No power to the fuel pump

XJTONY59

MEMBER
1999 JEEP CHEROKEE
4.0L
6 CYL
4WD
AUTOMATIC
178,000 MILES

While installing a switch for fog lights I left the key in the on position which caused a tiny arc at the switch and blew the in line fuse. Now I have no power to the fuel pump and my gauges do not move when I turn the key to on. But, all other systems are working properly; cluster lights up, heater fan works, radio, interior lights, exterior lights all work. I wired the fog lights independently they are not jumped off any other system. I replaced the crank position sensor, checked all fuses, replaced the fuel pump relay. Nothing has changed. No gauge function and no power to fuel pump. I am baffled. Please help!

7 Replies

CARADIODOC

MECHANIC
33,871 POSTS

How are you checking the fuel pump operation? Do you hear it hum for one second when you turn on the ignition switch?

Do any of the warning lights work on the instrument cluster?

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Thursday, August 3rd, 2017 AT 6:44 PM

XJTONY59

MEMBER
4 POSTS

I poked a tester into each of the four wires located on top of the fuel pump and got no response light, plus there is no sound at all when the pump is engaged. Yes the cluster lights all work including the seat belt warning light. The low fuel light activates for a second as well as the check engine light. The oil pressure needle moves slightly but the other needles do not move at all. Again, every other electrical system in the Jeep works. Crank no start. Also, I tested each fuse with the tester and a visual check as a back up. It must be something simple that I am missing.

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Thursday, August 3rd, 2017 AT 7:06 PM

CARADIODOC

MECHANIC
33,871 POSTS

I suspect you are expecting to have twelve volts to the fuel pump when you should not have it. That will only be there for one second when you turn on the ignition switch, then again when the engine is rotating, meaning cranking or running. If there was twelve volts there all the time, that would pose a serious fire hazard if a fuel line got ruptured in a crash.

For a crank/no-start, you have to check for spark too. About 95 percent of these no-starts are caused by a loss of injector pulses, fuel pump, and spark. All of these systems get their twelve volts through the automatic shutdown, (ASD) relay, and that is turned on by the engine computer. If you have a scanner, you can view the state that relay has been commanded to by the computer. If you do not have a scanner, the fastest way to know if the ASD relay is turning on is to back-probe the dark green/orange wire at the ignition coil pack, any injector, or either smaller terminal on the back of the alternator. A test light works best for this because most digital meters do not respond fast enough. If you see that twelve volts show up for one second when you turn on the ignition switch, the relay is working and the computer has control over it. What is important is if it comes back during cranking. If it does, you have an ignition system problem or a fuel problem, but not both. More commonly, if the twelve volts does not come back during cranking, it is because the engine computer is not seeing a signal from the crankshaft position sensor or the camshaft position sensor.

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Thursday, August 3rd, 2017 AT 7:27 PM

XJTONY59

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4 POSTS

Okay I am pretty sure I understand what you are saying and I will check that out tomorrow as it is dark here now. Hopefully I can resolve the issue with what you have given me. I will add another post after I have done these tests and I am hoping you are the one who is receiving that. Either way, I cannot thank you enough for your help. I am a disabled veteran with little money and this website is a Godsend. So thank you again.

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Thursday, August 3rd, 2017 AT 7:43 PM

CARADIODOC

MECHANIC
33,871 POSTS

Yup; this has become a private conversation between us. I am here most nights but sometimes I skip a night, so do not panic if I do not get back to you right away.