Ok, ever since I picked the car up from the mechanic.. lol... anyway, here's my problem.

I shut off the car, suddenly I hear a big "gas release" sound coming from the area of my gas tank.

Then I'm sitting in the driver's seat, I start hearing rumbles that sound like they're coming from the gas tank. It sounds like there is air trying to escape, causing bangs and ****.

My response to these 2 problems, start the car up again. I start it up, and the revs go insane, up and down, up and down, like crazyness. So I shut it off, call my mechanic, explain the problem.

He says "open the gas cap and let the pressure out". So I do it, and it starts normally.

HOWEVER, I still here the gas vapours whenever I shut my car off. It's like, I reverse into my parking spot, shut the car off, and 2 seconds later, it's like the sound of vapour releasing coming from the back of my car. It's like "PSSSSSSSSHHHHH!".

And every once in a while I steal feel the gas in my gas tank rumbling when I shut the car off. Any ideas? Tell me it isn't the fuel pump about to go... PLEASE TELL ME IT ISN'T THAT!!!!

 

Drop about half a dozen Rolaids into the tank next time you buy fuel and get a new gas cap at Crap Tyre.

 

Yeah.. I hope its just a leaky gas cap.. or you could have my problem.. the fillerneck breaking from the tank, but I think there is a recall for you gas tank, but not mine..

 

my gas cap isn't leaky, i know that for a fact.

cuz well, it works fine. when i tighten it it's firm as hell, it's one of those lock ones too with the key.

when i undo it, i feel the pressure come out.

 

well I dunno man... is it hissing by the gas tank? your filler neck maybe starting to brake the solder at th ejoint to the tank... Take a hard right corner.. if you smell gas pretty bad.. thats whats happening...

And I know what you are thinking... "but my car is mint, with no rust underneath, it can't be that" well, my car is rust free underneath as well, its not rust, its gay *** design by GM mother fockers

 

Easyspeed it's not having a leaky cap that's the problem. The tank builds up presure if it's not venting. I'm fairly sure It's the cap that has the vent in it and there's no other separate vent system for the tank.

Edit - so what I'm saying is change the cap because maybe the vent is plugged and if the vent isn't in the cap find out where it is and check that.

 

the cap has a vent in it? impossible.

cuz no air is coming out of the cap!!!!! hehe

i can tell you one thing, vapours are definitely building up in my gas tank...

 

It has to vent somewhere and you may be right about the cap - now that I think about it maybe it vents to some emissions cannister or something but either way it sounds like it's not venting properly.

 

Yes.. there is a vacuum line going from the charcoal canister in the front to the tank.... you should never hear hissing

 

I dont wanna sound rude, but everytime I read one of your post, something is wrong with your car... it reminds me of me when I first got my car. whats this? whats that?
hahaha good times

 

Hey EasySpeed sorry to hear about your troubles.

I think my Formula has less Ks than your Z and for what it is worth I've had it for a year and a half and it still has issues that I am ironing out. Mostly stuff that happens to 12 year old cars that spend all their time sitting in a garage.

About your tank burbles, some of it is normal like if it goes from cold to hot (ambient temp) and the tank is below 1/2 say about 1/4, we have baffled tanks (91 and up) that have that effect -- they take some time to purge. The fuel pressure purge takes a little while to catch up under normal conditions and when you turn off the car it does a full system, immediate purge. If the system has a problem it can be easily checked but if I were you I'd go to GM for that not that they know squat about TPIs (let me tell you stories about that) but they do have equipment and alot of experience on GM fuel/evaporator purge systems.

If it is the fuel evaporator system then the car's driveability will just get worse it won't die on you.

adious,
RP.

 

The gas cap does not vent. Ther is a separate line going from your tank to the charcoal canister, this is your vent line. Where the two fuel lines(feed and return) run along the frame in the engine bay, there is a third line beside it. This line goes to the charcoal canister. My best guess is that this line is plugged somewhere in between your canister and your tank. Get it fixed. Having your tank explode from excess pressure build up would really suck. The pressure might blow out a weld or something.

 

Last I heard the excess pressure in our fuel tanks is normal. I've always been told that it's a good sign if you hear a hiss when you release the gas cap, although I'm not sure if the tank pressure is high or low. The rumbling from the gas tank kinda sounds like the fuel boiling due to the muffler being right under the tank, which I've also heard happens on occasion. My GTA does both and it runs fine...

 

That makes COMPLETE sense in my mind. Maybe try disconnecting the line to the cannister for a short ride and see if it fixes it.
greg

 

I am pretty sure that hiss is a vacuum. My gta has a heat shield above the muffler... Dunno if that is standard on all years or not though.
greg

 

Now that I think about it my heat shield very well may be missing. One of the previous owners had some sort of aftercat exhaust installed so the heat shield may have been tampered with. Not that it matters; the little 305 sure sounds great.

Hey cool, my 300th post. Hear that Mr. Shields? I'm catching up...

 

#1) You do not have a pressure buildup by the tank not venting correctly- just the opposite- you are creating a vacuum in the tank- thus the 'pressure release' which is not pressure- it is air being sucked INTO the tank. The proof it is a vacuum- not pressure- buildup is in the fact you had to open gas cap to get car to start- the vacuum was too great for the fuel pump to overcome.

#2) Gasoline is extremely unstable (i.e. shifts between liquid and gaseous state occur relatively quickly in normal ambient air temperatures)- and the Reid Vapour Pressure specs. allowed by Transport Canada for the refineries make it worse (way too high). The 'noises' you are hearing when car is shut off (except the hissing/suction sound) are the tank walls expanding and contracting as gasoline changes states- with no venting the change in density pulls and pushes on the walls and they are thin enough to flex quite a bit.

#3) You will not 'blow' the tank- i.e. BOOM- if gasoline expands enough that the fuel tank assembly (everything) cannot hold the pressure (i.e. once engine is shut off and extremely warm weather hits with a tank that's 1/2 empty)- the weakest part-i.e. could be the tank seams or maybe the gas cap, or maybe the fuel pump mount, or maybe the filler neck weld- whatever- will 'pop' off- it is extremely unlikely that this in itself would cause any sort of ignition and start a fire. What is more likely is that it will pop somewhere and allow gas to leak out on the ground where some careless nimrod will throw a burning cigarette butt.

-You need to determine where the vent system is plugged and get it repaired. Driving it around is not a good plan as eventually you will cause another problem (i.e. blown fuel pump) and still have to fix the venting issue. For right now to move it around- the best idea would be to keep the fuel tank as full as possible at all times so that fuel pump hasn't much existing/created vacuum to work against.

 

Thx for the lesson very interesting read. Curious, not always but sometimes when my tank is low say about 1/8th and I let the cap off it does vent outwards stinks of fuel I can feel the hot vapour blowing out from around the cap. Is this normal ?

RP.

 

Normal? Not really- although if it's only a slight pressure buildup once in a blue moon on a very hot day- it happens. Seeing as how I don't know your setup-remember that carb'd vehicles need a vented gas cap, FI vehicles typically do not. If this happens regularly you more than likely have a small restriction somewhere- although if this happens immediately after shutting engine off and you were idling for an extended period of time previous to this- the fuel return line from engine may help to pressurize tank on either a carb. or FI setup (i.e. alot of unused fuel/vapours being sent back to tank) and it's not so significant. Not trying to be obtuse on this- but it is a 'problem' the question is major or minor- depends on frequency of occurance and conditions surrounding it- although someday you may have to look into it.

 

Thx for the notes. I think I won't worry about it -- it only happened in high summer when I let the tank run down to fumes, maybe once or twice thats it.

RP.