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Discussion Starter #1
Bet you guys are tired of seeing me here right? Almost all of the issues since I bought the car have been eliminated but as the temperature starts creeping up (Arizona weather), I've noticed a peculiar issue. After driving for awhile, say 30 minutes on the freeway, I turn off my car. Go to turn it back on 10-15 minutes later, and it has trouble starting. It cranks just fine and starts for about 2 seconds then dies immediately. I can keep my foot on the gas and blip it to keep it alive, but even then the idle will kinda hang around 200-300 RPM. It's not until I actually hit the road again (driving normally) for the idle to get back to normal and it drive as it should. Then it does the same thing after turning it off and attempting to start again shortly after. This does NOT happen at all on a cold or even lukewarm start. On another note, when the engine gets hot, if I let off the gas pedal and let it coast the engine starts bucking about 6 times, feeling like someone is rocking it back and forth. Thanks for any help!
 

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Check your cold fuel enrichment system first. This would include the thermotime switch and the cold start injector, primarily.

The first thing I would do is unplug the cold start injector and see if it makes any difference.
 

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Cold fuel enrichment is a good place to start.

Do you have the stock exhaust manifold, or a header? I have read enough about the fuel rail regarding heat soak issues with fuel boiling in the fuel rail. If your heat shield is gone, more heat could be getting to the rail. If the header isn't coated or wrapped, could be heating up the fuel rail.

edit; saw your other post about the header. I'm thinking this is a heat issue.
 

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Discussion Starter #4
I was thinking it was heat-related as well.... As for the cold fuel enrichment system, this is a 280ZX, not an earlier model. Does this make a difference?
 

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280ZX has the the thermotime switch and cold start valve. The cold start valve enabled for the first several seconds of cranking if the temp is low enough. If after several seconds of cranking and nothing happens, the voltage causes the thermotime switch to warm up just enough so it shuts off the cold start valve to not flood the intake with gas. Below is a photo of the location of the cold start valve. Thermotime switch is located in the front of the engine, near the coolant temp sensor.

 

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Discussion Starter #6
So I went out and checked for any exhaust leaks that may have contributed to letting heat escape into the bay. Turns out that after tightening up the 3 nuts on the manifold to the first pipe on the initial manifold gasket replacement, they managed to back themselves out to finger-tight strength. Yikes. And I could actually feel the exhaust working past the flange. Tightened them up again and added some Locktite. I also bought some rubber washers and some thermal reflective tape for the fuel rail. Hopefully this combined will cool things off enough to where I'm not getting heak-soak related issues (according to the internet and other similar posts that's what's going on). If that's not the case, then I will dig into the valve and the thermotime switch. Will update this weekend! :)
 

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Discussion Starter #7
Ok I have a video of the issue now. As you can see, it will kind of somewhat fire up... but not really. Lol. Any ideas? By keeping my foot on the accelerator during start up I can get it to stay alive and it also smells pretty bad once I get it running this way. NO issues running it cold.
 

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Discussion Starter #8
UPDATE: So from the time I recorded this at 5:52 (It is now 6:17, so 25 minutes later), it starts up no issue.... Its gotta be heat right?
 

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Do you have the injector cooling fan on your ZX? Those were put on to guard against heat soak. If you don't have it (or its not working) that might be the prob.
 

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Discussion Starter #10
Yes I do have it and it is working properly. I was putting two and two together from my last post and I'm wondering if my exhaust leak may have damaged the ICM. The leak pretty big and was due to a missing bolt at cylinder 1 side of the manifold. Who knows how long that was there before I fixed it. And I hear heat-related failure of those modules results in poor performance and issues starting when hot, two things I have been battling since I bought the car in November. The ICM is also stamped with the Nissan badge, so there is a possibility this thing has been hanging on there for almost 40 years!
 

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The injector cooling fan isn't a factor in this because it's not needed unless your engine is at full operating temp, good and hot. I don't think that's the case here...let us know if the engine isn't at full temp.

To me it sounds like you may have a large intake vacuum leak. That often results in this kind of rough running. That might be the case if the bolts which are loosening are the ones that hold down both the intake and exhaust manifolds.

The manifold nuts and bolts can be kept in place with iron keepers.

It took about 5 minutes of searching, but I found some. These go under the nut or on the bolt like a regular washer, but once the nut or bolt is torqued, you pry the fingers up around the head to hold it in place. 280 ZX turbo cars had these on the turbo bolts.

Check it: Bolt Lock, Exhaust Manifold, Pontiac

HAH!! Found the locks for the turbo - if the inside diameter is same as the exhaust studs, and I think it is, these could be used on the exhaust even if you had to separate them.

 

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Discussion Starter #12
The injector cooling fan isn't a factor in this because it's not needed unless your engine is at full operating temp, good and hot. I don't think that's the case here...let us know if the engine isn't at full temp.

To me it sounds like you may have a large intake vacuum leak. That often results in this kind of rough running. That might be the case if the bolts which are loosening are the ones that hold down both the intake and exhaust manifolds.

The manifold nuts and bolts can be kept in place with iron keepers.

It took about 5 minutes of searching, but I found some. These go under the nut or on the bolt like a regular washer, but once the nut or bolt is torqued, you pry the fingers up around the head to hold it in place. 280 ZX turbo cars had these on the turbo bolts.

Check it: Bolt Lock, Exhaust Manifold, Pontiac

HAH!! Found the locks for the turbo - if the inside diameter is same as the exhaust studs, and I think it is, these could be used on the exhaust even if you had to separate them.

How would this only be an issue when hot though? I would think it would be constant if it was a vacuum leak. Plus I just did the manifold gasket and I think I got it done correctly. At least I hope...
 

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The injector cooling fan isn't needed when the engine is cold. All ti does is blow air on the injector rail after you turn the car off. I hope you got those pesky manifold bolts to cooperate this time!
 

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I don’t go with the cold air sensor due to the fact it starts fine when it’s cold your problem is after it heats up

I bet you are suffering from vapor lock and you need to replace Datsun 280Z 280ZX 1975-83 Fuel Thermo Time Air Temperature Switch NEW OEM 434

make sure you clean the terminals well !!
 

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Discussion Starter #15
I think I may have been unclear pilgrim. The manifold to head bolts are just fine. The ones that are loosening are the 3 bolts on the manifold to downpipe flange. Regarding the driveability issue, I will be picking up an ICM from ZCarSource tomorrow since I live like 20 minutes from them. I will report back tomorrow.
 

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Discussion Starter #17
Happy to say, the hot start issue has been resolved! It looks like it was the ICM after all. Did some tests and this new one passed it. This is a $40 aftermarket one so its longevity is questionable, but at least it's good for now. Upon closer inspection of the OEM control module (which I assume since it's stamped "Nissan"), the plastic covering is cracked in various places, almost as if it was expanded or dried out. I think I was onto something there with the extreme heat soak from the previous cylinder 1 exhaust leak next to the module. Bucking is still an issue, but it does this same noise (and I would assume feeling if we were driving it) while idling so that's another problem for another day and probably unrelated to this issue. Thanks all!
 

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Discussion Starter #19
Yes, but the one for the 82-83 in my case. Those two years have the additional electrical connector on the side. Almost tripped me up too when I was looking.
 
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