Fuel Pump Fuse Blows

Rickyll7 · Sep 25, 2008

BobHyatt said:
Here's the main thing. 99 out of 100 such problems are a bad pump motor, not a short. You can not tell whether the wire from the fuse is shorted to the body, or whether the continuity you are reading is through the pump motor. So to find a short, you are going to have to remove the tank anyway to disconnect the pump. Once you do that, you can now telll with 100% accuracy whether the power circuit is shorted or not. Or you can ignore than and simply connect the pump to your battery, being sure to use a 20a fuse for protection in case the motor is frozen/shorted internally.

But the tank is going to have to come down to diagnose this. I can guarantee you that any normal mustang will show continuity from the fuse to ground, because the motor is providing the continuity. It has to be removed to see if there is a short...

Let's not turn this into another "the clutch cable needs to be shortened as the clutch wears" type discussion...

Read posts 8 and 18. I believe it's either a short in the fuel pump wiring between the relay and the inertia switch, or possibly a PCM problem in light of post 18.

Rickyll7 · Sep 25, 2008

nyuk98gt said:
RickyII7:

The Owners Manual diagram is WRONG for 1998. The FP fuse is the one nearest the fender, the PCM fuse is the one nearest the engine. Both are yellow 20A fuses.

GL,

Chris

What is the PCM? Is that the same as the ECU? It's behind the passenger side kick panel right?

Also, its the # 25 fuse, its a 20 amp Maxi fuse.

nyuk98gt · Sep 26, 2008

RickyII7:

PCM = powertrain control module, or, yes, ECM (computer).

I'm on the road so I can't tell you what the FP fuse number is on my car. (Sorry).

Chris

Roblu98 · Sep 26, 2008

BobHyatt said:
Here's the main thing. 99 out of 100 such problems are a bad pump motor, not a short. You can not tell whether the wire from the fuse is shorted to the body, or whether the continuity you are reading is through the pump motor. So to find a short, you are going to have to remove the tank anyway to disconnect the pump. Once you do that, you can now telll with 100% accuracy whether the power circuit is shorted or not. Or you can ignore than and simply connect the pump to your battery, being sure to use a 20a fuse for protection in case the motor is frozen/shorted internally.

But the tank is going to have to come down to diagnose this. I can guarantee you that any normal mustang will show continuity from the fuse to ground, because the motor is providing the continuity. It has to be removed to see if there is a short...

Let's not turn this into another "the clutch cable needs to be shortened as the clutch wears" type discussion...

+1 (From a Electrician!)

JimC · Sep 27, 2008

PM me I might have a wiring diagram

Turbo92PGT · Sep 28, 2008

I had the EXACT same problem on my mustang. Except mine was intermittant. Then one day I punched it around a corner and the car shut off. I pulled over and tried putting in new fuses and they all blew. Towed the car home. Pulled the CCRM out and replaced that for good measure (junkyard one). No luck. Unplugged the fuel pump etc like you did. Kept blowing.

My problem ended up being the engine wiring harness at the back of the motor. It was hardly noticeable but what happened was the wiring touched against the EGR tube and shorted out a couple wires. Cut and soldered and insulated the wires and it was good as new. I have not had a problem with it at all since.

I have had my motor out of the car and I think I just neglected exactly how I ran the wires.

That would be my guess. Good luck, feel free to email me if you have any more questions.

Turbo92PGT@hotmail.com

Rickyll7 · Oct 5, 2008

any one have a fuse diagram for a 98 gt? or have any other suggestions?

Rickyll7 · Oct 5, 2008

Problem Solved!

It turns out that the fuse was the computer fuse as previously suggested. The 1998 gt manual is wrong. The MIL eliminators were the culprit. One of the wires was worn and shorting out to the transmission mount. I did some Google searching and found someone with a similar issue. His problem was a shorted MIL eliminator so I though I would check mine out.

Thanks to all who helped!

COramprat · Oct 6, 2008

Exactly what happened to me.

Inbreakable · Oct 6, 2008

your fuel pump wire runs almost in the middle of your trunk too. You may want to check that if you have screwed anything down in your trunk like amps or anything. It is right next to your dip that holds a spare tire. I had that problem once when I was relocationing my battery to the trunk.

FoxRod87 · Oct 9, 2008

I had the same problem and it turned out to be an oxygen sensor wiring rubbed and shorted against each other blowing the fuel pump fuse which powers everything. Glad you got it fixed.

Inked12679 · Jun 16, 2017

I have a 97 gt and I'm having the fuse issue. Just got headers h pipe installed and now the car is running hotter. Could this be the cause of my problem?

nyuk98gt · Jun 19, 2017

Inked12679,

An oldie but goodie thread!

All was good before the installation of the headers and mid-pipe, correct? If so, then something has happened so now we have to sort out what the issue is. I will say that the hotter engine bay may not be a likely cause because lots of people run headers (coated and not coated) and electrical issues do not result.

This is not much as much fun as modding but get the car up on jack stands and carefully check the wiring of the O2 sensors and the wiring harness that runs above the transmission (near the back of the engine). You'll need a mechanics mirror and a decent light. Even then, you will have to feel for melted insulation. If there is missing insulation then there will be a short when the bare wire contacts the body or something else that's grounded. Another possibility is that a wire got a little pulled out of a connector during the recent work, leaving a little exposed metal that can cause a short.

I don't have my Hayne's manual anymore but there are wiring diagrams in the back. Find the harness and see what else is bundled with the fuel pump wires. This will help you to figure out where to start (and where to go) if you don't want to start under the car.

HTH,

Chris

wmburns · Jun 20, 2017

+1 on above.

To anyone else reading this thread. There is an ERROR in the owner's manual for some model years between 1996 and 1998. The PCM fuse and fuel pump fuse are labeled backwards. Which means that you may think the fuel pump fuse is blowing when in fact it's the PCM fuse that is blowing.

Another oddity of the 1996-1998 model year Mustangs is the O2 heater circuits draw power through the PCM. Which means a ground fault in any of the O2 heater circuits will blow the PCM fuse. This is a terrible design that Ford changed in the 1999+ model years.

Suggestion. Verify which fuse is blowing. IF the fuel pump fuse is blowing THEN there should be no key on power at the trunk mounted IFS shut off switch. In the same vein the PCM should communicate with an ODB2 reader/scanner.

Be open to the possibility that if after the fuse blows and you are unable to communicate with the PCM, stop and think that maybe it's the PCM fuse that has really blown.

Fuel Pump Fuse Blows

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