Joe '87 S4

I'm guessing it's a faulty connection in the gauge itself. My gas tank has been cleaned out and everything replaced/cleaned about 4 years ago. All ground points cleaned and the gauge cluster sent out to be refurbished and everything has worked as it should the past 4 years. That's why I find it odd that it just started happening about a week ago.

bronto

I noticed my temp guage doing this yesterday.

StratfordShark

Mine is the same. But it behaves wildly in a very consistent way! What I mean is the needle will flicker at certain regular points as the gauge goes down. I'm fairly ceratin this indicates a dirty fuel sender unit (under carpet, right side of rear hatch) screwed into top of tank. A float moves up and down a wire to change resistance from about 75 ohm to zero, and I understand this wire can get corroded/dirty so float loses contact at certain points. You can clean it with engine cleaning solutions.

So far I've checked that bridging the sensor connector gives correct 'low fuel' warning light behaviour.

I've bought a little 100 ohm preset pot so I can pull off the sensor connector and simulate the sensor resistance change, to confirm gauge is OK. My worry though is that the preset only handles about 0.2W so will it just melt when I connect it across sensor socket? I think I really need to find a big wirewound 100 ohm pot.

According to service manual you need a special porsche part pin wrench to undo the union nut clamping sensor into tank. People have also had problems freeing the sensor and with putting it back tight enough to avoid fuel fumes. I've bought one of those adjustable rubber wrenches (to open can tops!) and hope that will do the job so long as it will fit round the nut (not much space around it between nut and hole in hatch floor).

If anyone has advice on removing/refitting fuel sender, or just on this theory, then I'd be grateful!

Adrian

AJK

Just to add one more data point, my fuel gage would jump around when the level got to 1/4 full. I removed the sender unit from the tank and cleaned the two resistance wires that the float slides up and down on.

Problem solved.

blown 87

We do a LOT of fuel pumps here at the shop on other than Porsche's. Most cars have the same type of set up.
What we do is take a large set of water pump pliers and set them so the will just engage the lugs of the cap, then use a bar to turn it. We do not put any pressure on the cap with the pliers by squeezing.

They are not usually to bad to get off, sometime we have to take a couple of big flat punches and 2 of us tap on it 180 degress apart in the counterclockwise rotaion to get them off.

If you do this on a plastic tank, do it with not much fuel in it and put the cap back on while you are working on the sender or pump, belive it or not the plastic can somehow grow to the point that you can not get the cap back on if it is full of fuel when you take it off.

Greg N

StratfordShark

Thanks for excellent tip Greg!

Best,

Adrian

jpitman2

I lube the cap and the tank top threads (vaseline), and then tighten with a pair of large screwdrivers crossed over each other.
jp 83 Euro S AT 50k