EDGE

I've been through my share of pumps. I've noticed a pressure release when I open the fuel cap, something I've never seen on any other car. Is this a normal thing for our cars? I'm wondering if this is leading to premature pump failures?

Twin_Turbo

iTrader: (25)

Yes but there's no way for us to judge if it's excessive so your only option is to check the white pressure valve, it's under the car, right side rear wheel. Near the rest of the fuel & vapor lines.

Even if there is excess pressure, it shouldn't lead to pump failures.

EDGE

I know the valve you speak of. If I blow hard enough, it will release. Not to the point my eyes are popping out of my head, but it does take a bit of effort. Is this a pressure release or an intake vent to avoid a vacuum in the tank?

Twin_Turbo

iTrader: (25)

pressure release and yours is working as it should.

EDGE

Thanks. I'm assuming the normal day to day pressure release is supposed to be through the Evap system up front? Is the whit valve an over pressure relief only?

Dark Ember

I need to make a writeup about this and post it in its own thread. I just corrected this(or at least it sounds like what I had on my own car). It was a bad ground on the purge solenoid circuit. Positive pressure builds up when that circuit fails. If the vent valve failed, then you would have negative pressure and you would hear that "hiss" noise when removing the gas cap, but you would not smell fuel vapors, since air was moving into the tank, and not out and into your nostrils. When I removed my gascap, I heard the "hiss" but it was positive pressure, and I could smell the vapors and feel them rushing out of the tank.
Get the engine up to operating temperature and disconnect the purge solenoid connector(its sitting on top of the charcoal canister.) Now connect a test light between the harness side of the connector. If the bulb does not illuminate, then you have the same problem i had, a bad ground at the back of the head. If it does then you have something else stopping engine vacuum from scavenging the tank pressure. I dont have long to go into more detail but soon I will post the write up and that will hopefully solve this problem for all 3rdgen owners for years to come.

Gumby

Yea something like that, it just keep the gas fumes from escaping.
and they can build quick from the sloushing around.

A non vented gas cap is part of the emission stuff but I can say it won't hurt anything if the pressure doesn't build like that. I use an approve gas cap with the hole/flap in it but just cause Im lazy. So I don't have to remove the cap to fill up. Just poke it through. but it don't woosh.

gas cap name brand
Clean-Fill
part # CF 701

chevy lovin

i have not found any one with a solution to the excessive pump failures and pressure problems. i think i finding out why god created carburaters. does anyone know what causes this? also replacing the gas tank did not work. no pressure in the tank and still smokes pumps.

Twin_Turbo

iTrader: (25)

What brand pumps do you use? Do you have the habit of running with an almost empty tank all the time?

chevy lovin

if your asking me. the tank is always 3 quaters or more.

95 4x4

iTrader: (1)

I also had some tank pressure an never could figure it out an once i did i could not believe it ! I replaced my OEM pump with a 195 Walbro awhile ago an recently started having pressure problems in the tank . I knew it had something to do with the venting . Pulled the pump out an looked at the vent line tube everything looked good BUT when you look from the underside their is a plastic cap that is snapped onto the vent tube . Their is a brass ball inside with a brass needle with a rubber tip attached an the rubber tip was stuck inside the vent it came off the needle so it shut off the venting to the CCP . The reason for this is for roll over's so the fuel stay's in the tank . All i did was take the rubber tip out an left everything else in place i have yet to have any pressure build up at all . Hope this helps you or some else out .

Gumby

Watch that CCP close, and change if its its old, mine was buring up ECMs in my car and took me 3 of them to figure it out. It shorts out internaly and fried the U15 chip in the ECM cauing other problems in the ECM when the board turns crispy in that area.

EDGE

Are you talking about the white valve under the car?

chevy lovin

i vented my gas cap today, and drove all over no howling or pressure. it was not 100 degrees today. it will be soon enough, and then i should know if heat has something to with it. it is hot in orlando almost every day.

ninetyone

iTrader: (2)

Ok, my car has a really loud wooosh!! after removing my gas cap. Also, the problem is this: After driving at WOT the throttle the car runs rough, and does not do the 1 to 2 shift smoothly. It runs great when cold, and actually runs awesome when it has say about 1/8th of a tank or lower. I have narrowed it down to a fuel problem and have replaced fuel injectors, fuel pressure regulator, diaphram, fuel filter. I may have a bad cap, but not sure yet. What do you think? only other things that i can think of is maybe bad canistor purge valve or that check valve by the gas tank. What do you think?