Alternator discharging at 2,000 rmp????

[hydro2]

I recently bought a 2001 Chevy Durmax. The alternator is discharging at about 2,000 Rpm. It charges fine while the truck is at an idol or you are driving along. If you get into the accelerator and the RPM s come up, then the volt meter drops down to around 12 or so and the headlights dim if it is at night. Strangest thing I have ever seen. I would appreciate some advice on where to begin. The alternator tests fine as do the batteries.
Thanks for the help.

[Duramaster]

I can say that the belt tensioner on the 2001 DMAX engine is JUNK! The tensioner tends to chatter which allows the belt to squeek. This is usually only noticeable at idle though.

[chipper]

Could be brushes hanging up or a bad regulator.

[hydro2]

I thought it might be the belt tensioner . It is moving a good bit at idle and seems to be very week when I put a ratchet on it. The alternator is putting out about 70 AMPS. I don't know if that is enough or not. I believe that it should be putting out at least 105. Crazy thing is, when I turn on the heater motor, the voltmeter does not show a discharge until around 2,200 RPM instead of 2,000. It seems to do better with a draw on it. I have never had a vechicle get worse at higher rpms. How many amps do the injectors draw?
Thanks for the input. I will post the solution, when I find it.

[hydro2]

At this point I am wishing I did not give up my old 460 Ford. It was a pain, but this??? Had that truck for 22 years. Don't think I will have this one that long. We are not off to a good start together. :mad:

[JohnC]

Take another look at the tensioner. I've seen slipping belts do this. They can't hack the higher RPMs.

[hydro2]

Took the truck to a chain auto parts store on Sunday becuase my usual altenator guy is not open Sun. It is a little ma and pa shop. The chain store tested it and said the altenator was fine. Took it to my regular guy today after work and guesse what. It was toast. Rebuilt it and it is now charging fine. Had it rebuilt for $113.00. He even took it out and put it back in. Can't get that service at the chain store. Still not sure about this Durmax. Sounds like the injector failure might be a pain. I mean new injectors at 100,000 miles. I have a buddy that has 350,000 on his Cummings. I have another buddy that got 325,000 out of his 6.9 Ford before injector trouble. Makes me glad I spent big money on this Chevy.

[Duramaster]

6.9.................................... Low pressure fuel system like old 6.2/6.5. As far as the cummins I'm guessing it is low pressure too. DMAX = not low pressure. 5k PSI or so at idle and 23k+ at WOT depending on engine (LB7, LLY,LBZ,LMM).

The higher pressure fuel systems require a little more care and finesse when it comes to the maintenance of the fuel system. And that's not just the DMAX. I'm sure that any of the high pressure fuel systems are going to have their quirks when it comes to fuel system maintenance.:cool:

[hydro2]

Yea the old 6.9 Navistar were great motors. No injector problems there.