Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 2014 and prior GM passenger cars and trucks.

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  2014 and Prior GM Passenger Cars and Trucks

• The engine block is suspected of cylinder bore damage, scoring or out-of-round as the cause of oil consumption, misfire, cylinder leakage or blow-by.

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  Suspecting an engine block of possible cylinder bore damage, scoring or out of round as the possible cause of engine oil consumption, misfire, cylinder leakage or blow by.

Possible causes

• With dirt intrusion there is grit in the intake runners and the bores look lightly sand blasted, with faint crosshatch that has lost its sharpness.

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  You will find grit in the intake runners and the cylinder bores will look lightly sand blasted. The crosshatch will be faint and there will not be sharpness.

• If a catalytic converter fails and its brick breaks, the dust can be drawn back into the engine, and the bores look sand blasted.

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  Catalytic Converter failure - If a converter fails and the brick is broken, the dust can be drawn back into the engine. A block showing this type of failure will have bores that look to be sand blasted.

Steps to confirm (in the document’s order)

1. The peak-to-valley specification for the crosshatch is .65-2.8 microns; with any deviation the crosshatch will be gone.

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   The peak to valley spec for crosshatch is .65-2.8 microns. Any deviation and the crosshatch will be gone.

2. Cylinder damage or scoring shows as grooves in the cylinder wall deep enough to catch a fingernail.

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   Cylinder damage or scoring- the cylinder walls will contain grooves deep enough to catch with a finger nail.

3. An out-of-round bore has areas where the crosshatch is missing or worn in different sections of the bore.

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   An out of round cylinder bore - will contain areas where the cross hatch is missing or worn from different section of the cylinder bore.

4. If crosshatch is present all the way around the bore from top to bottom, the bore is not out of round.

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   If there is crosshatch all the way around the bore from top to bottom the cylinder bore is not out of round.

Repair

• With converter dust the rear cylinders go first if caught early; otherwise there is no crosshatch left and the engine must be replaced.

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  Back cylinders go first if caught early. Otherwise there will be no crosshatch and the engine will need to be replaced.

Caution

• GM has not had a problem with cylinders machined out of round on any engine family in recent history.

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  Note: GM has not had an issue with cylinders being machined out of round for any engine family in recent history.