Lly duramax fuel knock??

Aaron Owner/Technician Holland, Michigan Posted   Latest  
Question
Driveability
2005 GMC Sierra 2500 HD 6.6L (2 LLY) 5-spd (1000)

I’m new to diesels and this is a project truck I did a motor in. I’ve checked the balance rates at idle and they are all well within spec. under a hard accel i get a knock drivers bank somewhere. drive it easy and it’s fine. I’m assuming that this is a fuel knock. I would like to learn how to diagnose this concern correctly. Anyone have any input?

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Adam Owner/Technician
Edmonton, Alberta
Adam Default
 

If your scan tool allows you to disable injectors while driving it'll narrow it down to individual cylinder

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Glen Owner/Technician
Arthur, Illinois
Glen Default
   

Did you program the IQA rates? Sorry see info from Martin below

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Aaron Owner/Technician
Holland, Michigan
Aaron Default
   

The original injectors are still in it. But im sure they didn't go back in to there same location. Maybe an issue you think?

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi Glen. He is working on a 2005 LLY which didn't have IQA programming. IQA programming arrived for 2006 with the LBZ.

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Glen Owner/Technician
Arthur, Illinois
Glen Default
 

Martin, Thanks That would explain why I couldn't find it in SI :|

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

It's east to forget Glen!

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Herminio Mobile Technician
Fontana, California
Herminio Default
 

Check your rubber fuel line at the fuel filter housing, one goes in from the tank and the other is out to the pump, when they are old they collapse under hard acceleration and starve the engine for fuel, these truck don't have a electric lift pump in the tank the injection pump on the engine does all the work.

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Joel Diagnostician
Soquel, California
Joel Default
 

I agree I have seen that condition several times

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Aaron Owner/Technician
Holland, Michigan
Aaron Default
 

This actually had a FASS lift pump installed from previous owner. I will check all my rubber lines anyway though. thanks

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Aaron Owner/Technician
Holland, Michigan
Aaron Update
 

Also my desired and actual pressures are very close to each other

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Rodney Mobile Technician
Monroe Township, New Jersey
Rodney Default
 

my 06 does the same thing apparently its normal on some models to sound like a type writer. I went threw everything on my truck even had a second opinion. # …P: Information on Diesel Engine Ticking Noise - (Dec 21, 2015) Subject: Information on Diesel Engine Ticking Noise Models: … Chevrolet Silverado … Chevrolet Kodiak C4500/C5500 Series … Chevrolet Express…

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Aaron Owner/Technician
Holland, Michigan
Aaron Default
 

Would you compare your knock as loud as a rod knock in a gasser? I did see that bulletin but I just cant believe that my knock would be acceptable. Obviously you thought the same thing having got a 2nd opinion.

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Rodney Mobile Technician
Monroe Township, New Jersey
Rodney Default
 

it is loud . went as far as checking valve lash , injector harness, injectors. strapped a fuel psi gauge to the wipers . no noise in park or neutral taking it to 2500 rpm it soinds like a bad lifter to a wrist pin only under load more load more noise put 60,000 miles on it since I got it its at 127,000 on it now

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Bill Technician
Rosetown, Saskatchewan
Bill Default
   

Depending on your tooling... If you are scan tool only, then tilt down the passenger mirror to see the tailpipe or bring a passenger and observe for smoke during the knock. Do a driving above 1500 cylinder power balance test during the knock to determine the offending injector. If noise and smoke goes away you're done as far as I am concerned. You could scope your fuel pressure sensor for a…

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Matt Educator
North Canton, Ohio
Matt Default
 

Can you get it to quiet down by commanding lower fuel pressure? If it does I would start thinking fuel pressure sensor or circuit. If the ECM thinks the pressure is lower than it actually is, it will command high pressure and possibly get a fuel knock with it. Also check for an aftermarket calibration. Look at the calibration numbers on the scan tool and compare to factory number.

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

All excellent replies. I'm curious if it has an aftermarket tune that is corrupted or just junk injector timing in the tune??

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Rodney Mobile Technician
Monroe Township, New Jersey
Rodney Default
 

mine has stock tune and its loud. even used the scan tool to drop a cylinder at a time and just a slight decrease. note snap on solus is slow as snail to do this constant speed at 1500 rpm I'm sending my pcm out to have a lbz tune stock on my 06 lly . I hate to say it but this one has kicked my butt

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Again just thinking out loud. Is the pump timing off a little causing this noise??

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Rodney Mobile Technician
Monroe Township, New Jersey
Rodney Default
 

On my truck timing is good.

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Aaron Owner/Technician
Holland, Michigan
Aaron Resolution
 

Well wish I had a better responce but after driving it easy a couple hundred Miles and some cetane additive the knock is gone. If it comes back I’ll report any other info but pretty un eventful diag so far

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Matt Educator
North Canton, Ohio
Matt Default
 

Sometimes we forget to look at the obvious. Fuel quality is always the first thing we should consider and I totally forgot about that for your knock issue. Good catch and hope it fixed your problem.

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