Hello all,

nice website i do have to say. anyway. i have a question. i have a 1997 dodge ram cummin turbo diesel. on these trucks with the diesels does the pcm control the alternator or does the alternator have its own voltage regulator? i have found rebuild kits for the alternator (denso). all i see on these kits is brushes and bearing. i guess i would like to repair the alternator if it needs it. i really dont feel like throwing my money away to the parts store since i do maint at a food processing plant. so any help would be awesome.

thanks

axe_1

 

Looking at my book here.. There is a powertrain control module(that contols the field"amount of charge") and also a shut down relay. Hope this helps

 

looks like the automatic shut down relay is powered by the PCM

 

thanks for the info. i did an isolation test of the alternator by grounding out the negative field terminal on the alternator and it didnt do a full charge like it was suppose too. i ordered a new brush kit from a parts store that deals with starters and alternators for 14.95. hopefully that does it. the only thing left is the rectifier which is 65 bucks. i think im going for the rebuilt one from O'Reillys for 162 with a lifetime warranty if the brushes dont work.

thanks

 

trying to post a schematic. looks like the field is driven from the PCM.

 

thanks for the schematic, that will help. i'll let you know what the outcome is.

later,

axe

 

well, i installed the brushes on the alternator. once i pulled the old ones out i knew right away that wasnt the problem. this charging problem all started when i started it up and preceded to drive around 30 mile trip back home. it never charged the whole way. next day i went to work and once i got on the highway, it started to charge. it only charges at a high rpm. im starting to think its the recitfier (diodes). one thing i was wondering on that wiring diagram, what kind of signal is the pcm signaling to the alternator and on which wire? im pretty close to buying a rebuilt alternator i just want to make sure its the alternator. i did the the full charge test by grounding out the negative on the field terminal and nothing happened. im guessing when the pcm doesnt feed signal to this terminal it should be charging full. and when the pcm feeds like 12 volts or so it doesnt charge. i hope im making sense on this. off i go...

 

I have a 96' CTD and on every start there is a significant delay before it charges, maybe 15 seconds and it will go up and down for the next minute or so. After that it doesn't go below 14 volts. It seems to do it when it's cold, maybe the heating grid draws that much until things get warm?

Rhino

 

yes it use to act that way too. but now when i come to a stop or the engine is at idle, the volt meter drops to 10-12 volts. the oem volt meter is right i checked it with a mulitmeter. the truck never use to do that. i always had at least 13-14.5 volts on the meter and just by watching the lights on the truck when i slow down on how they get dim and then bright again when i start off again.

axe_1

 

Just a quick thought. When you pull you altenator apart to check or change brushs. check the coil that turns (inside one). should be two pads where the brushs ride on. Check these two points.should read aproximatly .1 ohm (pretty much a dead short). Last 3 altenator I fixed had an open where the wires connected to one of those pads. Long shot but sense you have a meter and are planning to change brushs anyway. you should also be able to check the diodes with your meter. unless they are in somesort of package. anyhow they should all test the same. check them both ways. They are polarity device so they will change values depending on the way you ohm them. (position of meter leads).