porshaowner

Title explains the problem. There are check valves in the right rear pillar. One is a rollover valve and one is a check valve. The check valve holds the pressure in but will allow the tank to draw in fresh air thru the charcoal canister system. Hot days or driving on the track create the worst pressure. It is not a little pressure it is alot. Has anyone had this problem and can tell me what is broken in the system?

Thanks

CO951

I've had the problem, and it seems to be very common. The others I've talked to about it who've been running these cars for years tell me to loosen my gas cap. That works for the pressure, but then I get gas running out and down the fender on hard left handers. I think I need to find a venting gas cap.

Team SSR

FWIW the vented gas cap I use lets some fuel slosh out also.

fatbillybob

loose caps cause fires on rollover when they come off or leak. Rollover valve is a check valve. The other is maybe a vent valve. Most vent valves also have check valve feature. Maybe your vent valve is just bad. There is just 1 atm of pressure plus vapor pressure that vents to the charchol canister then is pulled into your intake as part of a closed smog system. You need to make sure all electic solonoids if any are working and hoses are intacted so that the system function properly for proper venting. Otherwise you need to redesign the system if you are dumping some oem parts or you need to go to a properly vented fuel cell. Gas tanks and their design is part of your safety system think before you modify them.

Bill L Seifert

I know it is hard to describe a problem. My 944 hisses for about 4-6 seconds when I unscrew the cap. I was told this is normal. Is your's more than that?

Bill Seifert

1987 944S Race Car

jim3

10 years or so ago in the conn valley region's challenge monthly mag there was an article where the gas tank collapsed in and I seem to remember there was a valve on the driver's side in the engine compartment in front of the fusebox that was eventually diagnosed as the problem. I tracked and raced 944's from 1985 thru 2006 and never had a problem, so something is amiss and I agree with fatbillybob, don't fool around with home made venting remedies

Team SSR

Bill, Your hissing sounds like air going into the tank indicating vacuum in the tank. Porshaowner has pressure. I went to the vented cap because I have the charcoal system removed. Over the course of a weekend on track it leaves a small trail on the quarter panel where you can see gas has leaked out. I do have the factory plastic check valve in the filler neck, but the fuel nozzle filler restriction has been removed for quicker refueling for enduro events. I will need better slosh protection or a better vent system.

Bill L Seifert

You're kidding. I didn't know that. I guess you learn something everyday.

Bill