How to Test the Fuel Sending Units in a 1990 Jeep Wrangler
- 1). Raise the rear of the Jeep by placing the floor jack under the rear axle housing. Place the jack stands under the axle tubes and lower the vehicle so it rests on the stands. Turn the ignition switch to the “On” position without starting the vehicle.
- 2). Disconnect the fuel pump and sending unit harness just behind the fuel tank. Locate the power terminal in the engine side of the harness connector. Place the voltmeter black ground wire on a good ground. Probe the terminals for a terminal that has constant power using the red lead.
- 3). Install the alligator clip on the jumper wire to this terminal. Have a helper just watch the gauge while you momentarily touch the other alligator clip to ground. If the gauge moves toward the full mark the gauge is all right. If the gauge does not move the gauge is bad.
- 4). Turn the ignition key off. Turn the dial on the volt or ohmmeter to ohms. Leave the black lead on a good ground and check the remainder of the terminals in the harness connector with the red probe, to check for a good ground. When a good ground is located, the display will go from a zero to a point followed by the amount of ohms, if any. If no ground is indicated, follow the black wire in the vehicle harness to the ground on the frame.
- 5). Loosen the bolt with a wrench and clean any rust off the frame. Reinstall the ground. Retest to ensure the ground is good and has no resistance.
- 6). Replace the fuel sending unit if the gauge still fails to register even though it was found to be good and the sending unit has a good ground.
