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Gas cap?

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Old 02-15-2017, 02:21 PM
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Gas cap?

I have a 78 280z fuel injected 5 speed. Just got it in a trade. Flunked ca smog so I changed all the old gas tank engine hoses (they were in bad shape). Changed filler hose. Drove it 30 miles to re smog. It ran really bad at idle. Frustrated driving home started acting like it was running out of gas. Nursed it home barley......half hour later started right up but ruff. Removed the gas cap with a whoosh. Runs great now. Does the cap have a relief valve in it? I don't understand... Help..... Bj
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Old 02-15-2017, 05:38 PM
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You'll have to take a look at the factory service manual (FSM) for your car. That whoosh is because now that you've replaced all those leaky hoses, your fuel system is sealed up and it's not supposed to be. As fuel is drawn from the tank, no air gets in so it becomes harder and harder for your fuel pump to operate. When the car sits for a while, tiny air leaks will eventually equalize the pressure and the car runs again. If you open the filler cap, the whooshing is the sound of air rushing into your tank.

Typically there's a vapor collector in the right rear of your car, above the filler. IIRC, there are two hoses from the fuel tank that connect there. A third hose goes from this collector to a charcoal canister in the engine bay. This third hose and the charcoal canister usually supplies the pressure relief to your system. The manual will tell all.

You can get a copy of the FSM for the '78 here: http://xenonzcar.com/s30/files/FSM/1...280z%20FSM.zip

Take a look around that site. There's a lot of good information for Z owners. Welcome to the club!

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Old 02-16-2017, 09:22 AM
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Thanks. I thought about drilling a small hole in the cap..... I'll try the web site and figure out how the canister works. must be a filter clogged in there. The car sat since 2013 and was in poor health before that. Runs great then runs ruff. new plugs wires I guess it time to check out the injectors and filters along with the vent system. bob
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Old 02-16-2017, 09:38 AM
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Originally Posted by bjretired View Post
Thanks. I thought about drilling a small hole in the cap..... I'll try the web site and figure out how the canister works. must be a filter clogged in there. The car sat since 2013 and was in poor health before that. Runs great then runs ruff. new plugs wires I guess it time to check out the injectors and filters along with the vent system. bob
I'd counsel against drilling the hole in the cap, especially if you want to pass CA emissions.

The canister does have a replaceable filter underneath. Last I saw, MSA (thezstore.com) has them. You should check to be sure the line to the filter isn't clogged. Oh yeah, somewhere in that line should be a little known flow restrictor. Its purpose is to keep the vacuum from drawing too much vapor into the motor. I had to make one myself, what a pain.
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Old 02-27-2017, 08:46 AM
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Gas Cap

Originally Posted by beg3yrs View Post
I'd counsel against drilling the hole in the cap, especially if you want to pass CA emissions.

The canister does have a replaceable filter underneath. Last I saw, MSA (thezstore.com) has them. You should check to be sure the line to the filter isn't clogged. Oh yeah, somewhere in that line should be a little known flow restrictor. Its purpose is to keep the vacuum from drawing too much vapor into the motor. I had to make one myself, what a pain.

Thanks for the advice, the problem was a clog in the vent line? blew air through it and it finally broke free. Ordered a new canister filter. and replaced all the old crystalized hoses. I got carried away and went through the injections replacing the injectors, seals and regulator and filter.....I had to take it apart to change the hoses anyway. If your going to be a bear be a grizzly....bj
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Old 02-27-2017, 11:52 AM
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Originally Posted by bjretired View Post
Thanks for the advice, the problem was a clog in the vent line? blew air through it and it finally broke free. Ordered a new canister filter. and replaced all the old crystalized hoses. I got carried away and went through the injections replacing the injectors, seals and regulator and filter.....I had to take it apart to change the hoses anyway. If your going to be a bear be a grizzly....bj
Good for you, glad you found the problem Mr. Grizzly.
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