LB7 lower engine knock

[briencolgan]

Good Morning. I have an LB7 with 305K. It sounded like a "marichi band" according to one friend last fall and was spewing a rooster tail of black smoke before it just quit. I went out a few days ago and it fired up. The whole engine rocks pretty violently at idle. I thought maybe a broken crank but the HB doesn't wobble. I'm thinking its time to pull this thing and rebuild but I was kinda hoping it was something simple like a stuck injector. My scanner isn't reading balance rates so I'm trying to figure that out. But the most telling is a very sycopated firing at idle. and strangly now no black smoke. that might of only been happening when I was driving it.

 

[darkness]

Isn’t reading balance rates as in zeros across the board or can pull them up at all?
And what’s the life of those injectors?

 

[briencolgan]

Yep. All zeros. With two different scanners. A Zurich ZR pro and Autoenginuity. No idea on the injector life. They were in the truck whe I bought it. I’ve replaced one injector so far.

If anybody’s got a guess, I was just hoping someone with more experience with these engines might recognize something. I’m pretty sure it’s time to pull the motor but just looking for little advice before I do.


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[Bdsankey]

I wouldn't rule out an injector. Take your scanner and cancel one injector at a time and see if the smoke goes away etc as well as do a compression test through the glow plug bore. It's way faster than pulling an engine and would at least point you in the proper direction IF the motor does need to come out.

 

[briencolgan]

That’s what it was—thanks. It’s crappy scanners that caused the troubleshooting errors. They don’t reliably shut down injectors. Finally got it to shut down #7. And all the wobble and slap went away.

Well now I know a bad injector makes a hell of a racket. A very well respected mechanic in town took a listen and it fooled him as well. A Bad injector makes a lot of lower engine knock. It sounds really bad like a rod is broke or crank. And the motor really rocks back and forth on its mounts.

I’ll poke around here and see if I can find the place to send them out for rebuild.


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[2004LB7]

Contact Lincoln diesel for injectors

 

[briencolgan]

This has been addressed elsewhere in the forums, but I’ll mention it here. I don’t think My diagnostic issue was the scanners fault.

I read that if balance rates are too far out of spec, the duramax computer will just default to showing zero on the balance rates.

I wish I’d googled “LB7 balance rates zero” long ago. I just made the assumption that the scanner was corrupting the values. I never considered
The computer was actually outputting those values.


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[2004LB7]

This has been addressed elsewhere in the forums, but I’ll mention it here. I don’t think My diagnostic issue was the scanners fault.

I read that if balance rates are too far out of spec, the duramax computer will just default to showing zero on the balance rates.

I wish I’d googled “LB7 balance rates zero” long ago. I just made the assumption that the scanner was corrupting the values. I never considered
The computer was actually outputting those values.


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And if the RPMs are out of spec too far, such as when pressing on the accelerator or when the ecm is having trouble maintaining proper RPM due to the injectors being too far out, tuning issues,, pressure regulator problems, etc