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Gas smell in cabin when stopping


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On my 2000 S I've got a situation where if I intentionally stop quickly I will get a smell of gasoline inside the passenger cabin that clears rapidly if the windows are down. It seems to be worse when there is less gas in the tank so it would seem to be related to sloshing. If I stop slowly there is no noticeable odor and the problem is definitely repeatable.

So far I have replaced the fuel tank top sealing ring (no change) and pulled the wheel liner (no obvious spots that are leaking but there is a bit of gas odor.) All of the lines look like they are in good shape. There are no codes other than what were related to a recent AOS replacement. I recently filled up the tank so the problem is harder to reproduce right now and by the time I get stopped and out of the car to check the wheel well area there's no real odor left.

I'm trying to avoid just throwing money at the problem or else I'd take it to the dealer. Hopefully I can get a few suggestions as to the most likely causes and/or things to check so the problem can be approached in a more methodical manner.

Edited by Tom M
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One additional piece of information is that after doing some testing I did pick up some odor by the vent valve at the top of the fuel filler tube. When I removed the gas cap some gas wicked out via what looks like a very small vent hole. Any odor associated with that seepage would obviously be trapped by the cap but if the vent valve is bad then I guess that could explain it.

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As mentioned, no active codes.. I do have a P0507 - Idle Air Control System RPM Higher Than Expected that is shown as pending. I had just started the car so I'm not worried about it at the moment. I cleared the codes related to the AOS prior to doing the replacement and they have not returned.

The cap seal does have some light cracking on one portion so I'll replace it when I order any other parts but there is zero odor coming from the cap area when it's in place based on sticking my nose down there - even when there was odor detected under the wheel well.

Edited by Tom M
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I don't drive the car that often at the moment but do not believe there to be a true leak anywhere as I think it would be more evident than only when stopping hard. A cursory inspection of the lines was made and they look OK. However when I do smell it under the wheel well it's difficult to locate the exact spot as the tire's pretty much in the way even when turned. I have noticed the smell as low as the bottom of the canister and as high as the valve. With the wheel off I can't locate any place that has an obvious evidence of leaking, which means it's probably only vapor that's getting out.

I'll pull the wheel again and see if I can find anything else. What I really need is an electronic gas sniffer.

UPDATE: After pulling the wheel and getting up close and personal it smells like it's coming from either the area of the valve (both connections move freely) of from the area of the canister. However the canister may just be because of trapped fumes located behind it. In both cases there is no trace evidence that anything is leaking.

Edited by Tom M
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Could it be the valve that shuts the EVAP canister off from venting?

I have a spare EVAP canister shut-off valve 996-605-201-01. Left over when I thought it was faulty, but it tested fine. http://www.renntech.org/forums/topic/41644-evap-canister-valve/

I can send it to you for whatever the cost of shipping is, $5? If it fixes your problem, send me an additional $30 (list is $112.81?). If not, just send the part back and not only will you have eliminated that as a problem but you'll only be out ~$10 for shipping both ways.

Again, don't know if this'll fix your problem.

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Thanks. I'll definitely keep that in mind.

I started the car and smelled around but couldn't locate anything exact. What did seem a bit odd was that one of the valves on the top of the canister seemed to by cycling about 5 times per second. I have no idea if that's normal or not but the car had only been running for about 20 seconds prior.

I also got a whiff from one of the lines running along the top of the fender where it's clipped into place but it looked OK. I'm hesitant to just start unhooking vent lines and doing detailed inspections as things are more likely to break since the lines will have aged quite a bit.

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More test results. I started the car and just let it idle while I went around and did the sniff test. Initially there was no noise from the solenoid/valve but there was a gas odor between the vent valve and the canister. It seemed stronger at the orange connection of the vent valve. After a while the solenoid noise started up so I guess it's normal and perhaps it depends on the tank pressure. The fact that the odor is between the valve and the canister may just be due to the gas fumes drifting down due to their weight.

At this point I'm not sure what other tests to run unless I can somehow isolate the vent valve to confirm it is or isn't the culprit.

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Loren, I take it those faults won't throw a code since I don't have any current/pending codes showing? Having the dealer run the test will cost more than just ordering the part so that's out. I'll check around to see if there's anybody local that may have something which can be used.

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  • 2 weeks later...

I broke down and bought a combustible gas detector and as far as I can tell it appears to be leaking from the top portion of where the filler tube enters the tank. How often does this fail? Also, how does the filler tube seat at the tank and how difficult is it to replace? The shop manual shows it's a 7 step process and that it's just a twist fit so it sounds like it could be a DIY. There's a new filler tube on eBay but the revision number is higher that what I've got in my PET version.

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I've got a pending order with Sunset of all the ancillary parts I need after dis-assembly and now that I (hopefully) know what the problem is I'll call them in the morning to get a price.

Do you know how difficult the job really is or is it truly as simple as the manual makes it sound?

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  • Admin

Porsche Book Time is 1.4 hours total - so it seems not too tough.

Pretty much remove the wheel and wheel liner to get access. Then it should all be in front of you.

Might be best to run the fuel tank down pretty low and make sure you are in a well ventilated area with no spark sources.

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I called Sunset and based on my VIN they say I need 996.201.043.07 @ $305 vs. 996.201.043.09 @ 219. Apparently the -07 is for cars equipped with the OBDII. Does this make any sense? Should I be able to reuse the component off my existing setup?

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  • Admin

Hmm... and your car comes up as an "S" in their system?

I guess that is required because of US EPA laws (anti-vapor leak test).

It all comes down to where the leak is... the valve, gasket, and washer are all available separately.

Do you see any problems (cracks, signs of leakage) with the filler tube itself?

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I don't have the filler tube out yet as I need to use up most of the fuel in the tank in order to remove it. However since the leak seems to be where it joins the tank I would guess I really only need a new gasket & maybe a new support washer (996.201.753.00 & 996.201.755.00). I just hate to order too little and wind up needing to order more parts. Perhaps I'll wait until I get the fuel level down and pull the tube before deciding what to do.

How difficult is it to remove all the vent lines as they look pretty stiff and may be difficult to reuse. Would it be best for these to be ordered as well?

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  • Admin

Well that is the problem on a 12 year old car -- you never know if the plastic parts have become brittle or the rubber parts are cracked and dried out until you look or move them.

Unless the car has been in an accident or the filler tube damaged somehow I do not see how it could be bad - but then again inspection is needed.

I do not know if Sunset will let you return unused parts (still in their bag/packaging) or not. Might be a good question for them - talk to Bob McCarthy and tell him I sent you.

Always best to have all the parts you might need on hand...

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Just got done placing the order including new rivets, plastic nuts, gas cap, gasket & washer. The latter 2 need to be ordered (3-4 days wait) so hopefully I can get this fixed early next week. It would cost almost as much to return the washer & gasket as to toss them out ($6.81 each) so I'm not going to worry about it. As far as the vent tubing goes, if I need new I'll buy some correctly rated stuff locally as the official parts are $50+ each. I'll just be careful during the removal process. :)

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  • 1 month later...

I finally got around to replacing the gasket & washer on the fuel filler neck. The process was fairly easy and I managed to do it w/o taking off any of the lines be removing the one valve clamped to the neck. After getting it replaced and buttoning everything up I took it for a test drive and discovered the problem still exists. :(

So, for now at least, I'm at a loss as to the actual source of the problem. I've replaced both tank gaskets so that either leaves a small leak in the tank itself, one of the pieces of tubing or one of the valves. Since it's not the end of the world it's going to have to wait to get repaired - probably at the dealer.

Again, the odd thing is that it really only happens when stopping hard and making the fuel int the tank slosh around.

Edited by Tom M
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