924Board.org

[D Hook]

Okay, so Tom Cooper came over and we changed out the hose from the tank pump to the external pump. When we pulled the hose off the in tank pump, not a drop of fuel came out. We added a little gas to the tank to see if it would flow just that much and nothing...nada...zip. So obviously, there's something in the tank restricting the flow, maybe, as someone suggested, the liner has peeled off the inside of the tank. (Had a liner put in back in 2002.)

So we attached a new 1/2" hose (that fit nice and snug) to close the system and it was getting late but decided to try one more thing. We hooked up an air nozzle to the hose coming off the tank and removed the gas cap and blew a shot of air (about 40 PSI) into the hose, hoping to it would blow away any crap from the in tank filter. It did. A lot of gurgling from the tank and in a second, fuel started pouring out freely. So we reconnected the hose and cycled the pump a couple times and it filled up the clear "filter" (which actually isn't a filter, we found; more on that) and the car fired right up after filling the fuel lines.

So there's schmutz in the tank, blocking the flow. Either rust (doubtful) or some of the liner has peeled off the side of the tank and is blocking the in tank pump filter. I'll need to pull the fuel gauge sender and see what's in there for sure. But I need to burn off almost a full tank of fuel first. I don't think it's rust or debris because when you look at the "silencer", there's nothing showing up in there that we could see. No sediment, no particles. But I'll check the clear silencer in the morning 'cause if it's pumping sediment, there should be a small amount visible in the bottom of the silencer. Maybe.

RC had it right about the clear "silencer" that's inline. It not a filter at all but rather just a clear cylinder. He wrote:

"This 77 was originally fitted with the OE black offset device Porsche calls a "silencer" or really a small surface area filter. It was omitted after 78 or so and all later models had no main pump pre filter. Porsche realised that running any filter before the pump is not really a good idea. It can restrict flow, cause cavitation and in a worse case scenario melt pistons from leaning out, particularly on boosted applications.

http://aeromotiveinc.com/2010/01/fuel-filtration/

Obviously using rusted/ dirty/ old gas in 30yo tanks is not a Porsche design but typical of the neglected maintainance from many PO`s or indeed O`s.

Although there may be some fuel level variation visible in the inlet line at start up there should not be once the engine and pump have been running a very short while. Bubbles indicate very low fuel, cavitation or air leakage from hoses (especially prone with oversize hose), fittings, accumulator."

That's correct; the silencer filled right away and stayed consistent the whole time we were watching it. So flow is okay, for now.

Pulling the hose off and blowing air into the tank worked in this case, just to get it running but now we have to pull the sender and see what the hell is so large that it's able to completely plug that filter and prevent any gravity flow at all.

Probably have to pull the tank and have it cleaned and lined again. I didn't think that would be a repeat procedure but I guess so. It's a good time to replace all those hoses up there to prevent any fumes from entering the cabin.

I was just glad to get it running again. At least I now have a nice shiny new fuel pump, too. Sparkles!

One other thing. When we were taking off the rusty clamps, before we had any fuel present, I was using a screw driver to loosen a clamp and the blade slipped off and actually caused a spark. It could've been a disaster if there had been any fuel or fumes present, enough to ignite. Switched to a nut driver instead.

There Bnoon....you can have your stinky thread back now!
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'80 924 n/a SOLD

[bnoon]

No no no, it's not that easy. I'm going to come in here and threadjack you now! LOL!

'Grats on getting it figured. That's usually the toughest part. When you do pull the in-tank pump, give a light tug on the short hose that makes the connection from the pump to the threaded insert to make sure that connection is good and that the hose is still solid. Mine was a little loose and I thought it was good enough, but that caused the pump to fail due to constantly free-wheeling fuel past/around itself. That and the amazing amount of gunk I had in the bottom of the tank the first time I drained it. Good luck to you!
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'80 924 Turbo - SOLD!
1986 Porsche 944 Turbo - SOLD!
Porscheless

[D Hook]

I pulled the sender out today to see if I could see anything that would be down there blocking the outlet in the bottom of the tank and couldn't see anything. I fished around with a long, metal claw grabber and nothing came up. I pushed it down into the resevoir where the in-tank pumps sits and nothing came back. So I'm not sure what was blocking the flow and probably won't without pulling the in-tank pump out.

I took it for a long drive and it behaved as usual. No problems. Checked the platice see-though silencer while it was idling and it showed full and no variation in level so fuel flow seems to be back to normal.

Probably run out the rest of the fuel and then pull the in-tank pump out and see what comes out I guess.
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'80 924 n/a SOLD