New Truck, Strange Noise

Fishman · July 28, 2005

Took advantage of the employee pricing and upgraded from a Toyota Tundra to a 05' Chevy Duramax Diesel. Very stoked to say the least. I've noticed a strange noise and wanted to see if it's a normal sound in these engines. For some reason I don't remember hearing it when I was test driving the truck. It’s a ticking sound, almost like an old typewriter and it sounds like it's coming from the turbo area. It's not really loud and sounds like it's being generated by air. Exhaust leak?? It's more prominent on the drivers side and only occurs when accelerating or driving at high speeds. It goes away when I take my foot off the gas then comes back when I start accelerating. I had the truck in higher elevation (6000ft) over the weekend and the noise seemed to go away. Not sure why elevation would have anything to do with it. Has anyone else complained of this? The truck only has 2,500 miles on it. I haven’t changed the oil or filter yet.

GM-Tech · July 29, 2005

Could this be what you're hearing?

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Duramax Diesel Pilot to Main Injection Fuel Knock Noise - keywords 6.6 6.6L accelerate engine injector LB7 LLY RPM transition #PIP3422 - (May 10, 2005)

2001-2005 Chevrolet Silverado, Kodiak

2001-2005 GMC Sierra, Topkick

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.

Condition/Concern:

The customer concern may be a fuel knock type noise heard at 2500 to 2600 RPM, or when the vehicle is accelerated with a throttle angle above 80%.

Recommendation/Instructions:

The following is an explanation of the fuel knock noise. The Duramax Diesel has what is referred to as pilot fuel injection at lower engine speeds. Pilot fuel injection is defined as a preinjection of a small quantity of fuel, five to twenty crankshaft degrees, before the main fuel injection. This preinjection softens the main injection pressure rise. When the main injection is softened, normal diesel engine combustion noises are less noticeable. At engine speeds above 2600 RPM and a fuel quantity supply greater than 35 cubic millimeters, it is necessary to eliminate pilot injection to meet emission requirements. When driving at or above this engine RPM range, main injection combustion noise may be noticeable. It is normal and not harmful to the engine. When traveling in fifth gear the pilot injection to main injection transition is typically in the 136 kilometers per hour, or 85 miles per hour range. However, it may also be heard under heavy acceleration with throttle angle at or above 80%, when pulling loads up a hill, and during shifts at or above 2600 RPM. Customers that utilize the fifth gear inhibit switch may encounter the pilot injection to main injection transition noise at speeds around 107 kilometers per hour, or 67 miles per hour.

This sound is considered normal and no repairs should be attempted.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

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Fishman · July 29, 2005

Sounds like my problem although my ticking noise usually starts at or above 2,000RPM's. It's most noticable at the higher end of the low gears and in 5th gear. Is it normal to have it shut off at only 2,000RPM's?