Chrismorton10

Hey guys, I'm new to this forum and I need all the help I can get. I have a 02 GC with the standard 4.7. I'm having a problem where the injector fuse (#26 in PDC) blows under moderate to hard acceleration. In an effort to fix it I checked the wiring harness near the fuel rail and under the PDC for any frayed or exposed wires but I found nothing. It's got 182K on it and the previous owner never did injectors on it so I replaced those thinking maybe one was shorting out under load. Needless to say it did not fix the problem. I'm not really sure where to go after this but any suggestions would be much appreciated. Thanks!

BlueRidgeMark

Well, a blown fuse means a short. Somewhere. Ya just gots ta doo the tedious work of chasing wires.

Chrismorton10

I've gone through and checked all the harnesses and even where it goes behind the engine against the firewall, I see no shaved or otherwise damaged wires. Why is it that it only blows the fuse under moderate to heavy acceleration?

BlueRidgeMark

Engine mounts shot? Engine is torquing over and something is making contact?

Chrismorton10

Okay I can check around there. Do you have anywhere in mind I should try looking? Just around the motor mounts? It doesn't seem like then engine rocks a whole ton when its revved up but it does move. Do you know all the locations for the ground straps? or at least the most important ones? I know thats something good to look at as well. Thanks a lot!! I really appreciate the help!

BlueRidgeMark

A link to photos of all the ground locations can be found in my sig, #1. But bad grounds don't blow fuses.

Chrismorton10

Okay, so yesterday morning I started it up and it was running like crap, sputtering and finally stalled out, pulled two new codes. P0320 and p1391, along with p0300-0308 (not new). I know p1391 relates to loss of crank position sensor signal but it has a brand new sensor as of like a month ago. I did some reading on p0320 and it's something about engine ignition/distributor speed circuit. I cleared them and started it up again and drove it around, it seemed fine. It's definitely not running as good as it should, it feels sluggish and boggy but not sputtering out and dying like it was when I started it. Im going to watch and see if they come back but I've driven 3 times since it happened and I only have the misfire codes. They were all cold starts too if that's useful, thanks a lot to all who have responded! You guys are great

PS I forgot to add, do you think this could gave something to do with blowing the fuse, and how? It crossed my mind that maybe if the computer was reading the timing wrong it could be driving up the the duty cycle of the injectors or activating multiple or something crazy and out of ordinary. Just WAG but it crossed my mind.

Chrismorton10

Alright guys, so I did a little more digging and found out that the line coming from the injector fuse to the computer ( ASD Signal line ) goes straight through the pcm and powers the the field coil in the alternator and is then grounded through the pcm. Turns out the field winding inside the alternator was shorting to ground even though it was still putting out a proper voltage. I have no idea how or why it did this, but I replaced it and I have yet to blow a fuse. So problem solved! Thanks for all the suggestions!

Chrismorton10

Alright guys, so I did a little more digging and found out that the line coming from the injector fuse to the computer ( ASD Signal line ) goes straight through the pcm and powers the the field coil in the alternator and is then grounded through the pcm. Turns out the field winding inside the alternator was shorting to ground even though it was still putting out a proper voltage. I have no idea how or why it did this, but I replaced it and I have yet to blow a fuse. So problem solved! Thanks for all the suggestions!

Chrismorton10

Not sure why that posted twice😳🤣🤣

Heathguy24

Having the same issue, can you explain what you replaced exactly. Thank!

Chrismorton10

I ended up replacing the alternator. I'm not 100% sure on exactly what inside there went wrong but I'm pretty sure they happened to be some noise or a frequency issue internal to the alternator. After replacing it my problem was solved completely. 4.7l blowing the injector fuse right? If so here's a little troubleshooting trick. Unplug the alternator control connector ( little black connector on the backside top of the alternator) and give it a good hard floor down the road. Dont go far away from home because your battery WILL NOT charge as you just unplugged the wire that tells the alternator to charge the battery. But, if when you do that you dont blow the fuse, replace the alternator, if you still blow the fuse, you could possibly have a sticking injector. If you have more questions just post on here and if that doesn't seem to help then we can get an email thread going and get it solved. Best regards and good luck👍

Heathguy24

ok I will try that in the morning. Did you get a ASD relay code as well?

Chrismorton10

P1389? I think that's the one, it happened to me a while ago but I believe that was the one. The injector fuse is kinda crazy because not only does it power your injectors, it tells the computer that the asd has power and is on in addition to providing power to your alternator. Its crazy

Heathguy24

Turns out it’s the alternator... where did you buy yours? And have you had any issues since?