Manufacturer communication — 2006 GMC YUKON DENALI

• Applies to GMC Yukon models, 2002 - 2018, with a V8 engine.

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  Yukon Models 2002 - 2018 All All V8 ALL

• Customers may complain of an SES light, engine misfire, and/or engine noise.

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  Some customers may complain of a SES light, engine misfire, and/or engine noise.

• If the SES light is on, there will be a P0300-P0308 DTC with misfires counting on a single cylinder, which may or may not be felt.

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  If the SES light is on, the technician will find a P0300-P0308 DTC with misfires counting on a single cylinder that may or may not be felt.

• A verified noise is not eliminated by canceling fuel injectors and occurs at camshaft speed (half of crankshaft speed).

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  it will not be eliminated by canceling fuel injectors and the noise will occur at camshaft speed (half of crankshaft speed).

Possible causes

• If SI diagnosis does not isolate the cause, it may be a worn camshaft lobe and/or lifter roller, a sticking valve, valve leakage, a broken valve spring, or a collapsed AFM (Active Fuel Management) lifter.

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  1. Worn camshaft lobe and/or lifter roller 2. A sticking valve 3. Valve leakage 4. A broken valve spring 5. A collapsed AFM (Active Fuel Management) lifter.

Steps to confirm (in the document’s order)

1. During the noise, press with a wooden hammer handle on the rocker arms at the valve side, push rod side, and side of the rocker to find which one is making noise.

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   Use a wooden hammer handle to apply pressure to the following locations of the rocker arms during the noise to determine which one is making noise: valve side, push rod side, and side of the rocker.

2. If pressure on the valve side of the rocker changes the noise, it is most likely a lifter and/or cam lobe concern on that cylinder.

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   If the noise is changed by applying pressure to the valve side of the rocker, this is most likely the result of a lifter and/or cam lobe concern on that cylinder.

3. Measure the cam lobe lift at the push rod side of the rocker arm.

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   Measure the cam lobe lift at the push rod side of the rocker arm.

4. A good indicator of a sticking valve is engine misfires that continue to count on an aggressive deceleration with engine braking.

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   A good indicator of a sticking valve is if engine misfires continue to count on an aggressive deceleration with engine braking.

5. Release the air pressure from the cylinder and work the valve up and down in the guide while turning it 360 degrees; if any binding is felt, a stem to guide clearance concern exists.

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   Release the air pressure from the cylinder and work the valve up and down in the guide while turning the valve 360 degrees. If any binding is felt, a stem to guide clearance concern exists and should be repaired by following SI procedures.

6. Typically, the Cylinder Leakage Test outlined in SI should isolate valve leakage.

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   Typically, the Cylinder Leakage Test outlined in SI should isolate valve leakage

Repair

1. If a worn camshaft lobe or lifter roller is found, follow SI procedures to replace the camshaft and all lifters.

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   Follow SI procedures to replace the camshaft and all lifters if a worn camshaft lobe or lifter roller is found.

2. Also replace the plastic lifter guide for the lifter that had the damaged cam lobe and/or lifter roller.

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   Also replace the plastic lifter guide for the lifter that had the damaged cam lobe and/or lifter roller

3. Refer to the latest version of PIP4753 for decarboning instructions.

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   Refer to the latest version of PIP4753 for decarboning instructions.

4. If a broken valve spring is found, replace the broken valve spring as necessary.

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   If a broken valve spring is found, replace the broken valve spring as necessary.

Caution

• If an AFM lifter concern is suspected, refer to the latest version of PIP4568 for additional information.

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  If either of these AFM lifter concerns is suspected, please refer to the latest version of PIP4568 for additional information.