I have been having a problem with a fuel vapor smell in the car. It is definitely coming from the rear of the car. Fuel hose replacement has been done in engine compartment. New tank filler neck gasket, etc. All hoses to the top of the tank have been inspected. No fittings busted off, etc. I have suspected my gas cap. PO broke the cap badly, but only broke the red shroud around the outside. I still suspected the cap. Roger sent me a used cap, and it is VERY different from my existing cap. Any input? The cap on the left is Roger's. The center piece is "non-vented and capped and is short and does not protrude past the shroud. My center piece is "vented" in appearance and stands up taller if you notice the side profile. I am wondering if mine is supposed to be capped like the one on the left.

 

They are both missing the rubber washer that can fall out very easy.

Thomas

 

I am by no means a cap expert but here are two caps I have, 1 from the GTS (left) and a spare from Mark Benton. Looks to me like your cap on the right got dropped and cracked the 'cap' portion of the inner piece. Maybe that gap is now allowing fumes to escape? Is there a lot of axial play between the inner and outer pieces? Perhaps you could just epoxy that seam closed?




Both of my caps centers poke out above the outer circumference, for whatever that's worth. My GTS cap has slightly more 'play' in it than the other. Dunno what that means. I never use the locking function, don't want to break that pawl thing in the lock mechanism.

 

Thomas,

Thank you for replying. Roger and I went round and round on the phone as to whether the cap requires a gasket. We have come to the conclusion that the gasket is on the filler neck. I have replaced that. I have yet to see a Shark cap with a seal in the cap.

 

Rob, thanks for those photos. Your photos are leading me to believe that mine should have had a center cap, and that it has broken away.

Let me ask this. Does you cap tighten down hard and tight when you put it on, or does it tighten up slightly, and then start clicking and slipping(pawl)?

 

I went and checked on my 88. It does have a black o-ring in the cap. I purchased it at Sharktoberfest from Tom at 928 Int. last year. I was having fun going around to others and checking to see if they had one. 99% did not. Check with them and let me know what you find out.
Thomas

 

Fuel smell at the back of the car is typically caused by a broken vent line.

I'd be surprised if an ill-fitting cap would be the cause.

While you figure out your cap issue, place something airtight in the fueling pipe and see if the vapor odours persist.

 

I have been cruising around with Roger's "test cap", and so far, no more fuel smell. My cap appears to have the center cap busted out of it, and it looks like vapor can travel up the center and escape where the red portion of the cap attaches to the white cap itself.

All of my vent lines and fittings have been inspected closely.

However, if this cap doesn't fix it, I will drop the tank and inspect again.

 

The cap should not be "vented". It is supposed to seal tight. I have two caps. Neither have obvious seals inside. BUT in my original cap, the center area IS taller than the outer wall, while in the used replacement I got from 928Intl when the original developed a crack, the center is NOT as tall as the outer wall, confirming what you reported. It appears there should be a similar height difference in the plastic lock housing that fits inside that center portion, but I can't confirm that. If Jim Bailey were still at 928Intl, we'd have the answer in 5 minutes. I swapped the locks, but I don't recall any issues. Perhaps I swapped just the lock guts.

PET only shows one cap PN for all year, and does show a separate seal (item 10 below) for all years. Usually when a part changes they will show an original PN and supercede PN when you click on the original part. Clearly, there are two different caps. The center is not involved in sealing. Not sure what to make of it, but I have had no problems with either cap. The first failed a smog cap sealing test and does have a visible crack in the center, so I got the replacement. I do wonder about the seal. It's not very expensive. [EDIT: Seal is on the end of the filler neck. See subsequent posts.]

 

Good lord, where did you go for smog that had an adapter for a 928 cap? My guy always unscrews the cap, looks at it for a sec, then screws it back on.

 

Thank you Bill Ball, that is the seal I am talking about. It is a easy part to to miss after laying the cap aside for fueling. I alway's check now. Get ready 928 int. for a run on cap seals.
Thomas

 

Item#10 is the seal for the filler neck and not the cap. The filler neck has the groove specifically for the cap seal. The cap tightens down on the seal effecting the seal. Not aware of a seal that sits in the cap - however I have been wrong before 8>).

Plenty of seals in stock for $7.69 each.

I am sure that the problem you are having is because of the smashed cap - let us know the long term outcome.

 

YES Agree!

 

Roger,
There is item 8 in the Bill ball diagram also which is some type of seal. I believe it is a o-ring. The cap seal I purchased for my 88 is a flat rubber seal that fits in the grove at the top inside of cap

Thomas

 

Its definitely going to leak vapor like that - it must be broken...

Alan