VP 44 voltage issue

[Tractorman]

3 hours ago, webbrenda said:

Checked the big wire at back of the alternator and it’s putting out around 22 volts and blew the 140 amp fuse.

 

Part of your statement here is normal.  What is not normal is the blown 140 amp fuse.  Need to find out what caused that right away.  It is not likely that the alternator caused that fuse to blow.  The maximum output of the alternator is about 130 amps.  One thing that can and has happened to people is accidental momentary grounding of the alternator output terminal.   The 140 amp fuse instantly blows.  You have been doing a lot of electrical work on your truck.  The 140 amp fuse could have been accidentally shorted to ground right at the PDC location.

 

Because the 140 amp fuse is blown, It is now normal for the alternator output voltage to be higher than normal (22 volts) because the current has no where to go (the 140 amp blown fuse}.  The internal regulator (inside the PCM) is sensing that battery voltage is low (which it is) and it is telling the alternator to increase output.  That 140 amp fuse is how the current gets from the alternator output to the driver side battery. 

 

So, things may not be as bad as they seem.  The alternator may be fine. 

 

Congratulations on your success with getting the engine running without codes!!

 

- John

Edited May 1, 2023 by Tractorman

[webbrenda]

Thanks again for your time and knowledge. I assumed after it blew the fuse it must have something to do with the harness but I checked the blue and black wires from alternator to corresponding pins on PCM and they are correct and show good continuity.  Everything was pointing to voltage regulator in PCM I thought( before reading your response about current having nowhere to go)  so I sent my boy to town for an external regulator and just got done wiring it in and still have 22 volts at alternator.     I also assumed the high output was what caused the fuse to blow.  Any ideas what would have caused it to blow?  I replaced alternator earlier in this process because it was showing low voltage at the gauge and I was grasping at straws and it did test bad at O’Reillys.   I have had the truck running off and on by jumping pins on the relay and can’t say for sure when the fuse blew.   With the only thing in that circuit being the alternator and battery and if the high output didn’t cause it I’m lost as to why it blew. 

Just reread your response and I guess it is possible that I shorted it out when I had the PDC box up and out of there tracing wires.  I am sure I am overthinking some things.  Every time I find something and fix it something else rears its ugly head.   Couldn’t find a fuse anywhere today but will have one tomorrow and I’ll replace and see what happens.  Thanks again 

[Tractorman]

Before installing the 140 amp fuse, connect an incandescent test tight  - one end on the alternator output and the other end on the battery side of the 140 amp fuse holder.  If all the diodes in the alternator are okay, the test light should not light because there will be no path to ground.  If all is well, install the 140 amp fuse.

 

The 140 amp fuse is not there to protect the alternator - it is there in case a direct short to ground should occur in the alternator or the alternator output wiring.  If that fuse was not there, an engine fire could easily start from the heat generated by the overloaded circuit from a seemingly endless supply of energy from two large batteries.

 

- John

[webbrenda]

John.  
replaced the fuse after testing as you suggested. All is well.   I’m only getting like 12.8 volts from alternator but I just ran the truck for a few minutes.  I’ll drive it and let it get up to temp and check it again.   I have no codes and truck runs well.  The only odd thing now is the WTS start light is delayed a few seconds and it wasn’t that way earlier in this process. And the LP doesn’t run after bump start but it does come on for a second after the WTS and it runs after it starts and I’ve got 15psi.     I can’t thank you enough for all your input and help with this.  

[webbrenda]

Bad alternator off the shelf.  Resolved and everything is back to normal.  Damn what a process.  

[Tractorman]

On 5/1/2023 at 7:26 PM, webbrenda said:

I have no codes and truck runs well.  The only odd thing now is the WTS start light is delayed a few seconds and it wasn’t that way earlier in this process. And the LP doesn’t run after bump start

 

Did these two situations resolve themselves?

 

Things must be looking much better now that you have a truck that you can drive again.

 

- John

[webbrenda]

No they didn’t.  I posted the last update a little too soon.  After I got the alternator replaced, the first time I started it the WTS light came on almost immediately( maybe a second or two ) after key on and truck started right up.  Thought I had it.  But after putting everything else back together and finishing mounting fuel pressure gauge and boost gauge it does take a few seconds( 3-10) for the WTS and the LP doesn’t run with bump start.   At one point after the the harness and ECM both worked the way they should.  Getting a little lost on the sequence of events.   Should I send the ECM in or do you have any other ideas what would cause it?   Not sure why it worked at first several times but now it doesn’t. 

[Great work!]

The ECU stays on for about 30 seconds after you turn the key off.

 

So wait awhile then turn on key and check the WTS light.

[Tractorman]

 

Pin #15 and #35 provide power to the transfer pump.  One is for run mode and the other is for crank mode - not sure which is which, but it doesn't really matter.  The wires are both connected at splice #160.  That  splice is a potential problem area, but I don't think it is your problem because you are having two problems simultaneously - no fuel pump operation in bump start and a delayed wait-to-start light.  It could be that your delayed wait-to-start light is not allowing the ECM to trigger the bump start fuel pump operation. 

 

Ditto on what @Great work!says.

 

- John

 

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