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Gas Smell


beebow's Avatar
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05-18-02, 01:25 PM   #1  
Gas Smell

Here is my problem; I have a 92' Camaro Z28 that smells of gas from the rear. The smell is coming, I believe, from the gas tank pressure relief valve. This sound simple, but the relief valve should only open under extreme pressure. The gas smell is intermittent, sometimes while the car is moving and sometimes when you shut the car off. There is a pressure relief valve located near the charcoal emissions cannister. Is there any way to test for an intermittent restriction in the emission system that may be causing the high pressure in the tank?

 
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dirty dan's Avatar
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05-18-02, 05:27 PM   #2  
Curious Problem.
Are you sure it's high pressure in the tank? Have you removed the gas cap to be sure?
In my mind a more likely problem would be a hole in, or a disconnected vent line or possibly a bad gas cap. How is the fill hose from the gas fill to the tank? What happens if you remove the vent line to the carbon canister? If you think the hose is the problem, disconnect the vent line from both the canister and the tank and blow air through it.
Let us know what you find.

 
beebow's Avatar
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05-18-02, 10:04 PM   #3  
I removed the purge side hose from the cannister with the car running and had strong vacuum, on the tank side port there was no noticeable vacuum. I did the same thing on my 95' GMC truck with the same results. Earlier today I changed both the fuel tank pressure relief valve and the pressure relief valve near the charcoal cannister; both new valves seemed to act like the original ones when I blew through them. Is there an internal valve in the cannister that doesn't allow the tank side to be drawn on until enough pressure passes through to the cannister? Should I be able to blow through the cannister from the tank side? Thanks for your response Dan.

 
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05-20-02, 08:04 PM   #4  
rickwhoo
did you check the hoses from the gas fill to the tank for leaks or loose clamps?

 
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05-20-02, 09:54 PM   #5  
I'm not 100% sure, but I think that the fuel line to the canister should not be under any pressure except slightly higher than atmosphere. The carbon canister is to allow the fuel vapors to vent slowly through the carbon to remove VOCs. I would not try to blow through the canister with compressed air because it is not made to take that kind of volume of air/vapors. Any purge or effluent from the canister goes back through the engine for incineration. I sincerely think that your problem is a hose or cap. Why do you think that the fuel tank is under a high pressure? What is the cause of the pressure?

 
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05-20-02, 10:39 PM   #6  
I changed all of the hoses coming from and to the tank. This system is designed to work on positive pressure and should have a release when the gas cap is removed. I did some reading up on the evap system and found that the purge side is only activated when the vapors are built up in the cannister, and the engine reaches temperature. The purge solenoid opens and allows (as you have said Dan) for the vapors to enter the engine. The fuel tank pressure relief valve is the only release for tank pressure when the car is turned off, and the fuel pump shuts down. Since the tank is used as a heat sink for the hot return fuel, additional pressure is created. The fuel pressure valve near the cannister allows the vapors to enter the charcoal cannister, and if the pressure is to high a relief valve within the pressure valve allows the vapor to return to the tank. Well at least this sounded good to me. I changed all of the hoses, and both valves. My thought on the problem is that the tank relief valve is fatigueing. So far no smell, I will let you guys know if this returns. Thanks for the advice it is greatly appreciated.

 
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