stock duramax rough idle

[hutch]

Hey guys, I have a bone stock 2004.5 duramax. Sometimes it has a really rough idle. I can only notice it when its in gear and i am at a stop. I can hear the engine "laboring" at one spot and it lunges forward at that exact spot. All i have done to it is exhaust and i dont know what woulkd make it run like this. when im driving along in overdrive and i come to a complete stop slowly, i can hear the engine running rough as the transmission downshifts but you cant notice it untill you have your foot on the brake trying to hold the truck there. Any ideas, thank you

[killerbee]

Did you say you tuned it? If so, it might help to post the tune. I can spot these kinds of things if they are tune related, I have spent a fair amount of time creating these kinds of problems for myself.

What is you idle speed?

[hutch]

i have not tuned it yet, i plan on doing so very soon but i want to make sure there isnt any existing problems before i start doing that. its totall bone stock and i think the factory idle speed is 680? i believe, not 100 % positive. the guy that i bought it from said that an injetor wire chaffed and shorted out and it blew the fuels system fuse? not really sure what he was talking about. im still learning. he said that the wire was not damaged so he put a small peice of electricaal tape around the are that was shorted. i dont know if this would couse a condition like this? thanks,

[killerbee]

oh, ok, yes sounds like the fuel wire harness chaffing.

Yes, 680 is stock idle speed. If you can see the tach needle moving around while stationary, you have a problem.

[hutch]

ok, i can def notice the needle moving and jumping a small amount, at some points it gets reall bad and can really notice it through listening to the exhaust, nevermind it makes the truck want to take off everytime it jumps. what do you think i should do? can i repair the harness or will i have to buy a new one to do it the right way?

[LBZoom]

My dad's truck had the same issue, about 7 months ago and it was a bad injector, so could be the harness damaged or the injector.

[KB3MMX]

Could it be fuel filter pedestal O-rings leaking on the primer pump, etc?
I seen that Nicktane diesel has a rebuild kit for them if you're sucking air,etc..

[FUELPUMP575]

MY 2004.5 has done the same thing a couple times. The first time it started happening, the dealer replaced 1 or 2 injectors, but it continued to ack the same way intermitantly. The dealer then replaced the fuel psi regulator & problem was gone for 2 years & now is starting to slowly reoccur. I suspect it will need to be replaced again.

[roy67ss]

Sounds like the fuel pressure regulator.

[schwoch1]

Sounds like the fuel pressure regulator.

I was going to say the same thing, but I am not sure if the '04.5 had one, not a diesel guy. I just put one in an '03 Duramax yesterday for an idle surge problem and it worked out well, no more surge!!!

Mike