vapor lock?

[76Datsun280z]

It's about 75 here today and I ran a few errands with my Z. After the second errand, it was really really hard to start, I barally got it going. After I got it going, it ran fine as usuall home. So after I got home, I could smell a lot of gas fumes comming around from the gas cap, so I thought I'd unscrew it. Immediately as I unscrewed it, it went "KA BAM" and shot off really hard and you could smell and see all of the fumes comming out. After I took the cap off, I wanted to see if it would start, and it fired right up, no problem. I assume this is vapor lock? This has never happened before, and I assume it's because of the heat? What may have caused this, and what do I do to prevent it? I'm going to call a local Z guy to see what he has to say about it too. Thanks again with all your help guys.

[76Datsun280z]

I talked to the Z guy about it and he said that it is a really common problem with the efi cars. He said the carbon canister can get plugged and said to take the hose off labled "fuel tank" and to hook a hose up to it and blow inside there with low air pressure with your mouth with the gas cap off. I did that a few times. Another thing he suggested which I am having trouble understanding is you can put a quart of motor oil into the gas tank. Wouldn't you be just blowing blue smoke like crazy I asked?? But he said it wouldn't really have an effect with 17 gallons of fuel.:nervous: He said you can buy a fan for the injectors that's made specifically for these engines and if I remember correctly mounts on the fuel rail or something. I'd like to see a picture of this if anybody knows what I'm talking about.

[76Datsun280z]

I think this is what he is talking about here.

http://cgi.ebay.com/ebaymotors/DATSUN-280zx-FUEL-INJECTOR-COOLING-FAN-ASSEMBLY-L-k_W0QQitemZ320100506921QQihZ011QQcategoryZ6763QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[Cethern]

I have the same problem the local Z tech told me it is a check valve by the fuel pump not holding line pressure. But it sure feels like a vapor lock problem to me. The blower motor helps right now mine is set to come on with the ign key goes to run.

A friend thought it may help to run a hot wire to the pump with a switch so I could get some cooler fuel though the system before I start it.

Here is a pic as to how the blower mounts to the motor.

[sblake01]

There is no such thing as vapor lock on a fuel injected car. The fuel pressure is high enough to prevent it. The purpose of those fans was not to prevent vapor lock but to lower the temperature of the fuel mixture which supposedly lowers emissions. If the fans were there to prevent vapor lock then why were't they also on the 810s and Maximas built for the 79 and up model year? The attempt to lower the temp of the fuel mixture on those cars was done by having the air intake above and away from the heat of the radiator.

[Cethern]

I know "they say" but this is the second FI car that has had the same problem

the other was a Holly Projection system I had on a 76 FJ-40 with a 400sbc. in both cars there is a lot of heat. When the cruiser would vapor lock I would open the inlet fuel line and most of what would come out would be what seemed to be air but is the gas vapor.

The way I have used the fans in cooling off the fuel rail does help or at lest I think it does. I do see a difference in the way things get started without the blower.

Now there could be a check valve that is not holding line pressure It must be by the fuel dampener (sp) Unless it is part of the fuel pump and now that I think about it I have a spare pump in my 76 that I just got, I'll get out and take a good look at it.

[280z1975]

My car came with a heat shield which attaches to the manifold. It helps to separate the heat from the engine's fuel lines and fuel injectors. I plan to further add some heat shield padding to it just to make it that much better.

I have experienced the same problem with my car when I first put it back together, but after it did it two of three times all was well. I figure it must have been something that was loose (a wire or bad connection) and put it back into place when I was cleaning up things and fixing connections. I'll let you know if the problem comes back any time and what I do to fix it, but I doubt as it was fairly warm all summer and the car ran fairly well.

[sblake01]

I know "they say"............

This is not a case of 'they say'. I'm telling you fact. And I'm not talking about 'Holley projected Chevys', I'm talking about 75-83 (84 if you count the Maxima) Nissan EFI. If you think the fan works for that purpose that's fine. I have two cars w/o injector fans and I've never experienced vapor lock. And I live in Southern Califronia and you know how hot it gets here in the Summer. I've had the symptoms you describe on my 810 but it was caused by a bad check valve. If the check valve doesn't hold, the fuel pressure has to build up before the car will start except when it's cold when the cold start system will get it going. This is the location of the check valve.

[wa5ngp]

You may have some heat related problem or bypass or relief valve problem but you don't have what is considered the classic vapor lock problem that happens on carbureted Z cars. I've had a lot of it on my 73 with 72 carbs. The way I ultimately fixed it was to install a flex fan for the radiator. I've also added heat shielding underneath those Su's.

I have an 81zx also. The most similar experience I had was a failing fuel pressure regulator. After a long highway run and a quick stop it would often stall. I figured out that it was the regulator by noticing that when I turned the motor off that the fuel hose stiffness when way soft real quickly.

I also got the message while perusing the junkyards and noticing that most of the wrecked FI models seemed to have a new(er) regulator so that tells you that its a common point of failure.

Living in central Texas the aux FI fan came on occasionally. In the summer I bypassed the thermostat so that it came on every time. I just figured cooling that whole area off more quickly in the summer has to be a good thing for life of all that stuff.

See if you can check out that regulator.

best of luck

Don

[sblake01]

I guess I didn't address the original question. I get so fired up when I hear someone mention vapor lock on the EFI cars. Take the carbon canister out being careful not to break the plastic nipples that the hoses plug on to. Remove the filter from the bottom and soak it in in solvent and dry it out. Spray carb cleaner into the nipples on the canister and blow them out with low pressure comprssed air. Reassemble everything and you should be good to go.

[76Datsun280z]

I guess I didn't address the original question. I get so fired up when I hear someone mention vapor lock on the EFI cars. Take the carbon canister out being careful not to break the plastic nipples that the hoses plug on to. Remove the filter from the bottom and soak it in in solvent and dry it out. Spray carb cleaner into the nipples on the canister and blow them out with low pressure comprssed air. Reassemble everything and you should be good to go.

Thanks, I'll see if I can pull it off tomarrow and do that.

[76Datsun280z]

So to remove the filter below the canister, do you unscrew it? I guess I'm confusted on how these come out.