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James, Ford Technician
Category: Ford
Satisfied Customers: 3630
Experience:  Ford Senior Master Tech, Ford gas and diesel expert, ASE Certified
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Glow plug problem.
, 2002 7.3, wasn't starting unless

Customer Question

Customer: ***** *****, glow plug problem.
JA: Thanks. Can you give me any more details about your issue?
Customer: 2002 7.3, wasn't starting unless plugged in, found bad gp relay, changed it, still not energizing the gp side, got power from batt to big post, and power on both little terminals, when i turn the key on the wire from cpm is not cutting the circuit to energize the relay, I took cpm wire of and grounded it and that energized the relay, same for the aih
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Submitted: 1 year ago.
Category: Ford
Expert:  James replied 1 year ago.

Hello, so when you ground the small post on the glow plug relay it energizes and the vehicle will start?

Customer: replied 1 year ago.
didn't get that far, batteries died, it will start after plugged in.
Customer: replied 1 year ago.
pcm has power, truck runs fine, even disconnected the eot to see if that would energize the relay, it didn't. its 30 and snowing here.
Customer: replied 1 year ago.
by energize, i mean create a ground.
Customer: replied 1 year ago.
would low batteries tell the pcm not to energize the gpr?
Customer: replied 1 year ago.
after charging the batteries, I created a ground and it started and looped and died, i did change the right side glow plugs, so have are new.
Expert:  James replied 1 year ago.

Each glow plug tested with an ohm meter to ground should be between .5-1.9ohms. If grounding the glow plug relay energized it and it started this is a bad ground inside the PCM itself. The repair for that will be to replace the PCM or run a manual switch to control the glow plug relay. If you energized it you should keep it energized for at least 45sec before attempting to start.

Customer: replied 1 year ago.
to fix it, i would have to change the pcm?
Expert:  James replied 1 year ago.

Correct if the ground driver in the PCM is bad. Replacing the PCM is the correct repair. If you wanted an inexpensive repair you could wire the small post to a switch inside the vehicle. Run the switch to ground you can manually control the glow plugs.

Expert:  James replied 1 year ago.

Hello, can I still offer you assistance? If not please remember to rate my answer so I receive credit for assisting you.

Customer: replied 1 year ago.
Your good, was hoping there was another answer, I wired a manual switch through a relay.
Expert:  James replied 1 year ago.

Wiring a switch is the route I have gone for many customers when this happens.