Don't buy aftermarket ones, they don't hold up.  Buy OEM parts.....

Hope this helps!

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Those oil filler cap seals have been NLA for about 2 years. The oil filler cap O rings have been NLA for more than 15 years.

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