fuel gauge

Jeff Alton · 09-15-2003, 08:49 PM

I need some help here. My fuel gauge is acting up. The needle will work it's way down from full as fuel gets used but doesn't go much below the half a tank mark. Then the low fuel light comes on and low and behold it is time to fill the tank. The light is accurate as I put 73 liters into my 80 liter tank today when I filled it up with the light on. Gauge of sending unit? Who knows how to test one or both of them?

thanks, Jeff

RoninLB · 09-15-2003, 10:59 PM

it's probably your sender..
I think the easiest way to go is to ground the sender lug in the back of the gauge.. if the gauge is OK then it'll peg.. but I haven't done this on a 911 yet.. so maybe get a confirm before trying it

fstar · 09-16-2003, 07:06 AM

Mine just started doing the exact same thing...anxious to hear what we should do.

RoninLB · 09-16-2003, 07:09 AM

Quote:

Originally posted by fstar
...anxious to hear what we should do.

I wouldn't pull the sender without another new rubber gasket handy. but the sender can sometimes be operated on.....Ron

LeRoux Strydom · 09-16-2003, 07:18 AM

It sounds like the sender. It is possible to clean the sender by removing the sending unit from the top of the fuel tank (six 8mm nuts if I recall correctly) after removing the connector plug. Carefully remove the cover sleeve from the unit on the bench by unscrewing the small nut at the bottom and sliding it off. Be careful as there are very thin long wires inside, against which the float slides to create the varying resistance. I cleaned these wires very carefully with fine emery cloth and some electrical contact cleaner. This restored full range function without the erratic jumping that I observed on the gauge prior to cleaning the sender.

The fact that the fuel low light comes on in your car suggests that the contact wiresinside the sender are dirty, as the idiot light is only triggered when the float slider gets to the bottom of the unit (i.e. when the tank is low). I would however test the gauge first by grounding the wires that run from the sender to the gauge to test full/empty indications on the gauge. I cannot remember which wires do what, but there are only three so it is not too difficult to play around. Just be careful with sparks around the fuel tank. usual disclaimer, etc.etc.

Good luck

LeRoux

RoninLB · 09-16-2003, 07:28 AM

Quote:

Originally posted by LeRoux Strydom
I would however test the gauge first by grounding the wires that run from the sender to the gauge to test full/empty indications on the gauge. I cannot remember which wires do what, but there are only three so it is not too difficult to play around. Just be careful with sparks around the fuel tank. usual disclaimer, etc.etc.

I would pull the gauge and ground the green wire lug to test the gauge

LeRoux Strydom · 09-16-2003, 07:34 AM

RoninLB

yeah, you're right, probably safer. It should be possible to test full range function from the gauge connectors. If you can find a manual it should tell you which wires to test for full/empty. I am not near to my Bentley manual so can't tell right now.

LeRoux

RoninLB · 09-16-2003, 07:57 AM

Quote:

Originally posted by LeRoux Strydom
RoninLB

If you can find a manual it should tell you which wires to test for full/empty.

yep.. the '77 Workshop man shows a green wire

Jeff Alton · 09-16-2003, 10:15 AM

Thanks for the help. I pulled the sending unit and cleaned the thin wires and reassembled it. Works perfectly now. Thanks again.

Jeff

Jeff Alton · 09-16-2003, 10:16 AM

Thanks for the help. I pulled the sending unit and cleaned the thin wires and reassembled it. Works perfectly now. Thanks again.

Jeff

Jeff Alton · 09-16-2003, 10:16 AM

Thanks for the help. I pulled the sending unit and cleaned the thin wires and reassembled it. Works perfectly now. Thanks again.

Jeff

Jeff Alton · 09-16-2003, 01:16 PM

I really only posted once, i think it was while the server was having some trouble!!! oh well.

Jeff