Manufacturer communication — 2006 GMC YUKON DENALI XL

• The model list names 1999-2013 GMC Savana, Sierra and Yukon with a V8 engine.

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  1999-2013 GMC Savana, Sierra, Yukon 2003-2010 Hummer H2 2008-2010 Hummer H3 2008-2010 Pontiac G8 2005-2006 Pontiac GTO 2005-2008 Pontiac Grand Prix GXP 2005-2009 Saab 97x with a V8 engine

• With the SES light on, a P0300-P0308 DTC is found with misfires counting on a single cylinder that 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); it may be a chirp, squeak, squeal or tick and may increase off idle.

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  If a noise is verified, it will not be eliminated by canceling fuel injectors and the noise will occur at camshaft speed (half of crankshaft speed). The noise may be described as a chirp, squeak, 1 squeal, or tick noise and may increase off of idle.

Possible causes

• When 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 valve side, push rod side and side of each rocker arm; if pressure on the valve side changes the noise, it is most likely a lifter and/or cam lobe concern on that cylinder.

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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. 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.

2. Measure cam lobe lift at the push rod side of the rocker arm and compare with other rockers on the same bank; the misfiring or ticking cylinder should have clearly less lift if a lifter roller and/or cam lobe is worn.

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   Measure the cam lobe lift at the push rod side of the rocker arm. The lift in this location will differ from the SI specification but it should be similar as compared with other rockers on the same bank. The misfiring/ticking cylinder should obviously have less lift than the comparison cylinders if this is the result of a worn lifter roller and/or cam lobe.

3. A good indicator of a sticking valve is 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.

4. For a suspected sticking valve, snap the valve onto its seat and confirm it comes off easily; if force is needed to tap it off the seat, excessive carbon build up exists, which may be repaired by decarboning the engine.

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   If okay, rotate and snap the valve onto the valve seat to make sure that it easily comes off of the seat again. If you have to use force to tap the valve off of the seat, excessive carbon build up exists, which may be repaired by decarboning the engine.

5. The Cylinder Leakage Test outlined in SI should isolate valve leakage by finding excessive leakage past an intake or exhaust valve compared with the others.

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   Typically, the Cylinder Leakage Test outlined in SI should isolate valve leakage by finding excessive leakage past an intake or exhaust valve, as compared with others.

6. A broken valve spring may stay stacked together and be hard to see, so lightly push on different places on the springs with a small hammer handle.

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   Sometimes, the two broken pieces of the spring will remain stacked together so it may be hard to detect when visually inspecting them. As a result, it may help to lightly push on different places on the springs with a small hammer handle.

Repair

• If a worn camshaft lobe or lifter roller is found, replace the camshaft and all lifters per SI, and also replace the plastic lifter guide for the lifter that had the damage.

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  Follow SI procedures to replace the camshaft and all lifters if a worn camshaft lobe or lifter roller is found. Also replace the plastic lifter guide for the lifter that had the damaged cam lobe and/or lifter roller

Caution

• A worn cam lobe is easy to overlook through the lifter bores, and unworn lifter rollers do not mean the related cam lobes are okay; both must be carefully inspected.

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  It is very easy to overlook a damaged cam lobe when inspecting them through the lifter bores and just because the lifter rollers are not worn, does not mean that the related cam lobes are okay. Both pieces need to be carefully inspected.