lly valve rattle

[leroy creeper]

hello, first post. cool website.

i have an 04.5 lly 2500hd. i have had a cummins before, so im not new to desiels too much.

from the day i bought this truck, i swear i think the valves rattle. i can hear them always at mid rpm under very light throttle. my father and friends have brought it up without my prompting as well. i have taken it to the dealer twice and even had the service manager ride with me. he says, he hears it too, and thats the way it supposed to sound. i say he's crazy....i've been busting my knuckles on cars my whole life, i im pretty sure i know what a valve rattling sounds like.

but then again, the guy's a gm certified master mechanic, and im not. does anybody else have this problem?

[BMDMAX]

I can't say that I have experienced any valvetrain noise with either of my trucks. The V8 diesels and the injection event in the Duramax sounds quite a bit different from the Cummins that you are used to hearing. I would drive and not worry. ;)

[Mark Rinker]

Welcome a-board!

If you drive with a heavy foot - you may be hearing the sound of a 'de-fueling' rattle, when the Duramax 'pilot injection' that is normally present is withdrawn.

"Diesel engine fuel injection systems that use a common rail system, as the Duramax diesel does, may or may not have what is referred to as pilot fuel injection at the lower engine speeds. Pilot fuel injection is defined as a pre-injection of a small quantity of fuel 5 to 20 crankshaft degrees before the main fuel injection. This pre-injection softens the main injection pressure rise and reduces combustion noise. At engine speeds above 2600 RPM, and a fuel quantity supply greater than 35 cu mm, it is necessary to eliminate pilot injection to meet emission requirements. When driving at or above these speeds, main injection combustion noise may be noticeable. It is normal and not harmful to the engine.
When traveling in 5th gear, the pilot injection to main injection transition is typically in the 136km/h (85 mph) range, however it may also be heard under heavy acceleration and when pulling loads up a hill during shifts at or above 2600 RPM. Customers that install the fifth gear inhibit switch, (ODLO), may encounter the fuel knocking of main fuel injection at speeds around 107 km/h (67 mph) in fourth gear between 2600 and 2700 RPM. This sound is considered normal and is to be expected."


Search this forum for more info and similar questions by other members...

[Kennedy]

I wouldn't get excited about it. Diesels run on "rattle" and if you drive light pedal/light boost you will likley hear more of this. As Mark stated, the pilot injection switching off can also catch some people by surprise.

[leroy creeper]

i do hear it the most when i let out of it and start to just maintain speed. thanks guys. hope that's it!