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Discussion Starter #1
My truck is doing soemthing that seems odd on the first startup off the day, it starts and the votage guage jumps up to about 10-11 volts and then just sits there for about 30-40 seconds, then it jumps up to a touch over 14V and acts just like i would expect???? Has anyone noticed this, or is my truck fugged up? It only seems to do this on te first start of the day than acts normal all the rest of the starts afterwards??
 

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No problem, glow plugs create a massive drain on the electrical system and it takes several seconds for recovery. Edited by: FILO
 

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Mine does it on cold and hot starts. For the first 30-45 seconds the volt gauge reads 9-10 volts and the lights (at night) are dim. After that the gauge jumps up to 14-16 volts and stays there until shut down.
 

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My '03 does the same, and I believe all of the DMAX's do it. As FILO mentioned, its the draw caused by the glow plugs.
 

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Discussion Starter #5
OK i guess if others have the same thing then its OK, I find it hard to beleive its the plugs doing it though, i mean mine is like a light switch when it goes form 10 up to 14+v, it does not slowly get there it just sits at 10V for like 30sec then boom it starts to move and its up to 14+V within 2 seconds, seems like if it was from excessive draw from the plugs that it would climb in a linear type fashion up to 14V not jump up out of the blue from 10-14V??
 

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If it works like my old Mercedes, the glow plug relay does not open up immediately at start up. Rather, it is a timed relay and the glow plugs stay on even after the engine is running until the relay times out. So what you are seeing is consistent with a timed relay.


I have a voltmeter on my 20 year old Mercedes and it behaves the same way.
 

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Mine is not a sudden jump...but a more gradual climb up to 14 volts. Maybe my voltmeter is just a little lazy.
 

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Mine's the same, gradual climb over a 10 second period to 14v.... Been doin' it since it was new. No worries.......
 

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I believe it's the air intake heater grid that pulls the most power, and IIRC the PCM is in control of alternator voltage and ramps up the power slowly to protect the electronics from voltage spikes.
 

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My 03 is the same way.. takes about 30 seconds or so for the voltage to climb, then takes 3-4 seconds to climb to 14v. I figured it was the combo of the starter, glow plugs and any other stuff needed to start this thing that draws the battery down. Been doing it since day 1.


Bob
 

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Discussion Starter #11
Sounds good as long as others have the same thing i can beleive it!!!!


Thanks for the info!
 

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Mine is the same way. I used to have one of the diesel Oldsmobiles in the 80's and it had the rally cluster gauge package in it instead of idiot lights. As the relay for the glow plugs kicked in and out to help the engine warm up, not only could you hear it clicking, but the draw on the electrical system was fantastic. I don't know how the glow plugs work in the Duramax in comparision to how the old Olds worked, but I've got to believe the draw people are experiencing, which I am too, is related to startup of a cold engine and the glow plug system. Olds used to run the glow plugs intermittently even after the engine was started to help with warmup, emissions, etc. I've noticed it with mine since day one. It isn't the first start of the day that does it, but seem on mine to coincide with the wait light.
 

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gsxr1216


It's working properly. I believe they had many charging system failures
in the prior (6.2-6.5) systems that feed the glow plugs while the engine runs. After it cycles and draws from the battery the first time the system is only then allowed to "catch up" without the added voltage drain
. I Am sure dmaxalitech could answer this correctly if I haven't.
 

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They all do it, nothing to worry about. Just the glow plugs, fuel heater and air intake heated pulling allot of volts and takes a while for them to turn off and then the alt. starts charging the batterys again.
 

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I also have that problem but it also does it when i let off the gas pedal. The lights dim and the voltage meter falls down some and then goes back up. I talked to the dealer and he said it has to do with the fuel system and that they all do that. I have been in others and they did the same thing. It is a pain in the ass to explain to who ever rides with me at night why the lights dim, I just tell them it is a chevy thing
 

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This question was asked way back when the 01s came out. Someone answered that there was a built in delay on the alternator cut in. Just by the way mine acts, I relieve that. After reading that, I tried mine without waiting for the start light to go out. Exactly 30 seconds later it went from 9 volts to 14 in less than three seconds. There is no way that both batteries were/are down to 9 volts. It is also not normal for lights to dim anytime unless the regulator/alternator is bad. Later! Frank
 

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There is a GM bulletin on these issues. The computer controls the output of the alternator , at start up , and also when engine rpm drops. There have been lots of complaints, however its not a dmax issue, but does it in many GM vehicles since 1999 I am told. (cars and trucks.)


As for charging system problems on 6.2 / 6.5 I was told that heat and vibration were he main causes of any alternator failure. On both my 88 with serpentine , and 85 with 3 belts I could expect a new alternator every 2 years - or 100,000 to 125,000 miles.





Again, THANKS to evryone who made the Northeast gettogether a success !
 
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