2nd Gen Non-Engine/Transmission alternator troubles

[Piersol]

Periodically, over the past year, my "gen" light has been coming on after I start up the truck. The volt meter reads about 12 volts when this happens. It usually reads about 14 volts. I tried unhooking the grid heaters tonight but the volt meter still reads 12 and the "gen" light is still lit. Most of the time everything is fine. This has happened three or four times in the past year. If the alternator is on its last legs would it do this. I always thought an alternator either works or it doesn't. I'm afraid the pcm is bad because it is not regulating voltage correctly. Everything else electrical works fine though. Any suggestions? I took the alternator to Auto zone and the guy tested it on the truck with his tool. At first , with the truck working fine and no gen light lit he said the alternator was marginal. I figured I would replace it. When he went to look up the alternator in the computer he said it was WAY low. I'm assuming he looked up the amps on a diesel and it was significantly more that a gasser. Well, I put on the new alternator and found the pulley they gave me was about 1/8 inch too narrow and the belt rubbed against the alternator so I returned it without seeing if it made a difference. I kind of lost confidence that they knew what they were talking about. Just checked voltage with a meter engine off- 12. 68 volts engine on-- 12. 46. Also I smell something electrical. no fires or melted wires though.

 

[C. Harlan]

sounds like a PCM... . a friends went out, and his truck would barely run when it was on, but when you turn the key off, the batteries would be fine. I think they go for about 300 or something like that, so it shouldnt hurt too bad. But that has all the tell tale signs of a bad PCM in my opinion.



-Chris-

 

[Piersol]

I took the alternator off today and had it tested. It read 4 volts. I guess it's shot. Put a new one on and volts are up to 14. 2 while idling. Batteries read 13. 1 with the truck off. if you get an alternator from autozone or advance check to make sure the right pulley is on it. I went through 4 alternators and only one had the serpintine belt pulley and even that was too narrow. i had to put my own pulley on the new alternator.

 

[bmoeller]

Our alt. pulleys have 8 grooves, not seven like what comes on the Autozone alts. They/you need to swap them over. Be careful removing them. The idiot at AZ that tried removing my old pulley damaged it. It is pot metal. I found a new steel pulley at http://www.buesings.com/ (Went to the store since it isn't that far from me. ) AZ reimbursed me for the cost of the pulley.