6.7L Cummins Forum

I'm an old school type of guy so the first time it got cold outside I thought I had a bad zener diode in my alternator and thus the voltage fluctuations at idle but now I find out it's completely normal and the following is why.

The PCM, or ECM receives a voltage input from the generator (5) and also a battery voltage input (7) from the TIPM (Totally Integrated Power Module), it then compares the voltages to the desired voltage programed in the EVR (Electronic Voltage Regulator) software, and, if there is a difference it sends a signal to the generator EVR circuit to increase or decrease output. It uses a Pulse Width Modulation (PWM) to send signals to the generator circuitry to control the amount of output from the generator. The amount of DC current produced by the generator is controlled by the EVR circuitry contained within the generator.

So unlike my 82 Corvette that has the regulator built into the alternator the Cummins 6.7L is software regulated, pretty trick.

Oh by the way if you're wondering what's causing the fluctuations in the first place it's the post-heat cycle of the intake manifold heater system. The

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2007.5 Dodge Ram 3500 HD,QC, 6.7L Cummins, 6speed Auto, 4X4, Bighorn Edition.
Click for installs: Carr Steps PML Diff Cover Edge Juice with Attitude Volant Intake Hankook ATM RF10

Thank You for the info I was coming online just to see if anyone else had had this problem. HAD HAD? LOL Boy this one had me thinking that I already had a problem.
You sure are on top of this one Squid again Thank You

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Winger
2008 2500 Silver 4x4 6 Speed Auto Big Horn Edition Volant CAI Magnaflow Muff Edge w/ Attitude
1990 Honda GL 1500 Wineberry 125,000 Miles
2005 Honda GL 1800 Candy Blackcherry 50,000 Miles

I know the feeling. When I had it happen to me I was freaking because it was happening all night long every time I started the truck whether it had sit for 6 minutes or 60.

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2007.5 Dodge Ram 3500 HD,QC, 6.7L Cummins, 6speed Auto, 4X4, Bighorn Edition.
Click for installs: Carr Steps PML Diff Cover Edge Juice with Attitude Volant Intake Hankook ATM RF10

So how far does your voltmeter go during the load-on cycle? mine is to the low side of normal, was hoping this is normal and not early sign of dying batteries... I was also worried and thinking I had a voltage regulator problem.. thanks Squid!

I was thinking the same as all of you guys... starting to panic a little bit, so thanks for the info, BIG HELP.

Mine goes all the way to the left.

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2007.5 Dodge Ram 3500 HD,QC, 6.7L Cummins, 6speed Auto, 4X4, Bighorn Edition.
Click for installs: Carr Steps PML Diff Cover Edge Juice with Attitude Volant Intake Hankook ATM RF10

It's pretty common now for the 'puter to control the alternator,but a wild swing is not. Mine would do the wild swings until I was a couple of blocks down the road. Yesterday it didn't recover,I charged the batteries so I wouldn't have to walk or wait for the auto club tow last night. Fine in the morning,12 with the check gages again this afternoon.I think I have a problem.

its the nature of the beast. as squid explaned intake manifold heater cyceling will hog 90% of the trucks voltage intill the temp sensor in the water manifold reaches a certain temp. they have had this set up since 1988. sure beats having to deal with glow plugs.

Yes thanks Squid for clearing that up. My goes all the way to the left as well.

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08 6.7L engine NOT STOCK, 6 speed auto, 2 inch leveling kit with 285/70/17 Toyo Open Country AT, 3.73 rear end, SLT package, 22MPG@70MPH , RBP fuel additive.