Fuel Gauage on full all the time 89 comanche sport truck

[ronald69]

Fuel gauage shows way pass full when i bought this truck. The shop says that there is some kind of resistor that has worn out completely through if so can this be fixed with a new sending unit or do i have live with this? Other then that the old truck seems to be decent. Help any suggestion ?

[maddzz1]

Not sure about the resistor but knowone has the sending units anymore. They will give you one for an XJ and then it won't fit.

[Eagle]

I suspect an open circuit.

 

There's a plug in the wiring harness about 15" outside of the fuel tank. Three wires. The heavy wire is power to the pump, the black wire is ground for the pump and sender, and the third wire (purple?) is power to the sender.

 

Unplug the connector. Turn on the ignition and the gauge should move all the way to one extreme. Not sure, but I think that's FULL. Then if you use a paper clip to jumper the connector from the sender power to the ground on the body side of the connector, the gauge should go to the opposite extreme -- which I believe should be EMPTY. Te sender is a variable resistor, with a range of 0 to 88 ohms. I think 0 ohms is EMPTY (which would be jumpered), and I think 88 ohms is FULL (and an open circuit would be infinite resistance, which is more than 88 ohms).

 

If yours does this, there is probably an open somewhere in your wiring. The wires inside the tank are push-on connectors, so if the previous owner ever had the pump out of the tank, he may have fubarred the push-on connector.

 

If your gauge doesn't react as above when you disconnect and then jumper the body side of the connector, then you have a wiring problem between the dash and the connector.

[ronald69]

The shop said everything checked out as you suggeted so the problem must be in the tank with those. The maechanic even tried some after market ones but isn't having any luck.