Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to all brands, models and engines, 2000 - 2019.

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  All All 2000 - 2019 All All All All

• The tip is for cases where cylinder bore damage, scoring or out of round is suspected as the cause of engine 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

• Dirt intrusion: if the air filtering system has been compromised the engine wears out very quickly; grit is found in the intake runners and the bores look lightly sand blasted.

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  3. Dirt intrusion- If the filtering system has been compromised the engine will wear out very quickly. You will find grit in the intake Runners and the cylinder bores will look lightly sand blasted.

• Catalytic converter failure: if the converter brick is broken, its dust can be drawn back into the engine, and the bores look sand blasted.

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  4. 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.

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   The peak to valley spec for crosshatch is .65-2.8 microns.

2. Cylinder damage or scoring: the cylinder walls have grooves deep enough to catch with a fingernail.

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   1. 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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   2. 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 back cylinders go first if caught early; otherwise there is no crosshatch left and the engine needs to 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 an issue with cylinders being machined out of round for 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.

• A cylinder suspected of being oversize can only be confirmed by checking with an air gauge at the engine plant.

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  Even if a cylinder is suspected of being oversize we can only confirm that by checking with an air gauge at the engine plant.