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James
James, Ford Technician
Category: Ford
Satisfied Customers: 3613
Experience:  Ford Senior Master Tech, Ford gas and diesel expert, ASE Certified
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WITH A 1999 FORD F250 7.3 DIESEL. TROUBLE CODES P1391 AND

Customer Question

HI IM DEALING WITH A 1999 FORD F250 7.3 DIESEL. IM GETTING TROUBLE CODES P1391 AND P1393. I HAVE ALREADY CHANGED THE GLOW PLUG RELAY AND SAME THING. WHAT ELSE CAN I DO TO DIAGNOSE WHATS WRONG/
Submitted: 1 year ago.
Category: Ford
Expert:  James replied 1 year ago.

Hello, do you have a bolt meter by chance?

Customer: replied 1 year ago.
VOLT METER? YES
Expert:  James replied 1 year ago.

If you test the voltage drop on the two large relay posts what do you get for a reading? It should be less than .3v if it's working correctly. This will make sure the PCM is turning on the glow plug relay as well. Then to test each glow plug through the harness. They should be between .9-1.9 ohms

Customer: replied 1 year ago.
HOW DO YOU TEST FOR VOLTAGE DROP? I PUT THE VOLT METER TO THE 2 POST WITH THE IGNITION ON AND I GET 12.47 VOLTS WHEN I TURN THE IGNITION OFF I GET 0.054 VOLTS.
Expert:  James replied 1 year ago.

To perform a voltage drop one lead will be on the battery post to the glow plug relay. The second lead will go on the other large post. When the key is off you will read 12v or battery voltage. When you turn the key on it will drop to zero if it's good. It sounds like you did it correctly. If that is the case your glow plugs will be causing your issue.