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Crank but no start found fried wire at junction box for fuel pump connection

Tiny
COREY WRIGHT
  • MEMBER
  • 1993 GMC C1500
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 125,000 MILES
First off, what would cause the wire to burn up? Second, I'm guessing the cause might be my problem?Truck ran fine, shut it off for 5 minutes, came back outside started and parked it in the lot, came out next morning and crank but no start. Started looking under the hood, and pulled cover off junction box and happened to see fried wire casing, the wire has a fusible link in it, and it's the wire leading to fuel pump label on junc. Box. I don't hear fuel pump engaging now, but assume it's not getting power.
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Sunday, December 15th, 2019 AT 8:38 AM

13 Replies

Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I'm Danny.

Can you take a picture of the fried wire you are speaking of with your phone and upload it here? I've attached a wiring diagram below. Let me know if it's the same fusible link. Hope this helps and thanks for using 2CarPros.
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Sunday, December 15th, 2019 AT 4:20 PM
Tiny
COREY WRIGHT
  • MEMBER
  • 9 POSTS
This isn't my truck as I'm not near the truck currently, but this is the wire that blew, the one that connects here. I hope this helps.
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Sunday, December 15th, 2019 AT 4:31 PM
Tiny
COREY WRIGHT
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  • 9 POSTS
My truck has the exact setup that this one does.
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Sunday, December 15th, 2019 AT 4:32 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Okay, I've added another diagram picture below. Does this look to be the junction box with the fusible link? Let me know or I will send more diagrams. On this diagram it looks like the Blue fusible link turns to red/black wire on the firewall junction box picture you provided. I've circled it in red. Hope this helps and thanks again for using 2CarPros.

Danny-
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Monday, December 16th, 2019 AT 3:07 AM
Tiny
COREY WRIGHT
  • MEMBER
  • 9 POSTS
That doesn't answer my question. I'm not an electrician man. I don't know what any of that means. I'm wondering what would cause the wire to fry, not where the wire goes to?
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Monday, December 16th, 2019 AT 5:17 AM
Tiny
COREY WRIGHT
  • MEMBER
  • 9 POSTS
So to update: I ran a tester to where the fuel pump relay hooks up and on the picture attached I can label what I found, but basically when I turned the key I didn't come up with a hot circuit on anything other than the constant power. If I understand correctly, when I turn the key forward I should get a positive reading on another pin for 3-9 seconds, but I did not. Does that mean it's the ignition switch not sending the signal to prime the pump?
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Monday, December 16th, 2019 AT 10:45 AM
Tiny
COREY WRIGHT
  • MEMBER
  • 9 POSTS
The wire that fried was the one furthest to the left in the photo. This is a pic of the fusible link, or what I'm calling a fusible link, let me know if that's incorrect.
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Monday, December 16th, 2019 AT 10:54 AM
Tiny
DANNY L
  • MECHANIC
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Hello again.

Sorry but I need to ask you another question. I've circled the picture you provided with two blue circles. Are we talking about the far left wire or the harness/plug with the green and red arrows? Get back to me when you can and we'll go from there. Thanks again for using 2CarPros.

Danny-
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Tuesday, December 17th, 2019 AT 5:21 AM
Tiny
COREY WRIGHT
  • MEMBER
  • 9 POSTS
The wire that blew was the wire all the way to the left. It's hot and has power, I have repaired the wire now, and the plug on the right I tested with a test light and it has one constant power, always hot. The red arrow, and two prongs with the green arrows tested as negative circuits I think ( the test light was green when I hooked the clip to a positive source and then touched all the prongs). That's where the relay for the fuel pump plugs in. Does that help with what you're asking? I'm not good with electrical stuff and I'm hoping to repair on my own because I don't have the money right now to have a shop fix it.
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Tuesday, December 17th, 2019 AT 11:22 AM
Tiny
DANNY L
  • MECHANIC
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Hello again,

I've attached 2 pictures below with a fuel pump wiring diagram. One is for your truck having an ECM (engine control module) and the second is for a PCM (power-train control module) If you can provide me with your VIN (vehicle identification number) I can check and see which module your truck has. Thanks again for using 2CarPros.

Danny-
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Wednesday, December 18th, 2019 AT 4:00 PM
Tiny
COREY WRIGHT
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Thanks I appreciate your answers, and I have the VIN here for you :
2GTEC19KOP1529812
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Wednesday, December 18th, 2019 AT 4:04 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again,

I tried calling my local Chevrolet dealer but couldn't find out anything due to not being in the system from being old.I'm pretty sure your has the PCM due to the dlc (data link connector) being in the diagram. I've attach other fuel system diagrams below and cut them into pieces to make larger in size. Tomorrow morning I will look at my truck to see if mine is the same. Mine is a 1989 K1500. Hope this helps and thanks again for using 2CarPros.

Danny-
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Wednesday, December 18th, 2019 AT 5:09 PM

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