CheVelleSS

iTrader: (1)

Ive noticed everytime I go to the gas station and start to pull the gas cap, it always has alot of pressure behind it. Like if I take it off real fast it will blow the cap off in my hand.

Is this normal? Ive never had another car that did this. I will try to get a video of it next time I fill up.

Kalogerus

iTrader: (3)

There is a caution written next to the cap about this. Yes, this is normal.

eknine9

iTrader: (8)

Completely normal, and totally cool IMO. I love the odd time when someone happens to notice an they get to talking about my car.

klobb92

Haha i was always wondering about that!!

MooJohn

There is supposed to be a couple of psi (like 2-3) pressure within the tank. Anything more and it is an issue and can break things, including blowing the tank. You can find pics on here of bulging tanks due to a clogged vent. That's some serious pressure, far more than I would want in my car.

The vent line on my tank leading to the canister under the hood is totally blocked with rust & crud. That's ok because the line itself is also blocked somewhere along the way. The only fix for this will be to replace the tank and run a new line (I plan to use rubber fuel hose) up to the canister. In the meantime I leave the filler cap loose so fuel pressure isn't affected by the tank pressure.

INTIMAZY

iTrader: (5)

Is it actually pressure? Or is it vacuum??

I always thought it was vacuum and the noise was air rushing in, not out. Where would the pressure come from anyway???

MooJohn

Expansion of the fuel I suppose. You would think there would be vac created as the fuel is used but I promise it's pressure, and it builds up quickly when there is no way to vent it. Obviously it's a bigger problem in summer months, esp when the temp is in the upper 90s or more.

I've seen pics around here of someone's tank that was all puffed up and expanded from the pressure. Filling the trunk with atomized fuel and vapors while you're driving is not something you want to experience.

The vent line leaves the tank under the car near the driver's side rear tire. There is a short piece of rubber hose that connects the tank's metal line to the metal line leading to the front of the car and the charcoal canister. I connected here and found that the line in both directions on my car is totally clogged - it held full shop air pressure without blowing anything loose.

Lokz

iTrader: (1)

its vaporized fuel that escapes from the tank when you open it. Its stored in the EVAP system and waiting to get used for combustion. When you open the tank it all escapes. Some cars have caps which let these gases escape when gone over certain pressure so it doesnt blow **** up. I hope this helped you guys. Cheers!

t2d2

iTrader: (8)

Is there only one part-rubber line from the tank by the left rear wheel? I felt around and could only locate one such line, but it was tough to follow stuff above the suspension without the car raised up. The rubber was rock hard, as would be expected after 20 years. I'd like to try getting that off to see if I have a similar blockage problem...

How far up does the rubber hose go before connecting to the tank's metal line? And aside from obvious emissions issues (assuming my charcoal canister is still any good, anyway), would there be any harm in disconnecting the rubber hose to see if that allows the tank to vent properly? I think I have excessive pressure (gas pours out when I open the filler cap with a nearly full tank) and would like to eliminate vent blockage as a culprit before digging deeper into leaky injector bypass possibilities.

Of course, if my tank vent itself is rusted like your's, there wouldn't be any way of knowing if it's venting, right? Did you determine that by draining the tank and trying to blow air through the vent? FI-61 in the service manual is all I could find about that system, and it doesn't go into much detail about how the vent system works. I would have thought a vent has to be on the top... How does it allow air through but not fuel??

t2d2

iTrader: (8)

Hmm, I may need more pointers on which line to look for from the tank vent. It looks like all of the metal lines behind the fuel filter (toward the trunk) slip into some rubber-like sleeve that may in fact be metal -- it's so hard, it's tough to tell what the material is. I've got the front of the car up on ramps right now and was able to gain a bit of room to look back there, but I still can't follow the fuel lines to see what goes where without jacking the rear end and hopefully gaining some sight lines.

I did pull the charcoal canister and run through the tests and "cleaning" (via blowing compressed air into one of the ports while covering another) and it seemed to be okay. I had a little bit of air going the wrong way out of the check valve, but I was probably exceeding the pressure it's rated for. BTW, the service manual doesn't mention having to remove the hose clamp in the wheel well to get the canister removed!

OUChase

I fear I'm going through the same thing. Did you ever get it resolved?

scRuss

i believe if you dont have any pressure you need a new gas cap.
Just my opinion

t2d2

iTrader: (8)

Nope! I tried a few other things to no avail, but I haven't tried following the lines from the tank under the car yet.

Uh, did you even read the thread? The discussion was about too much pressure.

scRuss

well i dont want to argue but he asked if alot of pressure was bad.. so i saaaiiid if you didnt have pressure yous need a new gas cap...
Pressure is normal btw

SC400slide

iTrader: (11)

Good to hear it's orthodox. My 95 hisses like a snake when I remove the cap...