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Why would my 1985 C4 build up Way too much pressure in the tank?. When i loosen the gas cap it will take at least 40 seconds, sometimes more, for all the air pressure to vent from the tank. Is this normal.I mean its under A LOT of pressure. Why does this happen. The cap has been tested and passes emission standards. Whats up....

Thanks , JS
 

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I'm happy to hear you weren't smoking a cig. the first time it happened, as for the cure I'm sure someone with more experience with this problem will step in. Usually on a hot day, I've heard that noise for just a few seconds, that's normal. But your condition sounds a bit alarming.
 

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Discussion Starter #3
Unreal

I'm happy to hear you weren't smoking a cig. the first time it happened, as for the cure I'm sure someone with more experience with this problem will step in. Usually on a hot day, I've heard that noise for just a few seconds, that's normal. But your condition sounds a bit alarming.
I'm telling ya man, I just stand there listening to this thing venting and venting. Its unbelievable. While its venting, one little spark and i'm done.
WOW. The pressure is just too much. I'm stumped.
 

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I believe the gas tank is actually not under pressure but under suction. When emptying the tank of fuel it has to replace the space where the fuel used to be with air. If there is not proper venting of the fuel tank to allow this then I believe it will be under great suction and when you take the gas cap off you are actually hearing air going into the gas tank rather than leaving it..... just my thoughts......
 

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Discussion Starter #5
Makes sense

I believe the gas tank is actually not under pressure but under suction. When emptying the tank of fuel it has to replace the space where the fuel used to be with air. If there is not proper venting of the fuel tank to allow this then I believe it will be under great suction and when you take the gas cap off you are actually hearing air going into the gas tank rather than leaving it..... just my thoughts......
I'll tell ya bro, i can feel it coming out from the tank and actually see those really really flammable fumes coming out like the phony heat lines coming off a really hot highway from a distance. WOW.
 

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Why would my 1985 C4 build up Way too much pressure in the tank?. When i loosen the gas cap it will take at least 40 seconds, sometimes more, for all the air pressure to vent from the tank. Is this normal.I mean its under A LOT of pressure. Why does this happen. The cap has been tested and passes emission standards. Whats up....

Thanks , JS
i would think the tank vents into the charcoal canister in the engine compartment so i would guess you have a pinched vent line or a defective canister
 

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Your car should have EVAP canister in front of the left front wheel it has lines and a electric actuator. The ecm should tell the system to purge when certain conditions are met. It sounds like your system is not purging. I assume there are no codes {SES light} on. I would suggest checking the lines and the canister and the switch that purges it. I believe my switch is mounted on top of my thermostat housing back bolt. I don't know if your car is the same as my 1988. I hope this helps.:thumbsup:
 

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Your car should have EVAP canister in front of the left front wheel it has lines and a electric actuator. The ecm should tell the system to purge when certain conditions are met. It sounds like your system is not purging. I assume there are no codes {SES light} on. I would suggest checking the lines and the canister and the switch that purges it. I believe my switch is mounted on top of my thermostat housing back bolt. I don't know if your car is the same as my 1988. I hope this helps.:thumbsup:
:agree: Except the part that is bolted to your stat is for the EGR diaphragm.

This is from my 86 manual
http://members.shaw.ca/corvette86/Evaporative Emission Control System.pdf
 
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