Gas Pressure

[Jim Keaty]

I recently put a new engine in my 1988 345 classic. I seem to have a Gas pressure problem. When I go to fill up after a long hot ride my gas tank seems to build up a lot of pressure so much that when I unscrew my gas cap it blows the cap out. I have changed the gas cap to a vented gas cap but I think it only vents one way and prevents the gas pressure from venting from the tank.

Question: Should there be another vent in the system to prevent this gas pressure from building up?

[martin300662]

Join the club Jim!

Apparently, in the early Argosy years, the problem was severe enough to split tanks and require replacement. If you look at my rebuild thread you will see I had severe leaking on a brand new custom tank that I now attribute at least in part to the same issue and have had the pressure build up significant enough to actually blow the cap off as I released to refuel.

My current solution (working so far) is to score the cap gasket from inside to outside to create channels that allow pressure release. I occasional get a slight 'hiss' as I remove the cap, but to me that is good because it means the tank is not continually venting only releasing excess pressure.

[bkahler]

Jim, did this problem only show up after replacing your engine? I'm not sure I can see a tie to engine replacement and gas tank venting issues. On your 88 there should be several vapor canisters and if I remember correctly they are located in the right front wheel well area. If one or more of those hoses got damaged, capped off, crushed, etc. that might be the cause of your tank not venting properly.

The bottom line is you're going to have to trace the lines for your fuel tank and emissions system to make sure they are in good shape.

[WayneG]

This is probably no help on a 88 with all the emissions stuff but on the pre-emmissions setup like my 84, mine just had a vent hose from the top of the tank, along the frame toward the rear, no fitting, no canister, no nothing.
When I added an in tank fuel pump I kept the vent hose, but added a roll over valve to the end of the hose and mounted it above the rear bumper.

[Jim Keaty]

I do remember my mechanic saying he removed a portion of the emissions system that was near the wheel well. He said it was not something we needed at least in Louisiana. I think I remember seeing a large canister that was part of the system. Do you think that would be the problem. What does the vapor canister look like?

[bkahler]

I always cringe when I hear a mechanic say it's not something you need. Unless they know exactly what lines they're messing with and what they do it's usually best to leave well enough alone.

I'm not saying this is exactly what you had but it should give you a good idea as to what the canisters look like. Different years used different canisters with different ports.


My guess is your mechanic plugged the vent for your gas tank when he removed the stuff you didn't need

[Jim Keaty]

Thats exactly what he took out

[bkahler]

If you're going to leave the canister(s) out then each pipe or tube that was connected to the canister needs to be researched so you know what needs to be done with it. Some can be capped but as you've already found one or more needs to be vented somehow and others may need to be routed to a different location.

Good luck!

Brad