K 3500 Truck 4WD V8-5.7L VIN R (1998)
Vacuum Check Valve: All Technical Service Bulletins
Engine - Ticking Noises
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 00-06-04-045
Date: November, 2000
Subject:
Engine "Ticking" Sound (Install Baffles Into A.I.R. Hoses)
Models:
1998-99 Chevrolet and GMC C/K, G and P Models
with 5.7 L V8 Engine (VIN R - RPO L31) and California LEV Emissions (RPO K18)
Condition
Some customers may comment about a "ticking" sound coming from the engine compartment while the vehicle is being driven. This noise may be
described as similar to valve train noise or detonation, and most noticeable when the engine is completely warmed up (hot) and driven under load (2nd
gear, 30-40 percent TPS, 1800-2500 RPM).
Cause
The noise may be due to an exhaust pressure wave that is migrating past the secondary A.I.R. check valves into the hose plumbing. The pressure wave
produces an objectionable noise similar to valve train noise or detonation. The noise migration is due to system pressure imbalances and is not an
indication of a component part malfunction such as faulty check valves.
1.
Perform strategy-based diagnostics to determine the source of the engine noise. For evaluation purposes. disconnect the A.I.R. crossover tube (3)
and cap off the check valve outlet nipples (1 and 6). If this is the condition responsible for the customer concern, the source of the noise has now
been eliminated and can be confirmed with a test drive.
2.
Procure three baffles, P/N 12562714.
3.
Remove the A.I.R. hose and clamp (2) from the right sloe of check valve (1).
