Surging and lights dimming at all speeds - Chevy and GMC Duramax Diesel Forum
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Old 07-25-2010, 02:21 PM   eBay Motors  #1 (permalink)
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Surging and lights dimming at all speeds

Hi guys,
I just bought a 2005 3500hd and it has a slight issue (at least I hope it's slight). It seems that it is surging a bit no matter what speed you are going and when it does this it actuallly causes the interior and exterior lights to dim and brighten along with the surging. It is more noticeable at idle, but you can "hear" the surge at any speed. I have been reading up on it and it seems like the fuel pressure regulator could be the culprit but I wanted to hear your thoughts on the lights dimming. Do you think the FPR would cause slight dimming along with the surging? Any help would be great as we just lost our Chevy dealer in the town i live in.

Thanks!!
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Old 07-25-2010, 11:17 PM   eBay Motors  #2 (permalink)
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Welcome to the forum!

Wow I cant think of what would cause the lights to dim. The batteries hold power to prevent that.

Id have the batteries and alternator checked if it was me
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Old 07-25-2010, 11:56 PM   eBay Motors  #3 (permalink)
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Thanks for the welcome!

do you think a bad ground or other alternator issue could cause the loping or surging? The weird thing is that even at highway speeds i notice the lights dimming and coming back brighter. and also at highway speeds you can almost hear or feel the slight lope from the engine as well. I'm close to pulling the trigger on the FPR replacement, but just wanted to see if anyone else has had these symptoms first. I'll get the alternator and batteries checked in a couple days though...

Thanks!
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Old 07-26-2010, 04:01 AM   eBay Motors  #4 (permalink)
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Ground could be an issue. Something momentarily drawing a large amount of power or nearly shorting out could also cause it. Isn't the fuel pump electrically driven? If so, if there is a severe voltage change it could effect fuel pressure delivery, causing the engine change....
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Old 07-26-2010, 06:41 AM   eBay Motors  #5 (permalink)
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Ground could be an issue. Something momentarily drawing a large amount of power or nearly shorting out could also cause it. Isn't the fuel pump electrically driven? If so, if there is a severe voltage change it could effect fuel pressure delivery, causing the engine change....
D-Max trucks do not have a factory fuel pump. The fuel is pulled from the fuel tank, through the fuel filter by the CP3 pump, where it is pressurized to the injectors. That is why you must hand pump the fuel system after a filter change. Also, any leak in the filter or lines will cause the engine to fail to start or stall after starting.
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Old 07-26-2010, 08:04 PM   eBay Motors  #6 (permalink)
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thanks guys! so would a faulty fpr cause an excessive draw on the electrical system? or has anybody that has ever dealt with this surging ever noticed the lights slightly dimming? on the way to work today I noticed it surging a little even at highway speeds. does that coincide with the fpr going out? and my final newb question is should I see the voltage gauge fluctuating much when cruising down the highway? thanks guys for all your help!
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Old 07-27-2010, 04:07 AM   eBay Motors  #7 (permalink)
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I have never noticed my voltage guage fluctuating while driving. How much does it fluctuate? Does the fluctuations coincide with the changes in engine?
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Old 07-27-2010, 05:44 PM   eBay Motors  #8 (permalink)
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it doesn't fluctuate with the surging cycle, it seems to be completely random, whereas the surging is very consistent and repetitive. It fluctuates from around 14 up to 16 easily. It does seem to move constantly, never really sitting still. Is this something I could take down to an autozone or somewhere like that and have them test the alternator? I just drove the truck 1200 miles back from colorado and it doesnt seem to have any power issues or weak battery issues which i would think would happen if the alternator was bad. Could the voltage regulator be quirky on the alternator? any test i could do for that?

Thanks!
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Old 07-27-2010, 06:30 PM   eBay Motors  #9 (permalink)
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Sounds like you have determined the voltage fluctuation is a separate issue from the surging issue. I don't see fluctuations like that - either with the factory gage or with a tester - so you should have it checked. First easiest check is take it to autozone or wherever and have it checked out. Only fluctuations I have seen is when I can identify a substantial load is on/off (defroster circuit...) and then it drops when I turn it on, rises when I turn it off, and then only when engine rpm is low enough that alternator can't keep up. How long between fluctuations - seconds, minutes, 15 minutes? And since the computer ostensibly controls the running of the engine, I suppose voltage levels could effect it - unless the computer is turning a load on/off causing the fluctuation...
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Old 07-28-2010, 09:52 PM   eBay Motors  #10 (permalink)
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well I have been tinkering with it a little today and have some more details... I took it to autozone and had them check each battery by themselves and they both checked out good. when the guy left the negative hooked up on one battery it came back bad but when he tested the battery without the ground hooked up it came back good. kind of odd, but im not sure how those testers are supposed to be used (while hooked up to the engine or not). So then we moved on to the alternator and it came back while revving to 2000 rpms as 13.78 volts, 201 amps and the diodes were good.

The thing i noticed after hooking the batteries back up before the alternator test was that when i ran it to 2000 rpm and held it there and then let it back down to idle, the surging was gone and the volt gauge was super stable. Even after driving to a friends house it stayed super stable with no hint of surge.

Unfortunately soon after, i went for a drive and it came back just like before. The surge and light flicker during idle is about a 1.5 to 2 second surge cycle, but as soon as I apply ANY throttle, the flicker and the surge kicks to about a .25 second cycle (much faster). As soon as i let off the throttle to idle, it drops back to the slow surge/flicker cycle.

So now I lean more to a possible electrical problem vs. the FPR going out. Is there anything in the motor or drivetrain that is an electric device that is cyclic like that? It doesnt seem to match rpms (like it doesnt increase at the rate the rpms go up) but it does flicker faster at any throttle position then slower at idle...

I know, I know, lots of info and questions, but it does feel like I'm getting somewhere! Thanks again for all your advice and help!!!
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