LB7: 2003 LB7 Surging Idle

guyatlantic

New member
Oct 16, 2012
9
0
0
Fairbanks, AK
Hello all,

Ive been trolling the forums for quite a while. This forum is a never ending well of information.
Was hoping yall could help me out a bit. I have a 2003 lb7, bought it about a year ago. Has roughly 210,xxx on it right now.
Over the past few months I've noticed a knock, dont think it is rod related as it only does it under load. Seems to be getting worse.
More recently over the past 2 weeks, I've changed my fuel filter, NAPA Gold to be exact, since I've changed it, it surges at idle. Mainly when cold but off and on throughout the day. When its surging and put it in drive, start driving and let off the throttle it will bog down to about 600 rpms and almost shut off, then pop back to normal surging. The fuel filter doesnt seem to be holding prime.
I just find it weird that the truck was fine before I switched the filter, minus the knock. That it would go from fine to surging with a simple fuel filter switch.
I am wondering if it is sucking air from somewhere, and hoping its not the FPR lol.

Anyways, I have taken some of the measures on here and applied to no avail.
I have ran 2 stroke oil in hopes that if it was the FPR it would smooth it out,and ran a bottle of Diesel Kleen.
Will most likely buy another filter this weekend and try to see if i get lucky.
Also looked at the rubber fuel lines coming from the filter housing they do have small dry rot like cracks in them, will probably replace those as well.

Other than that, does anyone have any other ideas? I apologize for the long drawn out post, but I didnt want to leave out too much detail.
Thanks for any replies.


In addition somethin I forgot to mention, the truck will not rev beyond 2200-2300 rpms while in park as if the high idle was active. It goes above that point while in drive.
 

OregonDMAX

NOT IN OREGON, NO DURAMAX
Apr 28, 2013
3,964
8
38
35
Goodyear, AZ
you could be sucking air somewhere around the filter area, since you just did a filter that would be the best place to start.

get a fuel filter head rebuild kit, its just a couple of o-rings, that has seemed to fix a ton of some people issues. (merchant automotive sells the kit) easiest place to start and a cheap fix if it works.

i may be wrong but that sounds like a safety feature, every duramax i have driven has the idle in park maxed out at 2k
 

02greysixer

Active member
Jun 4, 2011
1,829
7
38
North Central FL
Definitely start by trying to track down any air leaks you may have. But if your truck has never had injectors done I suspect they might be part of your issues too. Especially since you say you have what sounds to me like a fuel knock. If you don't have the means it may be worth taking it to a good dealership or shop and paying the diagnostic fee to let them check out the fuel system.
You should be able to rev the truck higher than 2200 in park. It should go up to the rev limiter which is somewhere around 3300rpm. Only the newer trucks have the safety limiter in park far as I know.

sent from a galaxy far far away
 

DBUSHLB7

Team DMAX
Mar 9, 2012
2,789
0
0
Albuquerque, NM
you could be sucking air somewhere around the filter area, since you just did a filter that would be the best place to start.

get a fuel filter head rebuild kit, its just a couple of o-rings, that has seemed to fix a ton of some people issues. (merchant automotive sells the kit) easiest place to start and a cheap fix if it works.

i may be wrong but that sounds like a safety feature, every duramax i have driven has the idle in park maxed out at 2k


http://www.merchant-automotive.com/completefilterheadrebuildkit.aspx
[YOUTUBE]9boIwwN-AHA[/YOUTUBE]
 

guyatlantic

New member
Oct 16, 2012
9
0
0
Fairbanks, AK
Welp, trying to bring this thread back from the dead.
**Update**** from close to a year ago.

So I ended up rebuilding the fuel filter housing. Surging for the MOST PART went away, but still randomly there.
I see someone mentioned the FPR being a possible culprit. Would that make the fuel knock expalinable? I have no smoke no oil in crankcase. The only reason I mention that is its my way of expressing hope its not injectors lol.
The only new thing as of this year, is it seems to lose some power like "bog down" when i press the pedal heavier than usual.

Any ideas or information would be greatly appreciated!
 

roughneckdan

New member
Dec 9, 2014
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0
0
Hate to say it but might need injectors. I had problems like yours plus more and it all cleared up after injectors. I had opened up both sides twice to change injectors. I never had fuel in the oil but it surged often and had the fuel knock . After i changed all 8, it ran perfect. I have efi live now but i bought it with a slight mileage tune which they turned up the fuel pressure and caused them to wear out faster then normal. But before jumping into injectors, i would try to flush them with the gm upper engine and injector cleaner method. It did make a difference when i did it.