rheacox

The gas gauge in my 98 Sport has read empty for the past month or so. Finally decided that it was time to investigate yesterday. Cycling through the overhead console to the DTE screen showed OC which I took to mean open circuit.

I tested the gauges by holding the trip reset and turning the key, they all worked fine. I tested the sender pins at the pump plug and got ~280 ohms at empty and ~40 ohms at full. I then jumped the pins for the sender on the plug and checked the pins at the PCM, nothing. If I understand everything right, it should have showed close to 0 ohms if the pins were jumped at the plug by the tank?

I read that the wires are spliced twice between the rear plug and the PCM. My guess is that one of those splices opened up but I have no clue where the harness runs. Any info would be greatly appreciated. Thanks

Xavier Matos

I have a 97 Cherokee Sport with the same problem. My gas gauge just went out one day. I checked all contacts and I also performed the diagnostic test and the gauge itself works, but it won't read the fuel level.

cruiser54

Check here for a downloadable manual.

http://cruiser54.com/?page_id=365

rheacox

I got mine fixed after some more investigation. I found where the harness goes through the floor under the rear seat and cut the insulation off the fuel sender wires and jumped them. The gauge then showed a full tank. I then checked both wires from there to the fuel pump plug and found that one of them had broken. Spliced the wire back together and covered everything in heat shrink. Problem solved.

cruiser54

Nice job.

Xavier Matos

I'm glad you got it fixed. I'm going to try this next. What do you mean you jumped the wires from the sending unit? How do you do that?? I'm also going to check for a broken wire like you did. Thank you.

rheacox

With the insulation stripped off of the wires under the seat, use a jumper wire to connect the two fuel sender wires (effectively telling the PCM that the tank is full). If the gauge works, the break is between the sender and that point. If the gauge does not work the break is between that point and the PCM. I only tapped the wires under the seat because it was the easiest point to get at the harness in the car. My wire was broken very close to the connector of the fuel pump. Hope this helps

Xavier Matos

Thank you for your response, you're very helpful. What is a jumper wire, and how can I get one or what do I need to make one? Also what color are the sending unit wires I should be looking for? Sorry for all the questions, I'm new to all of this stuff.

rheacox

There are 4 wires in the harness leading to the fuel pump assembly. 2 are for the fuel pump, and 2 are for the sender. I'm not positive but IIRC, the sender wires are blue with a green trace and brown with a kind of lime green trace. I should have taken pictures but I forgot. Maybe someone else knows for sure.

As for the jumper wire, anything will work. Hell, you could strip a wire bag tie and that would work. Once the insulation is stripped off the sender wires, you just need to connect them together with another wire. I suppose if you have to, you could just cut them and splice them right together.

Xavier Matos

Ahhh, ok. Thank you for clarifying this for me. I will look for these wires. Once I splice them and then turn the key the fuel gauge should read full if the broken wire is from there to the fuel pump assembly, but if it still reads empty the broken wire could be from there to the pcm? Thanks again.

rheacox

Exactly! If I had to guess though, it'll probably be where the wires are under the car exposed to the elements.

Just out of curiosity, did you check the resistance of the sender at the pump plug with a multi meter? There is always the chance that the sender itself has gone bad.

Xavier Matos

Ahhh, ok. I actually just replaced the whole fuel pump assembly since it had spliced wires on the harness by the plug, and I also thought my sending unit was bad since it looked black/burned on the resistor rail. It looked like the one that was originally in the jeep because it says ZJ on it, but now I'm thinking maybe that sending unit was still good and it could be a broken wire some where from the new harness to the pcm like you were saying. The only reason I didn't test the sending unit was because I don't have a multi meter at the moment.

Xavier Matos

Hey, back again with an update. I got my gas gauge working again thanks to you my friend @rheacox. It turns out I had a similar issue as yours. I checked the wires that connect to the fuel pump module assembly harness and lead into the cab, and right away I noticed a green wire with a white line on it had been melted so bad that it was melted with the other wires, and so I carefully separated the wires without damaging the copper inside and then wrapped it with electric tape, and then put the plastic wire cover back over the wires. I then went in the cab, and found where the wires enter, and I saw they were all taped together with electric tape, and after further examination towards where the wires go into the big black set of wires that lead to the pcm I noticed this same green wire with a white line was melted here as well, but nearly the whole wire from where it enters the cab to where it goes into the bigger set of wires along the floor, and it was melted so bad that it had melted the other wires to the point where all copper from each wires was exposed, and touching each other. Ironically the wires were only melted up to the point where they go into the big black wire harness that leads to the PCM so I dont think I need to go any further. What I did was carefully sliced the rubber from each wire, putting them aside separately, and once all stripped I wrapped each one individually with electric tape and bam, gas gauge turned back on with correct reading. So you think the wires would be fine with the electric tape or should I replace the wires, or is there something I can use to ensure they don't burn the electric tape?

rheacox

Nice work. However, having had my Jeep almost burn down earlier this year because of a short near the tail light, I would definitely suggest replacing the wires.

Xavier Matos

Thank you, I couldn't have done it without you. Omg �� so what do you think is best, buy wires and cut the old ones where they're exposed and then splice them or follow the wires to the PCM and replace the entire wires?? The latter seems like it would be hard since I might have to remove the floor side panels and maybe more to get to the wires. I checked the wires by the fuse box under the hood since I remember the colors and they looked fine. Thanks for the advice.