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George H.
George H., ASE Certified Technician
Category: Jeep
Satisfied Customers: 18817
Experience:  ASE Master Tech 15+ years
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1992 jeep wrangler 4.0, auto. when the temperature falls

Customer Question

1992 jeep wrangler 4.0, auto.
when the temperature falls below about 50 degrees the fuel pump will not come on. park the jeep in the sun for a couple hours and the fuel pump comes on as it should briefly before cranking the engine over. I can make the fuel pump come on by warming the area around the under dash fuse box and steering column with a heat gun. Help.
Submitted: 2 years ago.
Category: Jeep
Expert:  George H. replied 2 years ago.

Hello I will help you with your question,

Can you try heating the computer located on the engine side of the firewall from the inside fuse block to see if that is the component being affected by the heating?

Not too hot just warm it up.

I am not sure what in the fuel pump circuit would be affected by heating under the dash fuse block as all the control for the pump is on the other side of the firewall.

Let me know what you find so we can work this out.

Thank you

Customer: replied 2 years ago.
I already tried warming the computer and the relay / fuse box under the hood before I tried warming under the dash.
That did not help. Seems that warming under the dash is the only area that will make the fuel pump come on.
Expert:  George H. replied 2 years ago.

I don't know what else might be under there, do you have any aftermarket alarm that might be spliced into the pump wiring?

Customer: replied 2 years ago.
No alarm, nothing aftermarket.
Expert:  George H. replied 2 years ago.

I don't know what would be affected by temperature then, all the fuel pump components are under the hood. The computer gets the signal the key is on and the engine is turning so it grounds the relay turning the pump on.

Sorry but without being there I don't think I can give you an answer so I will OPT OUT of your questions and maybe someone else will have a suggestion for you