02 LB7 White smoke and a knock... ??

[duaner]

I picked up a mint 2002 4 door dually with an lb7 duramax/allison combo and drove it home to PA from Phoenix 2 weeks ago. Truck has california emissions... yuck.

Ok, so when I picked the truck up I noticed that it has a strange knock only under acceleration. I have been reading about "pilot injection" and was hoping that was what I was hearing... but it kept getting louder and louder... then a bit quieter, then louder... etc etc... then last night on my way home on the interstate the sound went away ALTOGETHER... it was so quiet it sounded like a different truck. I thought maybe there was just some schmegma stuck in an injector and it finally cleared out. By the time I got home it was hammering pretty good again. WTH? The thing sounds like a cummins for crying out loud. The truck smokes a little bit at idle... whitish grey. If you let it idle for say 5 minutes or so and then flog the throttle you get a decent sized whitish-gray puff of smoke all at once. Truck seems to run very good with plenty of power... No SES light... I don't believe there is a tune in it.

I have been running lucas in the fuel for about 2800 miles... I changed the fuel filter as soon as I got home... and the oil doesn't appear to be "growing" in the crankcase.

I took it to my local dealer to have them check the injectors cause they are still under warranty... they said the injectors looked good on the computer but that I had a bad MAF and EGR... (p0404 &p0101) and that was what was causing all the noise. They said the sensors were screwing up the timing and fuel mixtures and causing the abnormal sound. They also said the fuel system was only running at 50% because the fuel filter was dirty... that was after I just put a brand new one in. Could there be something other than the fuel filter that is causeing the flow to be decreased?

I didn't believe anything they said, so I took the truck to my mechanic and he cleaned the MAF and reset the codes. MAF is fine now... EGR is still stuck open. Engine still knocks. I put a blocking plate in the egr and now have a p0401 and a p2141. All egr stuff. When I get the new ecm with the egr deleted those should go away... but the engine still knocks.

ANY IDEAS? Is it possible that all the noise is from the egr being defunct? or is that just dealership BS? I still think I have a bad injector somewhere... but the truck starts fine... and runs with good power. I don't know what to do at this point.

thanks

Duane

[TYREBOYZ_DEMAXIN]

it could be the injector harness going bad but IMO it sounds like an injector going bad.not all LB7's with bad injectors start hard or have reduced power but most of them have those symptons some just smoke and sound rough under a hard throttle..take it to another dealer and have them check the injectors to be sure.

[duaner]

Thanks so much for the reply.

I am starting to get stressed here. I don't even know what an injector harness is... but it sounds expensive?

The truck seems to run best under full throttle. The knocking or tapping sound seems to go away completely when the pedal is to the floor.

I noticed tonight that it seems to be idling a little rougher than it did before. Shaking just a tad. The tapping sound is more pronounced now just cruising down the highway too. I noticed also that it changes in pitch a little when you go on and off the throttle while cruising. Kind of like flicking your cheek with your finger and changing how far open you make your mouth... if that makes sense.

Any chance at all that this has something to do with the EGR? I mean, I don't see how... and I don't trust what the dealership told me... but I just want to make sure.

Man, this bites. I really need this truck to be reliable... and If it's the injectors going south I would really like them to go before november when the warranty is up. I can't afford that kind of repair bill any time soon.

I appreciate any input that is offered.
so I can be this guy---->>>

Thanks again,
Duane

[TYREBOYZ_DEMAXIN]

i would highly recommend taking it to another dealer and getting a second opinion on the matter..all the symptons suggest Injectors or the Injector Control Harness and yes those are kinda expensive.


i have just heard of this recently but you may want to check to make sure you don't have algae growing in the tank and that would realy hurt fuel flow and clog filters.

not sure what else it could be.

[duaner]

can poor fuel flow cause a tapping or knock like what I am hearing? I know it does in my little kubota diesel tractor... I once thought my tractor had a rod bearing going bad... i changed the fuel filter and voila... quieted right down. Not sure if the same goes for a duramax.

thanks,
-duane

[gr8shot]

I agree that the algae could be a cause for the fuel system not running at capacity. Did it sit for a long time before you got it? that's how it can start to grow in the tank. Might try some biocide in the tank. i'm not real familiar with how it works, but the bottle ought to tell you all you need to know.

[TYREBOYZ_DEMAXIN]

yes if the engine is not getting enough fuel it will make a knocking sound called retarded timing,perty much to much timing and not enough fuel to go with it almost never happens in stock form but if the fuel system is not flowing right it could cause something like that.

[duaner]

OK... the algae thing is definitely something to look into here. The truck sat for a little over 3 months before I bought it.

My mechanic did another computer scan yesterday. He said all the return rates looked good on the injectors. He also said that fuel system pressure and flow looked pretty good, and that he wasn't sure why the dealer thought that was out of whack. He thought that sound was kind of hollow... almost like a lifter collapsed or something, but we thought that a collapsed lifter would also make noise at an idle, not just under accelleration... and I don't know how a sloppy lifter would make the little bit of white smoke I am seeing either. Again, my mechanic is really good, but he doesn't have a ton of experience with the duramax's, so he's really not sure what to think.

Is it possible that there is some algae crud growing somewhere on the engine side of the filter causing flow to be restricted to just a portion of the fuel system? Maybe just one injector? Enough maybe to cause some injector noise but not enough to throw a flashing ses light?

Oh yeah... he got out his "car doctor stethoscope" and listened to each injector individually as I power braked the engine to put it under just enough load to generate the tapping/knocking. He said the injectors all sounded the same... and that he couldn't hear anything right under the valve covers that would suggest a rocker arm either... we just don't know where the sound is coming from. I would like to say it's just a normal sound, but even the tech at the dealer said it wasn't right... of course, they tried to hose me on the egr stuff too sooooo....... who knows.

thanks for your patience here on the forum trying to figure out a noise for me that you can't even hear. I know it's a long shot, but I am learning alot about this engine.

thanks again
-duane

[TurboDog]

Duane,

I bought a used '01 a couple years back and went through almost the exact same head scratchin' & worring about a mysterious knocking noise, sounds like similar to what you are hearing. I had the same whitish smoke puff when I stomp on it, noise louder then quiet for no reason. It drove me crazy. I tried fuel additives, changed filters, no luck. This one had injectors replaced in 2005, so they were only a year or so old, but it sounded like something was bad wrong.

Then about 35,000 miles later I did loose an injector & there was no mistaking it. While it was torn down I had the mechanic do a compression test on all eight cyliders- which were all fine. So I now know that the knocking was not in the motor.

Anyway, the new injector went in, they checked the balance & flow for all of them, everything is in spec. On my way home from the shop with my new injector - yup, you guessed it, there is a knocking sound.

So, my advice is don't stress yourself out worrying about the noise. You've checked the things that are reasonable suspects and they are fine. GM won't do your injectors without the proper codes turning up, but I would be curious to know if you still have your stock set in there or not?

[duaner]

Thanks for the post Turbodog... I actually feel a little better after hearing from someone with the exact same experiences as I am having. To be honest with you, my mechanic was kind of thinking that I shouldn't worry about it either... but neither of us have a ton of experience with diesels so we didn't want to let it go until we got some more information from some people a little more informed or experienced than us.

He checked the software version on his computer and he said it looked like a GM number. Now, I don't know if there's a tune in the thing if it will show a different number or not. Does anyone know of a way to test for sure if the truck has a tune? My mechanic said the truck runs pretty damn good for being stock, but since he hasn't been in many duramax's... well, he's not sure about that either. There is never any black smoke whatsoever. I know it runs way way better than my brothers 01 dodge with a 50hp tune in it... although his truck has a stick shift.

My mechanic also said that the little bit of white smoke I was seeing at an idle doesn't seem like an amount to worry about... that with a 4" exhaust with basically no muffler and no catalytic converter it's possible that's just how it's going t be. As ffar as puffing a decent cloud after it has idled for a few minutes... I dunno... that seems strange.


Well, I am not ready to post the little "gear jammin" guy yet... not until after I get a good diesel mechanic to take a listen anyways... but I am feeling better.


At any rate,
thanks again, and feel free to chime in with any input you guys might have.
-duane