I have a 96 GS that I don't drive much. Last weekend I took it to a 80/90's car show and it was very hot outside. No issues with the car at all. When I got home, I unscrewed the gas cap while the car was running and was amazed by how much pressure was in the tank. It blew out for a good 30 seconds and the tank was about 1/2 full. I had an 89 C4 for years and never had this issue.

So I started looking on here about EVAP issues and learned that the canister can leak carbon pellets and clog the line to the engine. I also learned that there is a purge solenoid on the side of the manifold. It's a normally closed valve. I took mine off and cannot blow through it. There is another solenoid between the what I'm calling the main one and the line from the canister. It has a pancake type looking valve at the top and is electrically operated. I can blow air through the hose and through this primary valve all the way back to the canister so it must be a normally open valve. I don't know why there are two next to each other. So I'm assuming that my line is not plugged with carbon. The Factory service manual was no help in diagnosing high pressure in the tank without a code.

So if I can blow air from the engine back to the canister, it must be open all the way to the tank right? The only think I can think of is that the solenoid is not opening when 12V is applied. I did replace the valve and went for a 15 minute drive last night and there was no pressure. However, it was cool out so I don't think it was an accurate test.

Is my logic correct here and does anyone know why three are two solenoids on the line before entering the throttle body?

Thanks

 

My GS has been doing this since I bought it new in '96. If it is only on hot days after a long drive then I would not worry about it. Mine has lasted 25 years this way without a problem.

 

Really? Well that sounds like the perfect solution. Do nothing!

 

You have basically stated that your car engine is running with no issues at all. But you have the pressure build up (gas cap being removed) in the tank only on hot days after driving the car a while.
I am only telling you that mine has been doing this since my car was brand new (25 years).
Does that mean there was something wrong with it 25 years ago?
If you think so then troubleshoot to your heart's content. It will be interesting to see what you find wrong.
Good luck

 

You took my response out of context. If yours has been like this since new, then I’m not going to fool with it. I’m not wanting to mess around and chase a ghost so I’m happy to do nothing.

 

I apologize for the misunderstanding!

 

Mine builds pressure, also. The replacing of the evap cansister is not the easiest thing to do but not too bad. It is located in the RR behind the inner fender liner. Did mine only as a maintenance item. Thought I had a problem there but ended up being crankshaft position sensor - it was evidently cracked and would throw O2 sensor codes when engine was started while hot. Also, the engine would hit a hard lick and stop rotation upon trying to start. New CPS solved all the ills. Strange. (just a little extra info).