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It is blowing PCM fuses as soon as I turn on the ignition.

Customer Question
it is blowing PCM fuses...
it is blowing PCM fuses as soon as I turn on the ignition
JA: Do all the fuses have the correct amperage for the circuits they're in?
Customer: yes
JA: What is the model/year of your Ford?
Customer: 1997 Ford F150
JA: Are you fixing your F150 yourself? What have you tried so far?
Customer: Looking for wiring shorts
JA: Anything else you want the mechanic to know before I connect you?
Customer: Nothing I can think of
Submitted: 1 year ago.Category: Ford
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Answered in 2 minutes by:
10/23/2016
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago
A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6,690
Experience: ASE Master Certified, ASE Advanced Gasoline Engine Performance
Verified

What are the fuse # locations and also are they under the hood or under the dash?

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Customer reply replied 1 year ago
Under the hood. It is the PCM Fuse #24
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Remove the PCM power relay in the same fuse box and see if the fuse still blows.

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Customer reply replied 1 year ago
The fuse blows as soon as I turn on the ignition. Shall I still remove the PCM relay?
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Yes, the fuse powers the PCM power relay. If you remove the relay, and the fuse blows or not, we'll know what direction to go.

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Customer reply replied 1 year ago
With the relay out, the fuse did not blow when I turned on the ignition and turned over the engine
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Ok. Do you have a digital multimeter?

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Customer reply replied 1 year ago
Next move?
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Ok. Look on the side of the relay and the bottom. The pins should be numbered, 30, 87, 87a, 85 and 86.

With the relay out of the fuse box. Check and see what pins in the fuse box for the relay have ground when the key is turned on. There should only be one.

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Customer reply replied 1 year ago
How do I check this
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Set the digital multimeter to volts and place the red lead of the meter on the positive post of the battery and the block lead you touch each pin in the relay socket of the fuse box one at a time. You will get battery voltage on the meter reading 12 volts if there is a ground on one of the pins. Do this with the key turned on.

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Customer reply replied 1 year ago
it will take a minute to find my digital multimeter. stand by
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

No problem. I'll be on line till 10:30 PM EST. I live on the East Coast.

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Customer reply replied 1 year ago
30,85,87 have ground; 11.8 volts
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Remove the fuel pump relay and see if you still have ground on pin #87.

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Customer reply replied 1 year ago
Fuel Pump Relay removed. Still have 11.8 on 87
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Does it change with the key turned off compared to being on?

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Customer reply replied 1 year ago
Next?
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Does it change with the key turned off compared to being on?

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Customer reply replied 1 year ago
I'll check
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Thank you.

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Customer reply replied 1 year ago
With ignition off, I still get 11.8
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

You have something grounding out that circuit. Have you had any work done to the vehicle recently and also, what engine does your F150 have?

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Customer reply replied 1 year ago
5.4 Liter. Recently added new radio, but took fuse out as part of testing before I contacted you. Added fog type lights.
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Check the wiring harness on the passenger side of the engine that goes down to the transmission. We have seen these harnesses contact the exhaust manifold and melt to the metal.

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Customer reply replied 1 year ago
Nothing making contact with exhaust manifold or showing bare wire
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

I am going to have to do a little digging through the wiring diagrams. Is it ok to continue this tomorrow evening?

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Customer reply replied 1 year ago
I'll be home after 5 pm eastern
Ford Mechanic: A. Penland, Ford Senior Master Technician, ASE replied 1 year ago

Sounds good. Good night.

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A. Penland
A. Penland
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Satisfied Customers: 6,690
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