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emoore924 · Joined: 13 Apr 2004 Posts: 2815

Ok, that's what happens when I remove my fuel cap after a stint of hard driving. There is considerable pressure within the tank, so much so that if I don't hold onto the cap tight when I'm removing it, it would blow right out of my hands. This outgassing continues on for about 15 seconds at a decreasing rate (almost sounds like the fuel is boiling in the tank when the pressure is released...). Also, not sure of the relevance of this fact but the last time it did this, the engine died immediately when I removed the cap. I can also hear the fuel tank going ka-thunk! as it pops back into shape once the pressure is relieved. It happens every time if the car is hot when driven hard. So, not an intermitant problem, and it has been doing same more or less for years...

1979 n/a. Runs fine. Fuel pump is starting to make a little noise however, but I'm not sure that has anything to do with this. Might be a simple coincidence.

Ok, so why so much internal pressure within the fuel system and tank? Is this normal or not?

If not, what do I need to do to remedy?

DOCO · Posted: Thu Oct 23, 2008 3:39 am Post subject:

tank vent is plugged most cars vent through the gas cap.not really sure about the porsche though .gures please
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Doco "where am i going and why am i in this handbasket"author unknown
79 924 N/A "Webster"
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fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Your tank vent is plugged. If left to go for too long, it could collapse the tank.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

Smoothie · Posted: Thu Oct 23, 2008 3:54 am Post subject:

Sounds severe.
I'd check the EEC system. It's shown in the Haynes. There's a safety valve that should open at a certain level to relieve pressure from the tank. That flow from the pressure relief should go forward to the charcoal canister or to the engine when it's running and warmed-up and at part throttle. -So there are a few components there to check, but my prime suspect would be the safety valve - it may be stuck shut (, but don't ask me where it is). Another possibility would be the charcoal canister vent being clogged, but then the pressure should still be getting relieved when the EEC control valve opens (when running, warmed and at part throttle).
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

ideola · Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI

Ed, once you identify the problem, if it can't be repaired, I may have spares of the components you need...let me know.
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erstwhile owner of just about every 924 variant ever made

emoore924 · Joined: 13 Apr 2004 Posts: 2815

EEC = ??

!tom · Posted: Thu Oct 23, 2008 5:07 am Post subject:

Evaporative Emissions Control
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78 924 NA
5-lug

Brockoli · Posted: Thu Oct 23, 2008 5:10 am Post subject:

EEC = evaporative emission control

its a system that sends gas tank fumes+crank case fumes to your air box to be burnt in the engine.

Do all 924's have this much pressure in the gas tank. Mine does this too, but at the last couple fills it hasnt. Mine doesnt make the gas tank deform tho.
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emoore924 · Joined: 13 Apr 2004 Posts: 2815

EEC, got it.

I think the problem might be that the EEC pressure relief valve only operates when the car is warmed up and at PARTIAL THROTTLE.

I only operate the car at FULL THROTTLE

I'll check it out...

Ozzie · Posted: Thu Oct 23, 2008 7:14 am Post subject:

Not sure if its the same for US cars but there is pressure valves next to the filler hose on mine. Have to remove the cover on the RH side for access.
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Smoothie · Posted: Thu Oct 23, 2008 10:33 am Post subject:

924guy · Posted: Thu Oct 23, 2008 1:02 pm Post subject:

try looking at p/n 810201106a "bleeder valve", there is also a "shutoff valve" which looks very similar, in the same assembly. should be located in , or near the fuel delivery pipe housing, attached inline to vent hoses. if this, or its equivelent is blocked or missing, it will cause the problem you describe. looks like an oversized vacuum valve (acorn.)
I can take a picture of a real one if you need, but its in the 84' 944..earlier may or may not be different, and i for some reason i cant snip a pic from adobe pdf's anymore, guess id better install the full version again..
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78 924
82 931 SE "smokey"
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ideola · Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI

Joes924Racer · Posted: Fri Oct 24, 2008 3:42 am Post subject:

I though on the early cars there was a vent built in the the filler neck that runs from the tank to the gas door connected with a rubber boot and clamps off the neck runes a vent line... am i right.
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gwan2cruz · Joined: 26 Nov 2017 Posts: 18 Location: Lima, NY

My 1978 924 is a n/a engine and I am having the same problem with lots of pressure when I remove the gas cap after driving. I know the bleeder valve is no longer available so can I just remove the valve and put in a direct line to the canister?
Thank you.
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78 924 Special Edition