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12-28-2007, 07:31 PM
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Cummins 6.7L Voltage Fluctuations when cold
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 number of cycles and the length of the cycling operation is controlled by the engine control module, this time will not exceed 150 seconds. The needle should then stabilize at the approximate operation point. • The cycling action will cause temporary dimming of the headlamps, interior lamps, and also a noticeable reduction in blower motor speed which is what I was seeing.
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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 
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02-24-2008, 08:56 PM
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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
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02-25-2008, 05:28 AM
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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
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