91 Wrangler fuel guage issues

[Purple Frog]

My grandson just had to have a Jeep.

His parent bought him a 91 with the 4 banger. So I have spent a LOT of time doing repairs.

The fuel guage quit working. Cut the tailpipe, dropped the tank, and installed a new fuel pump/sender unit assembly.

Now, turn on ignition the guage reads fine. Start driving, guage reads fine. Hit it brake pedal, guage drops to zero.

Only one other issue with vehicle currently. I'm only mentioning it because of any possible relationship.
The brake warning light on the steering column stays lit no matter what. All four corners have new brakes, new master cylinder (full), bled properly.

Anyone got any idea where to proceed?

I'm worried that the symptom could be causing the sending unit to burn up. So, i don't want to keep hitting the brake.

ECU starting to fail?

Thanks in advance.

 

[xt master]

As far as the brake light staying on orbit the same light for the E brake? Not sure on the YJ if it is maybe something wrong with the E brake switch. As far as the gas gauge maybe a bad wire or ground? I am not sure if They are eltronic or Manuel gauges in a 91

Jeep! not just a vehicle a way of life.

 

[Purple Frog]

I have pulled out most of harness and inspected.

Checked all the grounds.

Removed the left over wiring from many previous owners attempts to install stereos of different vintages multiple times.

I have dash apart.

I think i may have a turn signal switch issue, so I have ordered a new Crown unit.
(Left brake light only works if turn signal is on, right is OK)

Suspect I need to change out the guage cluster unit (Chrsler #5600151767545).
Only available used, so i could be buying anothers problem...

 

[NickLuzier]

Pull up a wiring diagram on year of his jeep if you haven't done so already. Looks like coming off the PCM there's a wire that goes to the brake switch and a wire that comes off the brake switch that ties into the fuel pump relay and the automatic fuel pump shut down relay. Might be some type of wiring issue in that area. Just use the wiring diagram and chase the wires to look for corrosion or bad spots in the wiring. Just my 2 cents.

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[Purple Frog]

Now I have changed out the turn signal switch in the steering column.

All the same problems remain.

Fuel guage goes to zero when brake applied.

Rear brake lights sporadic.

 

[Bill b]

Grounds??

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[xt master]

It really sounds like you have a damaged wiring harness some where. It might be time to start tracing the wire for the brake switch from the pedal to the brake lights and same with the fuel gauge.

Jeep! not just a vehicle a way of life.

 

[Purple Frog]

The rest of the story...

With the fuel tank dropped, we pulled the pump/sending unit and moved the float through its range of motion while attached to the harness. Nothing happened on the guage. We plugged in the new pump/sending unit (~$200) and the guage worked fine. We thought we had solved the issue. Not.

Since we own a very expensive Snap-on scan tool we thought we would check the ECM. That required buying a ~$50 adapter. The scan tool said the ECM had a bad fuel guage reading. So, not being able to purchase a new ECM we shipped ours off to a rehab facility (~$200). Three days later it was back with a note saying they found nothing wrong.

Took the dash apart and cleaned all the contacts on the printed circuit.

Bought a new turn signal unit and installed it under the steering wheel. Brake lights and turn signals all seem to be working correctly.

Bought two manuals hoping to get a good wiring diagram. Not.

Pulled apart the harness and with an ohm meter checked out each wire. No issues.

But wait. During this endeavor we discovered the ground for the sending unit on the tank is attached to one of the sheet metal screws that attach the left rear taillight assembly to the body. Cheesy. Fixed that.

All systems go.

Noticed on test drives the beast will not exceed 55 mph. Thinking clogged catalytic converter. Exhaust system looked like swiss cheese, and we had to cut the tailpipe to drop the tank. So replaced everything from the manifold back. Including new catalytic converter. We could have done away with the cat, but didn't want the customer to be seeing codes on the dash.

Still, 55 is top speed.

Noticed that now the guages are working, it does not get hot, or even warm. P.O. had a 180 thermostat in the beast. Could it be that the ECM is seeing a cold engine and not letting it run correct? In process of changing it to a 195 discovered the radiator looked like a coral reef inside. So, new rad, new coolant, new thermostat.

Moral of story. Jeepz posters may have been spot on. Spent about $600 trying to fix a fuel guage when it might have been Chrysler's super cheap method of providing a ground for the fuel sending unit. Or... did the P.O. jury rig that ground during a previous tank exchange?

Now... to figure out why it will not exceed 55.

 

[JPNinPA]

Do you have bigger tires than stock? And is your speedometer correct?

Check fuel pressure even though you just changed it.

Clean air filter?

Does it accelerate through the pedal or does it stop at some point? If so TPS


JPNinPA
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