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Duramax First Generation: 2001-2004 (LB7) Discuss the first generation (2001-2004 LB7) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 09-02-2019, 02:28 PM   #1 (permalink)
tammybrian2
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2003 fuel rail pressure and voltage fluctuation

i put this post in the eletrical forum but got to thinking maybe it might be something else causing this issue:

"2003 lb7 198k miles. the voltage gauge and the lights on the dash fluctuate. batteries are a year old. voltage when truck is off: 12.75 when truck is running, voltage constantly fluctuates between roughly 14.2 to 16.5. rev up truck to 2k rpms the gauge went up as high as roughly 17.5v according to the gauge. any thoughts on what might be causing this? thanks --Brian"

i put my scanner on the truck and saw that the fuel rail pressure, at idle, is running roughly between 4800 and 5500 psi, the graph on my scanner constantly jumps up/down between the two. accelerating narrows the gap in the FRP on the scanner.

again, the voltage is jumping between 14.2 and 16.5v.
could this be a fuel pressure regulator issue?
any ideas would be appreciated--Brian

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Old 09-02-2019, 04:17 PM   #2 (permalink)
davester
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16.5V seems high, but I would suggest checking what the voltage at the alternator is with a voltmeter.


As for fixing the issue, it could either be the alternator itself, or a poor power/ground connection.

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Old 09-03-2019, 04:16 PM   #3 (permalink)
tammybrian2
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voltage at the alternator is constant up and down 14.7 to 16.2.
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Old 09-04-2019, 01:37 AM   #4 (permalink)
davester
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fluctuating voltage, then I would say it's most likely the alternator
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