Engine/Transmission (1994 - 1998) Voltage wont recharge after startup

[CumminsFarmer]

Hey guys,



I have a friend with a '97 12-valve just shy of 300k miles. He just put a new alternator on a couple weeks ago. Old alternator bench tested BAD, new alternator bench tested GOOD. About 50% of the time after startups now his voltage will not move up to the 14 mark on the gauge for a really long time, sometimes 5 minutes! His alternator is putting out 14. 1 volts at idle, however his batteries are not in the best shape. Grid heaters seem to be cycling normally, but not so sure when the voltage is down. I think all connections are tight but not sure, as I didnt do the alternator swap and we checked it in the dark. The other 50% of the time his voltage will build back up after a few seconds just like normal. Any input appreciated!



-Cole

 

[Dave M]

I have a 97 also and went thru replacing my PCM and finally the crank position sensor to fix my alternator not charging at all. I would check and clean the battery connections and verify grounds. The PCM supplies the charging function to your alternator but the pcm will not work without the CPS working too. It doesn't sound like either of these are your problem but just something to keep in mind.



My guess would be your batteries are weak. Take them to an auto parts store and have them checked. I would replace them as a pair.



Good luck,

Dave

 

[Vaughn MacKenzie]

I second checking out the batteries. I bet one has a partial short. . . draws a lot of charge current (keeping voltmeter down), but charges slowly & has poor capacity. Might be what helped kill the old alternator. . .

Vaughn

 

[GAmes]

To rule out the grid heaters disconnect one small wire from each relay. They pull straight off. A stuck relay not only will keep the volt meter needle low, it will kill the batteries and the alternator over time.