Excess Pressure in Fuel Tank

I have an '87 RX7 NA that has a pressure build up problem in the fuel tank. The car is a track car and last fall while on track it built up enough pressure that it was pushing fuel out the filler neck with just a half a tank of fuel. I had forgotten about this until a couple of weeks ago at the track when I was refueling and as I removed the gas cap it released a lot of pressure, 30-40 seconds of hissing. In doing some research it looks like it may be the check and cut valve (located at the fuel tank) or the charcoal canister that may be allowing pressure to build up. Any chance the check and cut valve is located behind some access panel I can get at from the hatch area? I have a factory service manual but I can't find a reference for trouble shooting excessive pressure build up in the fuel tank. Has anyone experienced this and where is the best place to start trouble shooting? Any other things to check/test?

Check your gas cap. My old Datsun had a pressure relief valve on the gas cap. It was a '79 though, so I'm not sure if that's an old car thing. check it by sucking on the valve on the inside of the cap.

If it's an issue with the lines/charcoal can/etc, I would just run a line an vent to the atmosphere (1950s style). It is a track car.

+1 for vent line

Vented gas caps are an old car thing...it's a track car so if you don't feel like going out of your way to make a car that doesn't drive much environmentally friendly, you can run a vent line. Your gas will evaporate a bit and get varnish-y faster though.

BE CAREFUL WHERE YOU VENT IT!!!!!!

My GTV (the gold car in my avetar) had the vent lines that ran from the tank/cannister to the engine break, which resulted in fuel being sprayed onto my brakes.

Hot day on track, plus hot lapping = fire. Even as I drove to the safest corner worker, I left a fire trail behind me as the fuel boiled and came out of the venting system.

And even after the fire was out, the tank boiled for quite a while- I spent a lot of time cooling the tank off.

If your car has a venting system, I'd suggest finding the plug and cleaning it up. Burning the vapors in the engine is the safest palce to do it.

Use a bic lighter to be able to see what you are doing and then drill a small hole in the top of the tank. It will relive the pressure spectacularly.

1987 FI Rotary Engines:
http://mazdarx.narod.ru/manual/EMISSION_CONTROLS.htm

Disconnect and remove the check and cut valve. Blow into the valve through port Aand make sure that air comes out of port B. Block port Band confirm that air comes out of port C. Block port Band draw air through port A. Air should pass through from port C. If the valve does not function as described, replace it.

N Sperlo wrote: 1987 FI Rotary Engines: http://mazdarx.narod.ru/manual/EMISSION_CONTROLS.htm

Disconnect and remove the check and cut valve. Blow into the valve through port Aand make sure that air comes out of port B. Block port Band confirm that air comes out of port C. Block port Band draw air through port A. Air should pass through from port C. If the valve does not function as described, replace it.

Thanks, I had found this in my manual. I wasn't sure which way this valve would affect pressure. I had thought it might be the cap was the problem but it should be creating a vacuum if it was blocked. My thinking was a vent issue would cause the pressure to want somewhere to escape. Now the question is where is the check and cut valve. Will have to start hunting for it, hopefully somewhere easy to get to. Thanks for the replies.