Since someone just posted a good pic of our evap lines, I thought I'd start a thread that ties in a few very informative threads (Terry and Matt D) with a very common and annoying CEL. Please post if you have anything to add.

CEL 31 supposedly occurs when the EVAP system sees positive pressure and a membrane ruptures.

Terry has mentioned that this is not due to the rollover valve, which is located between the tank and the chassis http://forums.2gnt.com/dcboard.php?az=show_topic&forum=4&topic_id=95658&mode=full

There is another membrane between the spare tire and gas tank that ruptures:
http://forums.2gnt.com/dcboard.php?az=show_topic&forum=5&topic_id=93653&mode=full
&
http://forums.2gnt.com/dcboard.php?az=show_topic&forum=5&topic_id=63598&mode=full


A one way check valve is an easy and cheap preventive measure. When you are boosting, which line should have the check valve to avoid the Evap code? A or B or C?



Sounds like it's line B
http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=75347&mode=full

Boost pressure will not damage any evap equipment Erik. The only concern was the Rollover valve and proved that its not possible. Like I said before, i have boosted mine to 30psi and never damaged anything. Its been proven, period.

The main key is to keep all the rubber lines in good shape. The rollover valve clearance issue could be fixed with a hammer if you wanted to dent the bottom of your car.

The rubber lines are notorious for developing dry rot cracks, I have seen that many times on both my cars and other people's cars.

Gas cap has been known to fail in the vent.

The rubber diapgram you refer to in the rear of the gas tank is the fuel FILLER NECK. Its a rubber hose just like a radiator hose. You can develop leaks if a clamp fails or the hose dry rots.

Also, the pictures Terry posted of the valve, have been put into a wiki article.

Originally posted by Star Turbo Talon
The rubber diapgram you refer to in the rear of the gas tank is the fuel FILLER NECK.

Terry, I know I'm reiterating here, but to quote Matt from the thread I linked "Well I know for a fact, at least for the turbo guys, that this CEL is caused by a valve right between the gas tank, and the spare tire well , under the car. There is a rubber diaphram inside it, and can tear if it sees boost pressure. In the center of this diaphram, is a plastic pole piece, with sharp edges on it, on the underside of it, and if boost pressure gets in it, can tear the diaphram on those edges."

That doesn't sound like a filler neck, he keeps referring to a diaphram.

I know you disagree strongly with the theory, but considering I have never seen it with my own eyes, I have to go by the evidence:

A)RUBBER diaphram (per Matt), which can be exposed to:
B)boost pressure, via the EVAP lines

A+B=potential failure point. A $1.30 one way stop valve seems like a good idea

ha ha odd time for this to pop up, but the canister on the passenger side, like right inside the bumper is ticking? any fixes?

not the canister. thats either the Leak detection pump or the Evap solinoid. Check your codes. Repair is to replace it.

http://www.2gnt.com/index.php?d=Roll%20Over%20Valve%20Boost%20Myth%20-%20BUSTED!