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Could be TWO things---the one mentioned above, but also this one:
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 02-06-01-038
Date: December, 2002
TECHNICAL
Subject:
Engine Knock or Lifter Noise (Replace 0-Ring)
Models:
2001-2002 Chevrolet Camaro
2001-2003 Chevrolet Corvette
2001-2002 Pontiac Firebird
2002-2003 Cadillac Escalade, Escalade EXT
2000-2003 Chevrolet Suburban, Tahoe
2001-2003 Chevrolet Silverado
2002-2003 Chevrolet Avalanche
2000-2003 GMC Yukon, Yukon XL
2001-2003 GMC Sierra
with 4.8L, 5.3L, 5.7L or 6.0L V8 Engine (VINs V, T, Z, G, S, N, U - RPOs LR4, LM7, L59, LS1, LS6, LQ9, LQ4)
Condition
Some customers may comment on an engine tick noise. The distinguishing characteristic of this condition is that it likely will have been present since new, and is typically noticed within the first 161-322 km (100-200 mi). The noise may often be diagnosed as a collapsed lifter. Additionally, the noise may be present at cold start and appear to diminish and then return as the engine warms to operating temperature. This noise is different from other noises that may begin to occur at 3219-4828 km (2000-3000 mi).
Cause
The 0-ring seal between the oil pump screen and the oil pump may be cut, causing aeration of the oil.
Correction
Inspect the 0-ring seal and replace as necessary. Use the applicable part number listed below. Refer to the Engine Mechanical sub-section of the appropriate Service Manual.
HERE'S THE BULLETIN ON THE CSK
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 01-06-01-028A
Date: March, 2003
INFORMATION
Subject:
Engine Knock on Cold Start
Models:
1999-2002 Chevrolet and GMC C/K Pickup and Utility Models
2002 Cadillac Escalade (2WD)
with 4.8L, 5.3L or 6.0L Engine (VINS V, T, Z, U - RPOs LR4, LM7, L59, LQ4)
This bulletin is being revised to add an additional engine to the models section. Please discard Corporate Bulletin Number 01-06-01-028 (Section 06-Engine).
Some of the above vehicles may exhibit an engine knock noise that begins in the first 19,000-24,000 km (12,000-15,000 mi) of use. The knock noise is most often noticed during initial start-up and typically disappears within the first 5-30 seconds (may last longer in extreme cold temperatures). The noise is usually more noticeable on the initial start-up when the temperature is below 10°C (50°F) and may be more pronounced on the first cold start following a long trip.
This noise may be caused by an interaction between carbon that has formed on the piston, the piston motion and the cylinder wall. GM Powertrain Engineering, and an analysis of engines with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine.
THIS NOISE DOES NOT HAVE ANY EFFECT ON THE LONGEVITY OF ANY OF THE ENGINE COMPONENTS.
Important: At this time, attempts to repair this condition by replacing the engine assembly or pistons are not recommended.
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