JC95Z

Ok so my basically stock 95 z runs great when you first start it and she's cold. After she warms up and you have been driving her she will backfire and and chug at first blip of throttle. If i get out and unscrew the gas cap it lets alot of air out and she will run better. Got a new gas cap and still does it. Any Help Please!!!!!!!!

StephenDeli22

It is normal for the gas tank to have that hissing sound of pressure when you take the cap off. I dont think that and your backfire problem is related.

JC95Z

yeah i know there is always the hissing sound when you first take off the cap but this is alot of pressure it will actually let pressure out for about a minute and if i let it all out the car will almost run fine. doesnt make any sense. I actually drilled a hole in the new cap and it wont build up the pressure anymore but it does still hessitate when warm WTF.

WS Sick

Check the tank vent to the carbon canister, there is a solonoid that sends the extra pressure to there.

JC95Z

This is kinda what i was thinking. This is located in the rear quarter correct?

Injuneer

There's no solenoid.... there's a spring actuated valve. Sounds like the pressure relief valve may not be working.

http://shbox.com/1/evap_system.jpg

JC95Z

AWESOME. Thanks this will help alot.

WS Sick

Does the solonoid on the side of the intake manifold allow the fumes into the manifold or am I on the wrong track?

Injuneer

The solenoid on the side of the manifold allows engine vacuum to pull fresh air into the canister, pulling the trapped HC vapors from the charcoal. That is only activated under certain engine operating conditions. The pressure in the tank is "controlled" by the evaporative emissions control valve located between the tank and the canister. The canister is open to atmospheric pressure.

When the fuel tank is venting, the spring loaded valve between the tank and the canister opens and the vapor flows out of the tank, through the canister, where the HC's are absorbed, then the cleaned vent flows out of the canister. When the PCM opens the purge solenoid, air is pulled in through nozzle #2 on the canister (reference Shoebox's diagram), picks up the vapor from the canister, and it flows to the intake manifold.

WS Sick

I see, so the canister is the true vent and the manifold vacuume is there to dispence the waste (harmful fumes) from the canister.