Engine/Transmission (1998.5 - 2002) Well it wasn't the alternator - what could it be??

[T Smith]

I'm having an electrical problem and was wondering if someone could help please: The truck is a Y2K (remember that?) 2500 SLT+ quad cab short bed 4x4 with 6 speed trans.



Here's the deal... driving to work earlier this month with lights on, defrost on high, heated seats on, I got a chime so scanned the guages and the volts had dropped to zero. Shut everything down and restarted and charge was above 12, but wouldn't go above 14 (usual on my guage) until was driving and had turned off high beams and fan (of course no heated seats).



At initial start the guage shows @ 12v, you can see the heater grid drop it down, but after it finishes cycling and start driving, it will get up to 14+v on the guage. If I turn on the lights it's mostly ok until turning on the high beams, fan, wipers, etc. Then it will drop off and sometimes will go below 12, get the chime and down it goes to zero. It always seems to show some charge after restarting.



Batteries appear to hold a charge, I have put the charger on and at other times when well charged (no electrical draw) the guage shows half way between 12 & 14 at start up.



Thought for sure it was alternator since all alse seemed fine. Changed the alternator and it's doing the same thing.



Any ideas on what's up?



Thanks for the help.



TSmith

 

[icman95]

Did you put a voltometer on it while running to actually check the output of the alt? That way you can check to see if the dash gauge is actually right. If there was an electronic problem that was fooling the dashboard, the alt may not be the problem and the dash might be lying to you. Maybe a loose wire somewhere else?

 

[georgej]

Clean the battery posts and check all grounds for good contact. If the batteries are over 5 years old they might be toast. If this doesn't help I've heard the ECM can give charging problems.

 

[Huff N Puff]

If you are,loading the alternator in this manor at Idle

It is normal. The alternator can only carry that kind of load at 2000rpm. If you are loading it and its at 2000rpm or more and the voltage is still low under 13volts you have a problem.

 

[KLockliear]

Sounds a lot like my symptoms... I changed the alternator, PCM (because that's where the regulator is) and trouble shot the whole system.



Turned out, the pins in the field plug on the back of the alternator were loose and breaking connection to the alternator.

 

[CumminsAholic]

Mine did that. I ran it for a year like that. Lights would dim when I let off the throttle if I had the heat on. I had the alternator rebuilt, it lasted 3 days and did it again. The negative diodes were blowing out. I had previously cleaned all the gounds so I took it back to the rebuilder and he rebuilt it again, I rechecked the grounds. I charged the batteries before I installed it and haven't had a problem with it since. But my ecm went out about a month after this... coincidence? I dunno. I know the pcm controls the alt, but still. Anyways long story short, I had the first replacement go bad right away, so could you. It's so nice now to have the heat on high, radio blaring and the lights stay bright even at an idle.

Corey

 

[T Smith]

Found out it WAS the alternator...

It was the alternator after all.



After driving a bit and the batteries got charged up, everything seems to be working fine now.



Huff-N-Puff is right about the low RPM, at least when the heater grids are on for my rig. They sure take the power but once they're off line the guage shows steady > 14v charge regardless of lights, fan etc. even at idle.



Thanks for all the help, glad to get that straightened out!



TSmith