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Discussion Starter #1
I've started noticing some roughness in idling at stop lights. Have 26K on an '03 Dmax. No surge and the roughness is not bad but noticeable and does not occur all the time, occurs more frequently when cold. I noticed on another site some posts concerning this maybe 5-6 months ago but never saw any followup posts about whether it resolved, worsened, or idenitification of the cause. Anyone else experience this and determine the cause?
 

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When was the last time you changed your fuel filter?
 

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I get the same thing. It's not a lope it just shakes a little at idle in gear. Doesn't always do it. Does it with a brand new filter. Been doing it since about 10k, now have 21k.
 

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Discussion Starter #5
I have changed the OEM fuel filter at 10K and 24K, and had the CAT pre-OEM installed at about 25K. Maybe I got a tankful of poorer quality diesel if thats possible. But usually fill up at the same truck stop. The only thing different is that I only used 2 oz of Total Power with current tankful where I usually use 8 oz per tankful.
 

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I have the same issue, but the truck still runs good and no one seems to know so....


I have had it since day 1, kind of shakes the truck a little more than any other Dmax I have had or been in. Smooths out above idle, does it in or out of gear. No codes and the last time I checked, the injectors had a good balance rate. Additive since day 1 and still does it after changing the filter. Have I eliminated everything?


The only thing I can think of is air....
or maybe the pump? Like I said, she stills runs good, so until something happens.....


George
 

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Hmmm


Didn't think about it being air. Maybe. Would be interested in seeing if someone that has this condition got rid of it with a lift pump.





Chris, did yours ever idle rough??
 

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Mine does it when cold,it also has a little surge with it.Seems to run better when its hot.Started couple thousand ago while towing,have 9800 now.
 

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My 01 also sometimes give the truck a little shakey when at a light. No issues though. As soon as I go off idle it's gone. Most of the time it idles perfectly smooth.

The problem with the Duramax is it's so smooth and quiet we get nervous at the slightest change.
 

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I have found mine has a little rough idle,but only when the air cuts in than smooths out when it cuts out.Remember the air works when switch is in defrost or defrost/floor with the fan on even if the air button is not pressed.Mine has done it for about 6 months now doesn't seem to be any worse or better so I just live with it
 

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Well just changed my fuel filter today and guess what,no rough idle.You would think I would be happy but nooooo.Second filter change cut open filter after 8000 miles and found it to be black from top to bottom, rust on the inside of housing and small amount of rust on the bottom(but no water observed in filter) .The first filter change at 16,000 miles 2/3 black and no rust.Now the question is poor fuel,wrong additive(stanadyne every tank)poor quality control on filter, or combination of any or all of the above.I think somebody just turned all the pieces of the puzzle upsidedown.Makes it a lot harder to put together.I wonder why the truck ran a little rough for months but never got any worse,you would think (starving for fuel?) you would notice a continual decline in performance,but none was observed before and no change after filter change except for smooth idle
 

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Isn't Standyne a demusifier?? Got that free water hanging around??
 

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Yah your right but I don't know if that is the reason for the rust or if it's unrelated.Might have been rusty before it was installed.Even if you used a emulsifier and got a glug of water wouldn't it cause the same problem?
 

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Guess it would but so would a constant small quanity of loose water. I'm in the lock it up school and use the stuff Kennedy sells. George from AV says lock it up and he runs the fuel tests, thats good enough for me.





Also it seems that with loose water have the possibilty of causing rust it makes it easy for GM to deny claims??
 

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I'm bringing this back to the top, as I had both a rough idle, and I also experienced a louder than normal detonation sound under acceleration onto freeways. I figured it was the winter blend of fuel. I was wrong though...for me it was the Total Power additive. I quit using it, and my engine runs smooth and quiet like it used to. I'm not saying this is everyone’s problem..just posting what happened to me. I had started using Total Power this past fall, right around the time the winter blend started. I mixed at the middle ration of 1.5:1. I know a lot of you are using Total Power, and mine may be just an isolated incident. Possibly the Total Power does not happen to work well the additives in the local fuel that I use.

Either way, for those having a rough idle, it may be worth backing off on Total Power (if you are using it) to see if it helps.
 

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I am briniging this back up because I have an answer to the lift pump question and it's effect on the rough idle.


First, some background:


I have an '02 that had a slight lopey idle--only when warming up--and had it reflashed about a year ago. They also told me I had the updated regulator on my truck. The lope pretty much went away and I didn't really notice it again until I had run the Mega pre-OEM for a few months. I disconnected the Meag and the lope went away. While messing around with the disconnected and reconnecting the Mega I introduced air into the system and got a significant lope. I finally installed a lift pump last weekend, and I have had no lope at all. As such, I think my lopey idle when warming up was caused by air.


However, a couple weeks ago I started noticing a bit more of the rough idle at idle when fully warmed up. I know it has always done this, but I have really been paying attention to the idle lately. I talked to JK, and he said sometimes the trucks seesm to do this. He thought it was an injector sometimes getting a bit out of balance or something like that.


Anyway, installing the lift pump did not affect the rough idle at all.


Blaine
 

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When did the updated regulator start going on? Is it all 02's or does it start after some build date? My build was 9/01
 

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Mine was built in Mar of 02 and they told me I had the updated regulator. However, I would also like further confirmation.
 
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