Engine/Transmission (1994 - 1998) Charging Gremlin

[crabman]

Started truck and voltmeter showed 12V and did not move upon driving, usually shows 14V. This is what I did:

1. Pulled both batteries and cleaned all connectors and under batteries. Reinstalled, started engine and still 12V on voltmeter.

2. Pulled Alt. and benched checked. Checked out good. Reinstalled Alt. , started engine and still 12V.

3. Did the on-off key thing. I did this 3x as I wanted to be sure I copied down the correct numbers. The numbers are 3, 4, and 2. Checked my Powertrain Diagnostic Procedures book and did some tests and everything pointed to the PCM. So I decided to take the truck to my local repair shop and see if they could read the PCM troubled codes with a DBR. I started the truck and the voltmeter showed 14V!! I have put 50 miles and truck with several start-ups and all is OK.

Anyone have any ideas, thoughts, hunches, suggestions, etc. ?

TIA

crabman

 

[PUMPERDUDE]

If its the original altenator ,I'd put money down that its toast. I just changed my 95's altenator about 2 months ago. I got a couple of intermitent check engine lites over a period of about 2 weeks. Voltage would fluctuate every now and then. Brought it by Auto zone for a free check and it was weak. After I pulled it ,I did a little inspection and it was quite worn @ 223 k miles. Glad it wasn't the PCM$$$$... . The code I got was #41... An open or shorted condion detected in the generator field control circuit... Good luck with it

 

[bmoeller]

Did you check the alternator fuse in the PDC? It is the one held down with 2 screws. If it is blown, it will only show 12v.

 

[Howard Durand]

Since it returned to normal operation, I would watch it for a while and see what it does.

It may be that the PCM needs to be re-flashed.

 

[crabman]

Pumperdude,

The Alt. was removed and bench checked for at least 3-5 minutes and I was present while the tech. did the tests. This repair shop is a auto electric shop who specializes in electric repairs. The tech said that these alt. usually last 175K at least and I have only 128K on mine. I also did not get any "check engine" light, it just stopped charging.



bmoeller,

I checked the fuse in the PDC. Sorry, I forgot to mention that is was one of the first things I did. Anyway, the alt. started charging again thats why I posted. Gremlins!!



Thanks for the replies!

Today, I am going to have someone read the codes with a DBR and clear them.

 

[JGheen]

For someone who is electronically declined, please explain the following -

What is the PDC?

What is a DBR?

And I'm confused as to what the fix was on your truck, Crabman? You mentioned the tech had checked the codes in your PCM, but what was reset or fixed to give you the 14V back?? Does clearing the codes just fix all the issues?



Thanks, Joe

 

[Dan_69GTX]

PDC - power distribution center - located under the hood

DBR - Scan tool from the dealer used to communicate/reflash/etc with the ECM (Electronic control module).



No fix to the truck - it is just possessed and started working on it's own.

Clearing codes fixes nothing, except maybe makes the check engine light go off. If you clear the code (erase them from memory) and a code shows back up - you know that the error/problem reoccured.



Dan

 

[mullady76]

I have a similar problem. At idle/low rpm the needle reads 12V, when I hit the throttle it jumps to 14V and I hear a hiss come from the speakers. At night the headlights are dim regardless of rpm. I know I have to get under the hood and start testing but I have very little time to do so.

 

[JoeBioDiesel]

They all don't last 175K. Mine went at about 100K. The brushes were completely worn, and the rectifier was melted... not worth a rebuild. I replaced it. Mine also worked intermittently before it died.



Joe

 

[JGheen]

Yeah, my alternator had started to go out around 130K. Noticed lower voltage readings and just decided to turn it in for a reman.

Weird thing was when I put the new one on, it got REALLY hot when I first fired it up. I mean so hot I couldn't keep my hand on it for too long. Not sure why it did that, but it doesn't get hot anymore and runs fine. Anyone have any idea as to why it got so hot on the initial fire-up? I was thinking maybe the battery or even both of them, were so drained of power that the alternator was having a hell of a time juicing them back up. I am not very electronically inclined, but that was my assumption.