Exhaust System: Overview RAM Pickup 2500

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The Federal Gasoline Engine Exhaust System Consists Of Engine Exhaust Manifolds, Exhaust Pipes, Catalytic Converter (S), Extension Pipe (If Needed), Exhaust Heat Shields, Muffler And Exhaust Tailpipe.

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The California Emission Vehicles Exhaust System Also Contains The Above Components As Well As Mini Catalytic Converters Added To The Exhaust Pipe.

The Exhaust System Must Be Properly Aligned To Prevent Stress, Leakage And Body Contact. Minimum Clearance Between Any Exhaust Component And The Body Or Frame Is 25.4 Mm (1.0 In.). If The System Contacts Any Body Panel, It May Amplify Objectionable Noises From The Engine Or Body.

EXHAUST SYSTEM DIAGNOSIS CHART

DESCRIPTION

There are two catalytic converters welded to the front exhaust pipe (1) near each bank inlet. One converter collects the exhaust from the right bank and a second one collects the exhaust from the left bank. The catalytic converters are not serviceable separate from the front exhaust pipe. If either catalytic converter requires service, the front pipe will need to be replaced Refer to PIPE, Exhaust , Removal .

OPERATION

The catalytic converter captures and burns any unburned fuel mixture exiting the combustion chambers during the exhaust stroke of the engine. This process aids in reducing emissions output.

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1. Raise and support vehicle.
2. Saturate the bolts and nuts with heat valve lubricant. Allow 5 minutes for penetration.
3. Disconnect oxygen sensor electrical connectors.
4. Remove clamp (4).
5. Remove bolts exhaust to manifold (2).
6. Remove catalytic converter (3).

Scheme 6

1. Raise and support the vehicle.
2. Saturate the bolts and nuts with heat valve lubricant. Allow 5 minutes for penetration.
3. Disconnect flexible exhaust differential pressure sensor tubing (2).
4. Remove exhaust pressure differential sensor tubing from NOx Absorber Catalyst (NAC) (1).
5. 4X4 Vehicles - Remove transfer case skid plate. Refer to «PLATE, Skid, Front , Removal»(ref-457829-S37099224772012030200000) and «PLATE, Skid, Transfer Case , Removal»(ref-457829-S06628527422012030200000) .
6. 4X4 Vehicles - Remove transmission crossmember. Refer to «CROSSMEMBER, Lower Control Arm , Removal»(ref-457829-S02998048772012030200000) and «CROSSMEMBER, Transmission , Removal»(ref-457829-S13491836922012030200000) .
7. Remove Diesel Particulate Filter (DPF) to NOx Absorber Catalyst (NAC) flange nuts (7).
8. Remove NAC to Diesel Oxidation Catalyst (DOC) to NAC flange nuts (5).
9. Remove NAC (7) from isolators.
10. Remove NAC and discard gaskets.
11. Remove DOC to turbocharger clamp at turbocharger (3).
12. Remove DOC (4) from vehicle and discard gasket.

1. The Aftertreatment System consists of three catalyst elements, all working together to drastically reduce tailpipe emissions

The oxidation catalyst raises the exhaust gas temperatures to regenerate the DPF, which is passive regeneration. If the passive regeneration cannot keep up with the build up of soot in the DPF, the ECM will actively regenerate the DPF to burn off the soot. Residue remains inside the DPF in the form of non burnable ash. Ash comes from the oils and other materials that are trapped in the oils and are present in the soot. The catalyst contains a large number of parallel channels, which run in the axial direction and are separated by thin porous walls. The channels are alternatively open at one end, but plugged at the other. The exhaust gases flow through the walls and escape through the pores in the wall material. Particulates, however, are too large to escape and are trapped in the monolith walls. The ECM starts the regeneration of the DPF if the soot load exceeds a performance map value. The ECM determines the load condition of the DPF based upon the exhaust gas pressure upstream and downstream of the DPC/DPF. A pressure differential sensor provides the pressure input to the ECM. During the regeneration process, the ECM raises the temperature in the DOC/DPF to burn off the soot accumulated. Under normal operation, the engine does not produce enough heat to oxidize the soot inside the DOC/DPF. This process requires temperatures above 550 oC (1,022 oF). After regeneration, the ECM reads the actual pressure difference at the DOC/DPF and compares it with a reference value. From this comparison, the ECM determines the ash quantity inside the DOC/DPF.

When the exhaust gas temperature is cold, the sensor resistance is high, the Engine Control Module (ECM) will sense the resistance and sense the exhaust temperature as cold.

When the exhaust gas temperature is high, the sensor resistance is low, the ECM will sense the resistance and sense the exhaust temperature as high.

There are two types of heat shields used. One is stamped steel the other is molded foil sheets. The shields attach to the vehicle around the exhaust system to prevent heat from the exhaust system from entering the passenger area and other areas where the heat can cause damage to other components.

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1. Raise and support the vehicle. 1 - HEAT SHIELD 2 - FASTENER 3 - NUT 4 - HEAT SHIELD
2. Remove the nuts (3) or bolts (2) holding the exhaust heat shield (1) to the floor pan, crossmember or bracket. (Scheme 7) see scheme 43 see scheme 42 1 - HEAT SHIELD 2 - NUT
3. Slide the shield (1) out around the exhaust system.