I've been away from the board for a few years (no computer), but it is nice to be back and see some names I recognize.

Here are my problems: I have an '85 IROC that is leaking fuel out of the gas cap. The car is also building pressure in the fuel tank (I think the tank should be held at a slight vacuum?). After the car has been run and the gas cap is removed, the vapors escape with a rush. I suspect the pressure buildup is causing the fuel leakage. Any ideas about the cause(s) for these problems?

PS: These problems started after I replaced the fuel pump. I have checked the fuel lines/hoses and I am rather sure I reconnected things properly.

Some details: '85 IROC with 355, Superram, adjustable fuel pressure regulator, many other mods but none affecting fuel system.

Chuck

 

have you replaced the tank pressure relief vavle? i just replaced mine friday and it has gotten rid of the pressure at the cap and the fuel smell it had. if the tank was full i did have an overflow problem. i am going to go fill it to the rim and make sure it is cured today.

GM discontinued the part number for the earlier models, like yours but i talked to the guy at the parts counter who has a 85 matter a fact and he said the 1 i ordered for my 89 looks exactly like the discontinued 1. he is even going to get 1 for his car since his is shot too. my old vavle still worked after i removed it but for some reason it just wasnt venting correctly, maybe the valve was starting to stick.

 

well here is some results from a top off today. i have no pressure issues at the cap like i did and for once when i capped it off it didnt overflow, but i still leak some gas making right handers. must be a filler neck problem, someone pried on the filler neck taking off a gas cap at some point.

 

Thanks for the advice Turtle.

I did replace a part GM calls a fuel PSI solenoid, part number 10033125. It connects to a rubber hose that comes from the fuel tank and mounts in a "U" shaped bracket near the left rear tire. It looks like it would function as a check valve.

Does this sound like the relief valve you replaced?

By the way, I also have a dent in the filler neck (my fault, some bad advice I got). I have wondered if this is the cause of the leak but I can't understand how the cap can hold vapor pressure but still allow liquid fuel to escape???

 

well sounds like you have already replaced it then. the problem i see with these caps is the way the cap seals, if the dent is on the edge of the neck or the neck is out of round it leaves a gap around the gasket. it may still make contact and hold back some pressure but if just sloches up it may leak out (seems to be my problem). depending on how bad the dent or out round it is will determine how well it seals.

replacing the valve did allot for the excess pressure i had in the tank now i just need my cap to seal on the neck better and i think i will be perfect. i am also wondering if i can find a different kind of cap the dont seal inside the neck but on the surface edge that will fit. surface edge caps are more substantial and seem to seal better to me, they also dont need a relief valve to vent pressure. i've had cars with incredible pressure under the cap when nearly empty.