By Ed Dorowski, ALLDATA Editor
and Jeff Webster, ALLDATA Technical writer
CONDITION: Some General Motors truck owners may comment on a popping/snapping noise from under the vehicle at idle or immediately after the vehicle is shut off. Some popping/snapping noise from the exhaust system during cool down is a normal condition. The noise may be intermittent depending on the outside temperature and or temperature of the exhaust system at the time of testing.
CAUSE: As the exhaust system warms and cools, the muffler and the muffler heat shield expand and contract at different rates and may cause a popping and/or snapping noise. Some noise from the exhaust system during cool down is a normal condition. The vehicle owner should be made aware that this service procedure is designed to reduce but not eliminate all exhaust system popping and snapping during cool down.
To correct the condition, replace the muffler heat shield following the steps in this Tech Tip.
2002-2006 Cadillac Escalade, Escalade EXT
2003–2006 Cadillac Escalade ESV
2002–2006 Chevrolet Avalanche, Suburban, Tahoe, Silverado, Silverado HD
2007 Chevrolet Silverado Classic, Silverado HD Classic
2002–2006 GMC Sierra, Sierra HD , Yukon, Yukon Denali, Yukon Denali XL
2007 GMC Sierra Classic, Sierra HD Classic
2003–2006 HUMMER H2
Vehicles with 4.8L, 5.3L, 6.0L or 8.1L Gasoline Engine (VINs V, B, T, Z, N, V, G – RPOs LR4, L33, LM7, L59, LQ9, LQ4, L18)
IMPORTANT: This Repair/Service Procedure is excerpted from a Technical Service Bulletin published by the vehicle manufacturer, and is intended for use by trained, professional technicians with the knowledge, tools and equipment to do the job properly and safely. It is recommended that this procedure not be performed by “do-it-yourselfers.”
ENGINE / MODEL
4.8L or 5.3L engine, 1500 Series Base Utility Trucks ONLY
Muffler Heat Shield – 24-inch
6.0L engine (LQ4, LQ9) H2 or 1500 Series Luxury Utility Trucks ONLY
Muffler Heat Shield – 28-inch
6.0L or 8.1L engine (LQ4, LQ9, L18) 2500 Series Utility, HD Pickups and Luxury Pickup Trucks ONLY
Muffler Heat Shield – 25-inch
6.0L or 8.1L engines ONLY
Clamp, Exhaust Pipe
Strap, Muffler Heat Shield
25 Series Suburban/Avalanche and 8600 lb. 25 Series Pickups w/LQ4)
Clamp, Exhaust Pipe – 2.75″ pipe
25 & 35 HD Pickups w/LQ4 or L18 engines
Clamp, Exhaust Pipe – 3″ pipe
Review safety procedures in ALLDATA Repair before beginning.
DON’T DO THIS
Install a new heat shield and straps on the existing muffler.
DO NOT replace the exhaust system components other than the muffler heat shield.
Raise and support the vehicle using factory and/or industry standard approved practices.
In order to avoid being burned, do not service the exhaust system while it is still hot. Service the system when it is cool.
Always wear protective goggles and gloves when removing exhaust parts as falling rust and sharp edges could result in serious personal injury.
Remove the nuts securing the muffler to the catalytic converter.
On 6.0L and 8.1L equipped vehicles only, loosen the exhaust pipe clamp.
Do not use oil base lubricants on the rubber exhaust hangers.
Apply a soapy solution to the exhaust pipe hanger rods in order to ease the removal of the exhaust hangers.
Pry the exhaust hangers free from the exhaust pipe hanger rods.
It is not necessary to remove the muffler from the vehicle to replace the muffler heat shield.
Reposition the muffler to gain access to the muffler heat shield.
Use extreme caution not to damage the muffler when removing the heat shield from the muffler.
Using an air-powered hack saw blade, or equivalent, cut off the existing muffler heat shield just as the heat shield rises off of the muffler (Figure 1).
Remove the heat shield from the muffler.
Hammer flush the remaining heat shield to the muffler (Figure 2).
The new heat shield should not come in contact with the remaining muffler heat shield. The new heat shield should not come in contact with the horizontal lock seam on the muffler.
Install the new heat shield (see parts information) onto the muffler (Figure 3).
Install three straps, P/N 10391259, so that the strap screw head will be located on top of the muffler.
Tighten the strap screw to 35 lb in (4 N.m).
Cut off the excess strap material and bend the strap over the strap screw head (Figure 4).
Remove the exhaust pipe clamp.
ONLY 6.0L and 8.1L equipped vehicles require a new exhaust pipe clamp, P/N 15103174.
On 6.0L and 8.1L equipped vehicles only, install a new exhaust pipe clamp, P/N 15103174, on the exhaust pipe.
Reposition the muffler in the correct position.
Slide the muffler forward into position, aligning the studs with the rear of the catalytic converter.
Install the nuts securing the muffler to the catalytic converter, but DO NOT tighten at this time.
Apply a soapy solution to these areas in order to ease the installation of the hangers:
The inner diameter of the exhaust pipe hanger
The exhaust pipe hanger rod
Press the exhaust pipe hangers over the exhaust pipe hanger rods.
Tighten the muffler nuts by hand until each contacts the metal flange.
Tighten the muffler nuts to 33 lb ft (45 N.m).
On 6.0L and 8.1L equipped vehicles only, tighten the exhaust clamp to 36 lb ft (50 N.m).
Lower the vehicle and test drive it to confirm the repair.
Authors: Ed Dorowski has 19 years of Domestic and Import dealership and independent shop experience as a service consultant, ASE Certified Master Technician, Nissan® Certified Master Technician, & California Smog Test & Repair Technician. Jeff Webster has 20 years of experience as a writer/editor.
GM, General Motors, Cadillac, Escalade, Escalade EXT, Escalade ESV, Chevrolet, Avalanche, Suburban, Tahoe, Silverado, Silverado HD, Silverado Classic, Silverado HD Classic, GMC, Sierra, Sierra HD, Yukon, Yukon Denali, Yukon Denali XL, Sierra Classic, Sierra HD Classic and HUMMER H2 are registered trademark names and model designations of General Motors Corporation. Nissan is a registered trademark of Nissan Motor Co. Ltd. All trademark names and model designations are being used solely for reference and application purposes.