Well I just bought a new(to me) 07 5.9l cummins mega cab 4x4 auto.

When I first start it up sometimes the battery metter will drop way down to the low has mark, I thinks that about 10 amps? And if the lights are on it will dim and then build right back up to normal, if I give it gas it will fade also and then come right back up.

I went to the local dealership and just asked the service guy what it might be and how long it would take to check out since its under warranty. he said I think diesels do this. i didnt even blink just turned around and walked out. Im going to run it by a DIFFERENT dealer this week and see what they say. Is this a bad alternator, battery, or seomthing worse?

Sorry for the long post. Thanks tho.

 

It's the grid heater cutting on and off. This is normal.

 

I think that is normal. It is the grid heater cycling until it reaches temperature. Mine does the same thing.

 

See above thread....


Voltage Drop / Lights Dimming on Cold Start

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It's time to "sticky" this one at the top of the forums again.

If this describes what you're experiencing when lighting off the Cummins on these frosty mornings,.......
Don't worry, it's normal.

The Cummins uses a pair of 12 volt grid heaters in the intake tract
(imagine two large toaster elements glowing bright red)
that preheat incoming air for easier combustion.
The Ford & Chevy use glow plugs inside the combustion chamber.
As the relay cycles the grids on & off, the large amp draw causes the volt meter reading to drop, and the lights to dim when the relay turns on the juice.
The relay timer will turn off the heaters when the intake temps hit a preset limit, or when the vehicle exceeds a preset MPH (usually between 15-25 mph). edit


Don't panic
.........just another of the experiences you can chalk up to being a member of the Cummins Club.

 

so The cummins does not have glow plugs?

 

No,it does'nt have glow plugs.I think you really need to take time and read your owners manual!