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Thread: What to do about vapor lock

  1. #1
    Registered User ROOPZ's Avatar
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    Default What to do about vapor lock

    Hello Everyone!

    I am wondering if there is anything I can do to stop my car from vapor locking. I believe that is what is happening. It runs sweet most of the time. Sometimes it will die while going down the road but that is a different story. What is embarrassing me is the re-starting after sitting a few minutes. I go to a store or whatever, go inside for a few minutes 3-10 minutes, come outside, get in, and start her up. Usually she doesnt protest starting UNLESS you let it die, then you are screwed for a few more miinutes. If it starts, it runs R-O-U-G-H at idle and doesnt take the throttle very well. You have to baby it some. It takes about 2-3 minutes atleast for this to subside and then it will run fine. It is a 78 280Z with all stock engine. I cant possibly be the only one who has experienced this.
    Also, has anyone experienced the car just dying abruptly while driving down the road and then kick back on a few seconds later? I cannot for the life of me find a reason for this other than the car doesnt like me!
    Any advice is greatly appreciated.
    ROOPZ

  2. #2
    Registered User tanny's Avatar
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    Default

    Your problem could have many causes, but here was my solution to vapor lock on my setup, which is a 240 with triple Webers. Installed heat shield over headers, 1/2 inch foam water pipe insulation over all rubber fuel hoses, radiator shroud, electric and mechanical fuel pumps, and hooked up fuel return line. Have no idea which remedy worked since I did almost all of this at the same time, but it definitely solved my vapor lock problem. Good luck, Victor.

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    I would be very surprised if this is a true vapor lock probelm on a 78 with FI...
    It sounds to me more like either an ignition problem or a fuel injection problem. It could be a combination of both, or one problem that affects both.

    First thing I would do, is to do a complete and thorough tune up, including replacing the coil. Check all vacuum lines and replace any that are questionable. Check all the wiring harness connections for looseness and/or corrosion, probably all the way back to the ingition switch to be sure it's not something simple.

    If that doesn't help, you'll need to trouble shoot the FI system, especially the temperature sensors, AFM, and fuel pump relay and pump itself.

    If you don't have one already, before you start, get yourself a Factory Service Manual. I can't begin to tell you the benefits of having a good manual when troubleshooting the FI and elctronic ignition on a 280.
    "If it weren't for fools, the rest of us could not succeed." Mark Twain.

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    How does the car crank in the morning when absolutely cold?The car is not vapor locking.Thats a carb thing.I vote fuel pump or pump relay.You can buy a pressure gauge that goes on the fuel line.I think the number is 28lbs. that it should hold at all times.If the pressure drops it doesnt have enough pressure to pop open the injector.Or worse the fuel drains back to the tank and must be pumped back up.

  5. #5
    Registered User sjcurtis's Avatar
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    Default ignition lead

    ROOPZ,
    you have a black lead from the coil with a two pin plug clipped to the distributor on the forward side ( nearest the fan), it is the ignition wire from the coil.
    now you now what I am talking about I have one question and I think I am probably right is this lead hanging below the intake air pipe from the Air flow meter, if so it is to heavy and occasionally will give a bad contact. Run this wire over the inlet plumbing and make sure the crimp inside the plug engages firmly and your problem should be gone for good.

    cheers
    Steve

  6. #6
    Registered User ROOPZ's Avatar
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    Thanks Guys for the replies. To answer your questions, In the morning or after sitting for quite a while, 2 hours or more, it will start right up and run beautifully. I have done a complete tune-up including new coil, plugs, original nissan wires, cap, rotor, fuel pump, filter, injectors, ignition switch. I checked the wire you suggested, sjcurtis, and it is already ran over and secured. I have not changed the fuel pump relay or the fuel injection relay or the AFM and I am planning to do that soon. I have the cd-rom version of the factory service manual and I agree it is invaluable. I have run the tests it gives for ignition and nothing is wrong according to the results. My Z is my daily driver so I want it to be dependable. Not that is isnt but I am afraid it will get to the point where it will refuse to start back up. Anyway, Thanks for all the suggestions!
    ROOPZ

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    O.K. major tune up done huh? Knowing now that it likes cold starts and hates hot makes me wonder. First I'm not the efi man.I do have a 280zx book and maybe the parts didn't change much.They show a "thermotime" switch that lives in the thermo housing.It senses water temp and if cold supplies a voltage(via grounding) to the cold start valve.The cold start injects fuel.It is located in the fuel rail.I would unplug the cold start valve and try when hot.The sluggish doesn't want fuel may be cause its flooded.If it cranks you then know its somewhere between the thermotime and the cold start valve.I love good new parts but don't just throw them at the trouble.It cost like hell and you may add new troubles along the way. I now vote the car always thinks its cold thats why it cranks so well when it is and doesn't when its not. Let me know!
    Last edited by Daniel; 11-03-2003 at 11:53 AM.

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