Here's 1 answer (well, enlargement anyway), and 2 queries.
My level gauge wasn't working - well, if watched carefully at switch on, it flicked up away from the bottom, but nowhere near full, which is what it was. Out with the sender unit. This is a 1 1/2" dia alloy tube, ~14" long. Plastic cup thingy on the bottom, held on with small nut (~2mm thread). Is that rust I see before me?
No, just congealed old gasoline stuff - chipped it off, undid nut. The cup thingy has 1/4" of more congealed hard brittle crud in it - clean this out. Next there is another nut holding a plastic cap in the end of the tube. After chipping away more crud, get the nut off, and after a bit of a struggle the plastic cap comes off. It engages the end of the fuel return pipe also. There is a rod going the full length of the tubing. It has a fitting on the end with 3 fine wires going to the far end, matching the three electrical connectors on the top. The float assy should slide on this central rod, changing the signal to the gauge head as it moves on the wires - not mine! The central rod had some of the congealed stuff on the bottom couple of inches, as did the fuel return tube. I couldn't remove the outer alloy tube from the top plate - seemed to be pressed into it somehow, so I had to carefully dislodge as much crud as I could with a thin long screwdriver, shaking it out as I went, a bit of WD40 now and again, and eventually the float would move with only the help of gravity. Reassembled, and we have a gas gauge again. I guess if any of the fine wires are disconnected, the unit is toast, but otherwise a good clean would seem to fix it. It would have been nice to wash it in something that would dissolve the crud, but I didn't have anything handy. I think I will replace the fuel
filter pretty soon too.
From all the talk of tank screens , do I wait until there isn't much in the tank, and get one hand through the hole and go fishing for this screen? How is it fixed inside the tank - it obviously can be removed through the top hole? Metal or plastic? Folds/scrunches up to come out? Cant visualize it yet.
Now - hot air all the time in the side vents - looking for the hot water valve - under the air box ? Got the 2 bolts at the ends inside the box, but where is the other fixing? I can see a small hex socket screw of some sort diagonally down the center cavity in the box, but cant see how to release the center of the box from the air measuring plate body?
Relays - are most/all standard types- any Bosch/Hella will do? -This is a CIS 83 Euro, so no specials for EFI stuff here.
From: Dan [mailto:email@example.com]
Sent: Sunday, March 04, 2001 7:11 AM
Subject:  Re: Fuel Sender removal
Looks like everyone is working on gas tanks this weekend. Mine is out but I spent most of the day cleaning it up for installation.
There is a special tool to remove the big ring. I use large channel locks and just twist. The unit itself is held in by a rubber gasket and can be pried out without much trouble. There is a cup on the end of the sending unit that can catch on the baffle but this is just a matter of shifting the unit back and forth. The baffle is spot welded to the bottom of the tank and can come loose. If this happens then ten to one the tank screen is busted too.
Shake the sending unit - the light connection can come undone and will rattle around inside. The unit is held together with a nut on the bottom. I can be taken apart and inspected and repaired. Check the filler tube for old gas or corrosion.
From: John Eifert [mailto:JohnEifert@hotmail.com]
Sent: Saturday, March 03, 2001 3:37 PM
Subject:  Re: Fuel Sender removal
How did you get the big black nut off? I have a spare sender that haven't installed yet. Looked at it today but decided to put it off till tomorrow and finish the interior 1/4 panel replacement after seeing that thing.
1983 928S US AT x 2
Hi, On my 87 S4 I'm trying to diagnose the level sensor. Currently trying to remove the sender unit out of the tank. I have removed the big black nut but it still will not come out. I have been able to lift it up about 1/2 inch but it seems to be contained by something else.
Any ideas? and solutions.
Finally got it out, the cup on the bottom of the sender unit was getting
caught on the baffle hole in the middle of the tank. A word of warning!, if
you are trying to diagnose a problem with the fuel gauge and reserve warning
light, my last resort would be to remove the sensor unit.
My sender turned out to be fine and now i need to tackle the gauge calibration.
Trying to get the nut back on the fuel tank was a real pain in the butt, the sender does not sit parallel to the flange so it kept causing the nut to cross thread. Took me well over an hour to have success.
I take my hat off to the Porsche assembly people here, and I know where i would stick it in the person who designed this setup. YMMV
A very good instruction document:
Fuel Sender replacement.pdf