LBZ Running sort of rough around 1400-1700 rpm

[Cloudy]

Hi, I have a 2006 LBZ bone stock with 170k miles that I bought not long ago. When driving around 1400-1700 rpm, the engine sounds really "choppy" almost, much moreso than my previous LBZ. It reminds me of how an old single shot injector 7.3L PS sounds when accelerating. Almost like an injector isn't firing exactly correctly or there's a slight miss. I know it's hard to know the issue from someone just describing it, so I'll try to get a video here pretty soon.

I checked the balance rates and all the injectors were +/- 2, so in spec. No haze at idle, no raw diesel smell, smokes a little more than what I'd expect when you really lug/get on it for a stock engine, but nothing excessive, engine idles fine (but sometimes sounds a little more tappy than my other LBZ as well). Plenty of power still. Fuel filter is pretty fresh, oil is fine, truck came with service records when I bought it and did mostly highway driving and is well serviced. Fuel economy is pretty normal. Because of all of this, doesn't really seem to me like the injectors are going bad, and might be something else.

Mainly just wondering if anyone has ever dealt with something like this. The truck still runs and drives pretty much fine other than just being somewhat annoying sounding when driving around 35 mph in town. Had a buddy who was saying maybe your crankshaft is about to go which got me sort of paranoid.

 

[DAVe3283]

I'm not super familiar with the exact quirks of the LBZ, but I can put your fears to rest (then instill new ones) about the crankshaft. Crankshafts don't have any warning before they break. They are perfect, until they are in 2 pieces. While the actual break might take some time to happen, until it separates, everything works like normal, since it is still all connected. So don't worry about the crank being about to break. Well, not anymore than any other Duramax.

But seriously, stock trucks almost never break cranks. It has happened, but most broken cranks occur on 800+ HP motors. Though often when just cruising the highway, oddly enough.

 

[IOWA LLY]

Sounds like it needs injectors.


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[Cloudy]

https://youtu.be/H9o9orryE3Q

Here's a video where I tried to capture it. Didn't really come out well but near the end of the vid you can hear it the best.

Also, something else to note is that it's much more noticable when the engine is at operating temp rather than when it's cold. I don't notice it much until it's at operating temp.

 

[Blackmax123]

I couldn't hear anything in the video except maybe your keys jingling.

 

[Cloudy]

A guy on FB posted a video that pretty much showcased way better the sound it's making, but I think the post was deleted cause I can't find it now.

Anyway, more concerning news: today I was driving up a fairly steep grade hill, unloaded, but accelerating. Heard a loud "pop" sound, and at first thought it was rock that that got picked up and shot out of my tires, but then I looked in my passenger side mirror and there was a big cloud of grey smoke that had come up. Thought "holy f***" just blew my engine" but it kept driving completely fine after, full power and no smoke. Drove fine the rest of the time until it did it again later than night when I was accelerating on a left turn, once again puff of grey smoke but that was all.

I know diesels don't backfire, but it pretty much reminded me exactly of a backfire. Never heard of this happening on a Duramax....

 

[DAVe3283]

It could be an injector is occasionally hanging open. If it hangs open after one firing event through to the end of the next, it would dump an extra 2 engine revolutions worth of fuel, most of which wouldn't burn because valves would be open. That could cause a bad sound and grey smoke.

If that injector is also slow to close most times, it would throw the pilot injection event way out, which can change engine sound.

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[Cloudy]

It could be an injector is occasionally hanging open. If it hangs open after one firing event through to the end of the next, it would dump an extra 2 engine revolutions worth of fuel, most of which wouldn't burn because valves would be open. That could cause a bad sound and grey smoke.

If that injector is also slow to close most times, it would throw the pilot injection event way out, which can change engine sound.

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Yep sounds about correct. An injector (or a couple) definitely have failed. I was sitting in traffic yesterday, when suddenly I noticed the truck was shaking. Turned the music down and it was knocking bad. No blow-by though.

To the shop it goes....

 

[Cloudy]

https://youtu.be/_ubpeLw8Wesi

Nothing better than the sound of your truck running like s*** on a Saturday morning.

 

[Cloudy]

Well, just one more update in case anyone's curious or if there's someone having similar problems to me later on. Just got a call from the mechanic, yep injector #6 failed. Three other injectors have poor flow rates but once #6 is replaced it's possible that they'll be more in spec.

Thankfully I paid LB7 money for this truck and not LBZ money, otherwise I'd be pretty choked

 

[DAVe3283]

The injectors wear out on all year models, it was just the LB7 is somewhat more complicated to change injectors, and early ones had various issues. At least with the LBZ it is practical to replace just one injector.

Hopefully you'll be good to go now, thanks for reporting back!

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[Cloudy]

Well, the shop I took it to also screwed me I'm pretty sure on the pricing of the injector. 3.3 hours of labour to replace which is fine and I'm happy with, but the part cost on the injector was $917.38. WTF? This was for a Bosch OEM injector. Beyond frustrating honestly. Looking online, Lincoln Diesel sells OEM Bosch injectors for $340 USD. I'm in Canada, so that translates to roughly $440 CAD. I guess they ordered the injector through GM and then threw some ridiculous parts mark-up on it. Brutal. Oh well, live you learn I guess. I bet they must charged $11k to replace all 8 then.

Talked to the mechanic as well, said injector #8 is actually at around +4 on a return flow test, and that the truck won't be running exactly perfect. Recommended running some injector cleaner through it and that should get some extra life out of it. Two other injectors were also at around +/-3 but fell below 3 after being replaced.

 

[DAVe3283]

Yeah, you got a bit hosed on that injector. The GM dealer might have charged the mechanic that much, though, so hard to say who hosed you. Either way, that sucks.

Well, now you know for next time, get the injectors from Lincoln Diesel or similar reputable shop, and save some cash.

Hope the truck runs better now.

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