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KEEP IT CLEAN. KEEP IT QUIET.
Exhaust systems, particularly pipe and mufflers, are no longer common repair items. The use of aluminized and stainless steel has greatly extended the life of the exhaust system as we know it. Now, it is not uncommon for exhaust systems to last in excess of 10 years and/or 150,000 miles. Problems still occur, but less often than in the past. One component of the exhaust system that still sees problems is the catalytic converter. Many of these problems are due to contamination.
TYPICAL EXHAUST SYSTEM
Most connections on the modern exhaust are welded, not connected with band clamps. The exhaust manifolds are equipped with ball flange outlets to assure a tight seal and strain-free connection with the mounting flanges. The exhaust system must be properly aligned to prevent stress, leakage and body contact. If any part of the exhaust system contacts the heat shields, or a section of the floorplan, it can amplify noises coming from the engine or body.
The biggest difference between the exhaust system on the modern car and one that was built 30 years ago is the material. There was a time, not long along, when virtually all exhaust pipe was made from plain carbon steel. It was inexpensive to make (about 25 cents a foot), but it rusted. It was a time when muffler shops were as common as today’s oil change stores, because the original muffler and exhaust system did not last the life of the car. Not even close.
All that changed when automakers started using aluminized and stainless steel. These new steels did not rust like the old carbon steel exhaust pipe. In some cases, the exhaust system began to last the life of the car. Before long, all of the muffler shops disappeared. This is not to say that problems with exhaust no longer exist, but exhaust pipe and muffler replacement is no longer considered regular maintenance.
EXHAUST SYSTEM PROBLEMS
There are two main objectives of the modern exhaust system — to reduce the exhaust noise to an acceptable level and to reduce emission levels as the exhaust gas passes through the catalytic converter(s). The first sign of a problem with the exhaust system is, obviously, noise. Other common exhaust problems are revealed by leaks and restrictions. If emission levels become excessive, the catalytic converter is likely to be the source of the problem. And, the main cause of converter failure is contamination.
When inspecting an exhaust system, look closely for cracked or loose joints, stripped screw or bolt threads, corrosion damage and worn, cracked or broken hangers. Replace all components that are badly corroded or damaged. Do not attempt to repair rusted components.
Exhaust noise is commonly the result of a leak at an exhaust pipe joint. Many of these joints are welded, as can be seen at (Figure 2) (A) (B) (C) (D) and (E). While this noise is not as loud as a rusted out muffler, it’s loud enough to be annoying. These leaks can be found by pressurizing the exhaust system. Often, such leaks can be corrected by re-welding the damaged joint.
Restrictions in the exhaust system can be found by measuring the back pressure. This test requires the use of a scan tool and PEP module pressure tester. The procedure is detailed in the specific service manual for the vehicle being repaired.
Note: The normal operating temperature of the exhaust system is very high; never work around or attempt to service any part of the exhaust system until it has cooled; special care should be taken when working near the catalytic converter.
AFTERMARKET EXHAUST COMPONENTS
When exhaust components require replacement, it is very important to use O.E. parts. The simple truth is that aftermarket exhaust components just don’t last as long as the O.E. replacement parts. And, aftermarket mufflers are noisy. It is true that aftermarket parts are sometimes cheaper than O.E. parts, but these components do not meet O.E. standards for fit, quality and performance. This is particularly true of catalytic converters. Don’t short-change your customers. Use Mopar® replacement parts for all of your exhaust repair jobs.
3.6L V6 ENGINE
Since 2011, the 3.6L V6 engine has become the standard engine used across much of the FCA US LLC product line. Due to this engine’s popularity, you should become familiar with its design. It’s interesting to note that the exhaust system has a unique feature. The exhaust manifold is integral with the cylinder head. And, the catalytic converter is bolted directly to the cylinder head (Figure 3). This design essentially removes a major component from the exhaust system; namely, the exhaust manifold. As a result, any potential exhaust leaks between the exhaust manifold and cylinder head are eliminated.
This design also includes a unique mounting configuration. Often, ball flange outlets are used to connect catalytic converters. On this engine, however, a steel retainer plate (Figure 3) is used to hold the lower section of the flange, while two bolts are used to secure the upper section of the flange to the integrated exhaust manifold. The lower section of the converter flange actually sits in a lip on the retainer plate.
To remove the catalytic converter, disconnect the temperature and oxygen sensor electrical connectors. Then, remove the two upper converter-to-exhaust manifold bolts. Remove the catalytic converter by lifting and sliding the flange up and away from the exhaust manifold. The retainer plate does not need to be removed.
If new gaskets are being used, the retainer plate must be removed. Position the new gasket onto the manifold flange and install the lower retainer plate. Loosely install all four bolts to align the gasket, then tighten lower retainer bolts 27 ft. lbs. Remove the upper bolts.
Install the new catalytic converter by lowering and sliding the flange down and toward the exhaust manifold. Install the upper flange bolts, then tighten upper bolts 27 ft. lbs. Re-connect the temperature and oxygen sensor electrical connectors.