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Cause tapping noise ar 2500 rpm and up on a 06 chevy 6.6 diesel?

Customer Question
what could cause tapping noise...
what could cause tapping noise ar 2500 rpm and up on a 06
chevy 6.6 diesel?
Submitted: 8 years ago.Category: Chevy
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Answered in 3 hours by:
6/27/2010
Chevy Mechanic: Hal, Chevy Master Tech replied 8 years ago
Hal
Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1,032
Experience: ASE and Chevy Master , 31yr Dealership exp,
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Hi My name isXXXXX to just answer.

 

A slight knocking noise will occur at 2500 rpm due to the pilot pulse for the injectors is eliminated above that rpm. The pilot pules is a little shot of fuel just before the main shot of fuel is injected.

This allows the fuel to start burning , and helps continue the process when the main shot of fuel is injected. This is one of the reasons the duramax engine is so quiet.

 

This is a normal condition.

 

An abnormal knock noise would be very loud, followed by black smoke out the tail pipe.

This would also be occurring at slower rpm speeds.( generally starts around 1800 rpm)

 

 

Fuel System

The fuel system is of a direct injection fuel rail design. A high pressure pump mounted within the valley is gear driven directly from the camshaft. This pump provides a continuous and constant high pressure fuel supply to the fuel rails. The electronically controlled fuel injectors receive their fuel supply from these fuel rails. The fuel injection control utilizes a pilot injection method to reduce the combustion noise that is common in traditional diesel engines. The pilot injection method reduces noise by supplying a small amount of fuel to the cylinder just before the normal combustion timing.

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Customer reply replied 8 years ago

I understand about the common rail injection process, what concerns me is about 2300 to 2500 the tapping noise grow louder as rpms go higher, sounds like a gas engine knocking under hard exceleration with too much timing, could it be injection timing map not in sink with the fuel map in the program. There isn't heavy black smoke.

Chevy Mechanic: Hal, Chevy Master Tech replied 8 years ago

 

Timing is controlled by the ECM. If there is not a SES lamp or signs of smoke out tail pipe( black smoke /over fueling) Indication of mileage loss. It most likely a normal condition. If you feel it is abnormal , then that can be tested. The engine can be operated until the knock occurs. Then the cylinder can be canceled.if there is a noticeable change in noise level, that injector should be replaced. Unless someone has changed the programing with a power up device, the fuel mapping for the vehicle should work.

It may be possible, not to be able to notice a smoke condition out of the tail pipe while driving. It usually takes someone following to notice a smoke condition under hard acceleration.

There has been some instances where a ceramic ball fractures in the pump and sends debris through the fuel system and causing fuel system components to stick.

This document is bulletin 08-06-04-029c, It does not list a noise , as one of the symptoms. Low fuel pressure P0087 DTC's are usually set.

 

There is another bulletin PIP 3491 C It state fuel system injector knock, excessive smoke, Insect for fuel system rust contamination/water in fuel. If none is found , and balance rates are high. recommend to use a diesel fuel additive like RACOR power shot, or STANADYNE fuel additives that are alcohol free.

 

I have not seen the LBZ programing cause a fuel knock. There have been several EGR issues , that a program has taken care of.

Most cases of fuel knock have been resolved by fuel additive or replacing a single injector. Fuel quality is allot of the problem. Quality is not consistent from station to station.There are several articles referring to this on stanadyne,com websight, and GMs endorsement of using the stanadyne additive, along with several other manufacturers.

 

 

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.

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