Fuel Gauge related problem

[5TTTj]

I think I searched and read everything related to my problem but here's my situation.

Ive had an inoperative gas gauge for several months, I was planning on changing out the sender and fuel pump assembly soon, but this week I've been doing a few things to the jeep and had disconnected the battery while completing my work, twice now I reconnect the battery I've noticed the gas gauge working fine for a few minuets before dropping to empty again.
So far I've looked at the Plug / Wiring at the top of the tank ( driver side ) and have done the gauge cluster test with the trip OD pressed and the Key on. everything looks good.
Any ideas ??

 

[macleanflood]

Continuity check from the fuel tank plug all the way back to the PCM pin.

-Mac

 

[Obi-Wan]

Continuity check from the fuel tank plug all the way back to the PCM pin.

-Mac

@5TTTj, Specifically PCM pin C26 of the GRAY connector on the PCM. DB/LG = Dark Blue wire with Light Green tracer.

You should also check continuity of the sensor ground on pin A4 of the BLACK connector on the PCM back to the sensor ground on the sender plug to ensure the entire wiring loop is cromulent. BR/YL = Brown wire with Yellow tracer.

Below is the wiring diagram highlighting the fuel sender wiring loop.

 

[5TTTj]

Oh man - Thank you both.
Wiring is probably my weakest area as a DYI mechanic, last evening I did look at the FSM sticky and was able to find connector C26 which Mac said to use for my continuity test to the tank plug, Looking at the wiring diagram it look like the wires a dark blue with a white tracer and light green with a black. Is that the same color wires I'll find at the at the tank plug also ? Again thank you both for making this easier.

 

[Obi-Wan]

Oh man - Thank you both.
Wiring is probably my weakest area as a DYI mechanic, last evening I did look at the FSM sticky and was able to find connector C26 which Mac said to use for my continuity test to the tank plug, Looking at the wiring diagram it look like the wires a dark blue with a white tracer and light green with a black. Is that the same color wires I'll find at the at the tank plug also ? Again thank you both for making this easier.

View attachment 554236

Wiring color from C26 to the tank plug will match same as from the tank sensor ground back to A4.

Also, It looks like you're looking in a newer model year manual. Your profile states you have a 97, correct? Not all TJ's carry the same circuit numbering for the wiring diagrams throughout the years, so be careful and select the correct year manual for your Jeep.

 

[5TTTj]

yes 97

 

[5TTTj]

Dang it, you're absolutely correct. I have a Ford truck that is a 99 and for some reason I often get them switched.

 

[Obi-Wan]

Dang it, you're absolutely correct. I have a Ford truck that is a 99 and for some reason I often get them switched.

All good. Just making sure you don't unintentionally confuse and frustrate yourself.

 

[Jezza]

Don't forget to check for shorts to the chassis on that sending unit wire as well. We had an 05 Rubicon in last week with an intermittent fuel gauge. The tech found wires with missing insulation near the bell housing. The sending unit wire was shorting to the engine block and reading incorrectly.

 

[freedom_in_4low]

maybe it was different in 97, but when my 2006 fuel level signal went away, I got a CEL and a code. There's different codes for whether the signal voltage is too high or too low, which will tell you whether it's open or shorted.

Mine was indeed the level sender, but I could tell that because the gauge always went dead at the same fuel level (about 5/8 of a tank) and it would come back if I just turned the engine off and back on. If it's random regardless of fuel level then it's more likely in the wiring between the sender and the PCM.

 

[lBasket]

Don't forget to check for shorts to the chassis on that sending unit wire as well. We had an 05 Rubicon in last week with an intermittent fuel gauge. The tech found wires with missing insulation near the bell housing. The sending unit wire was shorting to the engine block and reading incorrectly.

Is there a way to check for shorts other than visually inspecting the wires? Always wondered this

 

[Jezza]

maybe it was different in 97, but when my 2006 fuel level signal went away, I got a CEL and a code. There's different codes for whether the signal voltage is too high or too low, which will tell you whether it's open or shorted.

Mine was indeed the level sender, but I could tell that because the gauge always went dead at the same fuel level (about 5/8 of a tank) and it would come back if I just turned the engine off and back on. If it's random regardless of fuel level then it's more likely in the wiring between the sender and the PCM.

The one here did have an intermittent code for the fuel level sensor. The light wasn't on when it came in however.

 

[Jezza]

Is there a way to check for shorts other than visually inspecting the wires? Always wondered this

Measure resistance to ground on that wire. It should not be 0.

 

[freedom_in_4low]

The one here did have an intermittent code for the fuel level sensor. The light wasn't on when it came in however.

Yeah, it'll clear the light if it doesn't happen for a couple of drives. The signal has to be open or shorted for 90 seconds to trigger the code.