Hai gebissen

This morning I caved to the kids' pleas to take them to school in the 928. When I got home from that 4 mile journey, I popped the hood to check the oil level. Looks like I may be consuming a bit, but quickly shifted to another problem...the strange dull popping noise every 5 seconds or so from the rear or the car. I opened the hatch, and looked at the top of the fuel level sender, and saw what looked like the fuel tank falling out of the car! I then looked under the car and saw that the tank was collapsing badly. I vented the fuel cap (whoosh) but the tank is still badly deformed. I hope my brand new level sender isn't damaged.

I had noticed during Frenzy that my fuel gauge was erratic at times...now I know why.

Last week I replaced a broken Y in the right front wheel well at the charcoal canister (factory part). Prior to that it was obviously open to atmosphere. I have now made the system "functional" to reveal another issue. This car sat for several years, so something is likely blocked in the vent line back to the tank I would guess. I see by searching this forum that collapsing fuel tanks are not that uncommon on these cars.

Hai gebissen

^sitting considerably lower than normal

Rob Edwards

You probably saw it already, but I had a good fight with imploding gas tanks about 3 years ago. Ended up being a faulty tank vent solenoid that failed open, allowing manifold vacuum to implode the fuel tank.

https://rennlist.com/forums/928-foru...el-sender.html

If you have already verified that all the vent pipes and hoses aren't kinked or obstructed, then this is the next place to look, after re-inflating the tank.

jeff spahn

Damn Rob. I was going to suggest to this guy that very same explanation . . . .after you had explained it to me the other day on the phone. Quick on the draw.

Hai gebissen

I did see your thread from 2010, thank you. The car is in my driveway and still runs, so I am going to leave the fuel cap off and drive it to the shop (12 miles) where I have compressed air etc. and deal with it there. I also unplugged the vent solenoid electrical connector.

newworld

87s4 aut.

these fuel vapor emissions setups can be a headache as cars age. porsche uses valves in the lines, and i have other porsches of this generation and my simple solution on the 928s4 was to put in new hoses and y connector in the fenderwell, and then block it. i was getting fuel smells there.

my car had the air pump removed, so what i do is leave the fuel filler cap slightly ajar to vent....

FredR

You guys have just reminded me of something that happened a few months ago- my vent line snapped [the rubber was petrified] just in front of the motor so I [temporarily] placed the open connection such that it now vents inside the engine bay.

Duly forgot all about this- not sure if it is a dangerous condition- highly unlikely the vent pipe will catch fire from the fumes emitted but something that needs sorting.

Regarding the OP problem as I understand it is designed to vent tank pressure back to the inlet manifold via that actuated diaphragm thingy at the front of the vee. I am not sure how that system is intended to work but presumably the last thing we need is engine vacuum evacuating the fuel tank. I have assumed that valve closes if there is more than a minimal amount of vacuum and opens when the engine is cruising type of thing so as to allow the tank to breath wthout collapsing it. If that valve sticks open presumably that is what causes the problem?

If anyone can explain this sub system in more detail much appreciated as doubtless will the OP.

Regards

Fred

Hai gebissen

Probably just found and fixed the problem here in my driveway...using Rob's thread, I went to look for the vent tube end behind the rear bumper. I found it...a metal tube pointing straight down, perfectly blocked with dirt. It has been that way since I got the car in May, but it wasn't an issue until I replaced the broken plastic Y piece at the charcoal canister (and closed the system).

Is there supposed to be some kind of screened cap or something on the end of this pipe?

I'll take it to work tomorrow and gently pop the tank back into shape with compressed air.

Leon Speed

The vent line is supposed to have a rubber flange thingy on the end, not sure of functionality, maybe to get more air in or to steady air flow around the pipe end.

Hai gebissen

I see. Anybody have a picture? Maybe it is also to keep dirt out...

gearz

Don't have a pic but there should be a funnel shaped rubber "thingy" at the end of the metal vent line. PET calls the part 'end piece' - 928 201 195 02 - can't be more than a few bucks. I would suggest replacing it as I'm sure it's designed to help prevent the vent line from being obstructed.

Hai gebissen

Thanks for the part number. It is $4.50 according to Pelican.

The end of my line looked like someone jammed it straight down into the dirt. It probably happened when the car was towed with no rear bumper cover.

The tank didn't rebound on its own after being out in the fairly warm sun today. I'll give it some air tomorrow at the shop.

Earl Gillstrom

I have a spare tank if you need one.

Earl

Hai gebissen

Thanks. I am hopeful the compressed air technique will do the trick. It really imploded. The bottom looks very much like Rob's did in his pictures.

Mrmerlin

make sure to replace the electric purge valve as well,
the blocked line shouldn't be enough to suck the tank closed
NOTE you will get a couple of events before the tank cracks.