So 87 924S when I fill up I get a gas smell until the level goes down some, so looking at the PET 201-03 it shows several hoses and the main filler hose. So can all the smaller hoses be replace with straight hose? It looks like it will also need a short section of filler hose that is much bigger.
I am getting ready to replace the sun roof gears so will have all the carpet and trim pieces removed and would like to replace as many hoses as possible.
Dan

 

The most common problem with the early 944s and the 924S is the metal gas tank cracking at the top. If you search you should find discussions of this problem. I dropped my tank and had it welded at a radiator shop, then replaced the hoses.

 

Agree with Elgy, I had the same problem with my 84 a few years back. Ended up finding another good used tank and had it professionally repaired prior to reinstallation.

 

Can you see the crack with the tank in the car? What a bummer, I had the transaxle and rear suspension out in December, I did put in a new screen in the tank and fixed/cleaned the sending unit now I have to do it all again !!!

 

The source of my smell was the filler neck itself. Mine was a late model version which is made of plastic (as opposed to the metal early model version). I replaced with the early model metal filler neck (and sleeve) and have had no issues.

But yes, could also be the breather lines or the tank itself

 

I found the smell in my case was coming from the drain on the rubber around the filler tube. Really bad after a fill but slowly went away. Didn't discover this was the issue until after a lot of rain and noticed water in the wheel wells. Fixed the rubber tit that held the drain hose and that also fixed the fuel smell. That drain was supposed to tie into the sunroof drain and funnel water & fuel down and away from fuel fill, but without hose attached, dumped it in the wheel well. I modified the pressure relief valve on the system (under metal cover by fill tube) close to the same time to stop the pressure in the tank from cycling and causing (or helping) the tank to crack.

 

MORE INFO, got home tonight, and about fifteen minutes later went to look at filler tube, opened cap and got the big whoosh of air so that should rule out a cracked tank??

 

I would think so yes.

Typically when you have too much positive or negative pressure in the tank its related to an issue with the EVAP system not venting properly. Could be a separate issue, or possibly related. Youll have to do some research on the system and some diagnosis. Simplistically speaking, theres a line that runs from the tank to the engine bay, which connects to a purge valve. When car not in operation or when engine is cold, the purge valve sends tank fumes to the charcoal canister and then (I believe) to atmosphere. When warm, a thermo switch opens causing vacuum to active the purge valve which then pushes/redirects tank fumes (and charcoal canister fumes) into the intake.

A google image search of the Porsche 944 evap system should reveal plenty of diagrams to help you diagnose through the use of some lightly pressurized air to see if there is a blockage. You might want to look at the charcoal canister or lines running to it to determine if you have a blockage causing too much vacuum/pressure in your fuel tank. As you may have noticed with any 5 gallon gas tank, heat can cause fumes to expand/contract and needs to have a vent to equalize.

I have found diagnosing the source of gas fumes is very difficult due to the number of different potential sources and difficulty in reaching them. Fuel neck return lines, fuel filler neck, expansion tank, fuel level sending unit gasket, tank itself, evap system lines, pump/filter lines can all be sources.

 

Charcoal canister usually connects to the intake manifold and when the engine is started cold the purge valve opens and fumes are sucked into the engine. The whole reason for an evap system is to keep the fumes from getting into the atmosphere.

I was just going to say my 83 did this yesterday at the gas station so that means my system is sealed - and probably my purge valve is stuck closed. :-/

 

The charcoal canister absorbs the gasoline fumes before venting to atmosphere. When the purge valve is closed the excess pressure in the tank pushes/vents through the canister and out to atmosphere. When purge valve is open, intake vaccum sucks from canister into the intake. My understanding is the charcoal serves the purpose of absorbing and cleaning the air coming from the tank (for emissions reasons) before venting. The thermo switch on the head opens when a certain temp is reached, allowing a vacuum which triggers the purge valve(s) causing the purge valve to open (as you can see there are actually two valves which run in sequence). Purge valve opens, allowing vacuum from intake to suck trapped fumes from the charcoal canister which have been building up when the car is sitting.

The tank needs to vent somehow or the pressure/vacuum will build up too high, just like the gas can in your garage. It cant be a 100% closed system.



Heres another useful diagram (Line 30 in the above diagram isnt shown well on this diagram, but it is part of/connected to the roll over valve #4, 31 in above diagram) - I think there are also some variances between early and late model cars EVAP systems as well so these diagrams might differ between models. Most of my knowledge comes from a late model system

Flushing air line = atmosphere

 

Your system is indeed sealed. If it was sucking in, the one-way valve is stuck. If it was blowing out, it is doing it's job. As the fuel depletes, the valve lets air backfill into the tank through the canister. If the fuel vapor pressure gets above atmospheric, it holds it in unless it exceeds 2psi, then it vents through the canister. The fuel can get quite warm with engine waste heat flowing under the car.