Need help ASAP, truck is dead!

[DaveBen]

Do you have an electrical drain that runs all of the time? Like an Amp?

 

[Farmer Rock]

It only seems to be while it's running that the batteries get drained. A few minutes after startup the voltage just drops fast and the truck dies.
Batteries are charging now, then I'll give a shot again.


Rock

 

[gnathv]

I went out and took readings on my 97. I believe the alternators are the same. Battery out is the lug on the back. I checked it with the engine off no key in ignition, then I started it and took measurements again. While the glow plugs were on the battery read 11.7 After glow plugs cut off 14.5. These are the voltages I see, hope this helps. If your alternator isn’t putting out, the voltage will dive quickly. You’re running electric fuel pump, PCM, and what I think is probably the biggest draw besides glow plugs the IDM.

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[gnathv]

I know you told me the light flickered once. Does the light come on steady with the key on and the engine not running? The light bulb is part of the charging circuit.

 

[Farmer Rock]

I know you told me the light flickered once. Does the light come on steady with the key on and the engine not running? The light bulb is part of the charging circuit.

I don't remember seeing the battery light come on, even with the engine off and key on. I thought that was strange

I went out and took readings on my 97. I believe the alternators are the same. Battery out is the lug on the back. I checked it with the engine off no key in ignition, then I started it and took measurements again. While the glow plugs were on the battery read 11.7 After glow plugs cut off 14.5. These are the voltages I see, hope this helps. If your alternator isn’t putting out, the voltage will dive quickly. You’re running electric fuel pump, PCM, and what I think is probably the biggest draw besides glow plugs the IDM.

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I really appreciate you taking those readings. I'm starting to wonder, if it's not as simple as the batteries, maybe the GPs are stick on? I noticed they run for quite awhile.
Batteries should be about done charging, I'll give it a shot again.


Rock

 

[DaveBen]

It only seems to be while it's running that the batteries get drained. A few minutes after startup the voltage just drops fast and the truck dies.
Batteries are charging now, then I'll give a shot again.


Rock

"While it's running that the batteries get drained"???? What are the voltage readings when it first starts and just before it dies?

 

[trackspeeder]

Have the batteries tested.
If the voltage drops that fast there is a dead short someplace.
What ever is failing should be extremely hot.

 

[Farmer Rock]

"While it's running that the batteries get drained"???? What are the voltage readings when it first starts and just before it dies?

That's correct.
After charging batteries, they both tested at 12.7v, there at around 10v before it dies.

Have the batteries tested.
If the voltage drops that fast there is a dead short someplace.
What ever is failing should be extremely hot.

I had the batteries tested yesterday when I brought in the alternator. Tested good, but drained.


Rock

 

[Farmer Rock]

So I charged up the batteries and drove it home so I can work on it. The batteries were at 12.3v when I left, and 11.2 when I got home(15 minutes).
It just seems like the alternator isn't turning on. Does anyone have a diagram of the 2 activation wires that plug into the alternator?
Also, I disconnected the GP, and it didn't cause any difference in voltage, so I guess I can rule that out.


Rock

 

[gnathv]

If your battery light is blown I don’t think it will charge.
Check fuse 29. That runs charging light and airbag light.
Here are the voltages you should be seeing on those 2 wires at the alternator and the output to your batteries.

 

[catbird7]

I'm right there with you regarding learning about all this electronic stuff on these engines. One of the recommendations when the alternator isn't charging says to check fuse #45. Also recall mentioning fuse #6 ( I think.)

 

[Farmer Rock]

I'm right there with you regarding learning about all this electronic stuff on these engines. One of the recommendations when the alternator isn't charging says to check fuse #45. Also recall mentioning fuse #6 ( I think.)

The diagram I am using ( from the interwebs) doesn't go higher than fuse number 30. Do you happen to know of a better diagram? I have no idea where fuse 45 is now.
Thanks


Rock

 

[Farmer Rock]

If your battery light is blown I don’t think it will charge.
Check fuse 29. That runs charging light and airbag light.
Here are the voltages you should be seeing on those 2 wires at the alternator and the output to your batteries.

That's really great info, I am definitely going to check the battery light out. I I tested it by grounding the wire to it, and it never came on. So if I understand correctly, if the bulb is bad, it won't conduct electricity to the alternator? I hope it's that.
Thank you so much, I really appreciate your help.


Rock

 

[Farmer Rock]

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I never would of thought the battery light ran inline to the wire that activates the alternator, but looking at this, I see how a the battery light could act like a burnt fuse.

Rock

 

[TNBrett]

Have you tried disconnecting the glow plugs and intake heater from their relays yet?