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We got an 05 K2500 with an LLY Duramax diesel engine that has a knocking noise that is in the top end. Seems to be an injector but we took the injectors out and had them tested with no issues. Machine shop reports no known lifter, rocker or cam issues that he knows of. This noise is there all the time except when the ignition key is turned off and the engine coasts to a stop, then the noise is not present. Truck has 178,000 miles on. Is there any way we can isolate the lifter or injector? Or is there a possibility that it is something else?

does it get louder, faster, higher with increased rpms? or does it stay the same in park a constant tone/knock/tap?

It is constant with engine speed. Does not change intensity or sound. Seems connected to engine rpm. Our diagnosis is leading us to a camshaft issue.

I am just wondering if it is something external making the noise when running. like maybe a fanblade, shroud or something flapping while the air is being pushed around. I know i'm out side the box on this one but........

Will your scanner do a cylinder cutout or contribution test ? That should narrow it down for you, and you can remove a glow plug for a leak down and compression test . These injectors don't like dirty fuel or dirty fuel filters. If the fuel drips off the end of the injector instead of atomizing as it should ti will knock or even hammer. Just a shot in the dark!!

You need to look at a few things with your scan tool. First look at the injector balance rates. Some should have a positive or a negative value. Zero is perfect. Usually the injector with the problems will be pretty far out of whack with the others. You can ramp up the fuel pressure in functional tests to help a bad one show up better. Are you getting an injector circuit code? LLY's are really bad about losing a good connection at the injector plug. Take a sharp, thin awl and poke thru the insulator into the terminal to tighten it up. Most of the time this happens to cylinder 2 and 7. Look at actual and desired fuel pressure and see if they are pretty close to each other. Look at fpr duty cycle. If it's high, prolly have abad injector or possibly a leaky relief valve. Most of the time thaqt just causes low power or limp mode though. I'm betting it's a bad injector. Might try unplugging one injector at a time or a infrared thermometer on the manifolds to isolate the problem. They are about $425 each, so you need to be sure.

Oh, and balance rates all go to zero if you rev up the engine. Might freak you out if you didn't know. I would bet that it is not a mechanical engine problem. A fuel problem on these can hammer pretty good sometimes.

200k injector warranty

Not on an LLY. LB7 ('01-'04) only.

Am I understanding right that in 05 you would lean towards a bad injector as opposed to a mechanical issue? Wouldn't a malfunctioning injector tend to create somewhat of a miss?

protraxrptr17 wrote:Not on an LLY. LB7 ('01-'04) only.

Good call

Tim Martin wrote:Am I understanding right that in 05 you would lean towards a bad injector as opposed to a mechanical issue? Wouldn't a malfunctioning injector tend to create somewhat of a miss?

Not always. He said himself that the noise goes away when you take the fuel away. Of course that could happen with a mechanical problem too, but I have seen this many times before. It's called fuel knock.

just going wayyyyy out here on a limb. i've seen really strange noises resulting from a cracked flywheel.

Ok guys! We began doing exploratory surgery on this engine and found one piston that has a broken piston where the wrist pin goes through it. Never saw something like that before. But there is where the noise was coming from. Very strange. So now we know what to do. Thanks for all yer help.

somebody's using either or some water got in there. see if the piston has a crater like divot in it when you get it out. I'd also see if the rod is tweaked just a bit.

steve! ether? ya gotta be kiddin me. you know that ain't nobody uses ether on their trucks. but that is one of the first things i thought of although owner says he doesn't use it.

Post a pic. Would like to have this one for my notes. The newer engines (LBZ's) supposedly have weak pistons, but the LLY's are supposed to be pretty strong. I changed a water pump and fixed the "pump rubbed" transfer case in a 2500 LLY that was knocking a few months back. Balance rates were all good. The owner wasn't concerned and said it had been doing it for quite some time. Told me he just wanted the water leak and tranfer case leak fixed.

I missed that one bad We have a guy that gets on the local morning news show and diagnoses cars over the phone. Guess I'm not ready to take his job just yet. He owns a shop in the same city as the TV station. I often wonder how they work out the $$ on that deal.

I often wonder how they work out the $$ on that deal.[/quote]
yea. aint? Oh well.