Gary C2 UK

Hi all,

my 1990 C2 has developed a fault with the fuel gauge etc.

Here is a brief description of the symptoms and what I've tried so far.

1. The needle is saying empty as well as the low level light being on

2. I filled the car but no change. The car had been unused for a few weeks and I couldn't remember how much fuel was in the tank!

3. The needle still stays at the bottom but the light now flashes ever 10 seconds or so.

4. I grounded the green wire that goes from plug on the sender to the gauge and the needle moves to full but the light stays on(I think they work independently).

5. I reconnected the plug onto the sender unit and switched the ignition on and the needle now goes to full. At this point I thought it was just a sticking needle and it was now fixed! No such luck.
I start the car and after about ten seconds the needle drops back down to empty!!

6. I'm now back to the beginning and the needle will no longer move anymore.

My thought are this. Is the signal to the gauge to low to deflect the needle, in-otherwards is something dragging it low or is the sender itself faulty?

Does anyone know how to test the sender unit? Do you know of any resistance values between any of the four pins?

Could the central warning systom be playing up?
There are no other electrical faults with the car.

I've been told that later cars and ones that have had replacement senders have some extra "interface" between the sender and the original wiring. My car does not have any of this, it appears to be as it left the factory in '89.

Many Thanks ,

Gary

J richard

Gary,
I had this problem on an 84. It developed when the local municipalities required the use of oxygenated fuels. The additives in the fuel cleaned up all the varnish in the tank and goo'ed up the sending unit. (showing empty with the light on). The fix was to remove the sending unit from the tank, pretty easy just a spanner ring and the whole thing comes out. (you may want to run the tank down a bit so you don't spill any fuel) Some carb cleaner and paper towel and all was well with the world again. It sound like a very similar problem.

Hope this helps

Regards

Adrian

Dear Gary,
Quite a common problem on the 964 plastic fuel tank. Okay first thing to do is open the trunk/hood/bonnet, remove the carpet. Now looking from the front near the top on the LH side you will see a connector. This is the fuel sender. Remove this connector and give it a dry and maybe a bit of contact cleaner. Inspect the top of the sender for water. Give it a good clean up and dry it throughly. Reinstall the connector and give it a bit of a wiggle, do not be rough with it.
This normally fixes the problem. Now if it doesn´t the problem is most likely the fuel sender itself. Maybe a techincal thump on the side of the fuel tank may help. I would also check your fuel for water. Too much water in the fuel can also cause this same problem. The sender is not too difficult to remove. Often just a removal and clean up is good enough.
Ciao,
Adrian
911C4

PS: Do not ground sender wires in Porsches or any other autos for that matter. You can trash your instruments in short order doing this by driving the pointer movements against their stops.

Gary C2 UK

Adrian thanks,

I assume the sender is the big white plastic nut?
I've already tried the cleaning of connectors etc, this area was all perfectly dry.

I have also tried the "technical thump" with a rubber mallet. This was all attempted yesterday.

It looks like I'll have to remove the sender at the weekend to see if it is sticking. What I don't understand is how the needle on the gauge went up to full and the light went out then backdown to empty with the light back on.

How full a tank can you get away with when removing the senders?

Thanks,

Gary

Gary C2 UK

J richard,

thank you as well. It looks like it's going the fuel sender out way.

Gary

Adrian

Dear Gary,
Do not remove the sender with a full tank. About half full is the maximum. It is more than just spilling fuel as well. Do not forget to disconnect the battery or even remove the battery before you open the tank. Purely a safety issue.
I would when you have the tank open check for water. Obviously any water will be at the bottom of the tank.
Ciao,
Adrian
911C4