Cummins ISX11.9 CM2250 – Service Manual 011-062   Aftertreatment Decomposition Tube

The decomposition tube is the section of the exhaust pipe between the aftertreatment diesel particulate filter and aftertreatment selective catalytic reduction (SCR) catalyst. The aftertreatment decomposition tube is designed to help atomize and mix the diesel exhaust fluid (DEF) being sprayed into the exhaust stream for complete NOx conversion.

The aftertreatment decomposition tube is composed of two important areas.

1. The aftertreatment DEF dosing valve mount – the position at which the aftertreatment DEF dosing valve is mounted and allowed to spray DEF into the exhaust stream.
2. The aftertreatment decomposition tube mixer – creates a swirl pattern exhaust stream to help mix the DEF and engine exhaust.

Different vehicles will require different aftertreatment configurations. Some of the aftertreatment decomposition tubes may have elbows clamped to either end of the tube.

A variation in vehicle aftertreatment configurations will drive the aftertreatment to have different flanges. The clamps and gaskets on either end of the aftertreatment decomposition tube may vary from one another.

There are two types of flanged joints, spherical Marmon™ and full Marmon™.

The spherical Marmon™ joints allow a small amount of misalignment and have a rounded cross section.

The full Marmon™ joints are completely rigid and have a more edgy profile.

Inspect all the joints for any signs of leaks. Leaking DEF will leave white deposits.

If a DEF leak is found, reference the Clean and Inspect for Reuse section of this procedure.

WARNING  During regeneration, exhaust gas temperature could reach 800°C [1500°F], and exhaust system surface temperature could exceed 700°C [1300°F], which is hot enough to ignite or melt common materials, and to burn people. The exhaust and exhaust components can remain hot after the vehicle has stopped moving. To avoid the risk of fire, property damage, burns or other serious personal injury, allow the exhaust system to cool before beginning this procedure or repair and make sure that no combustible materials are located where they are likely to come in contact with hot exhaust or exhaust components.

WARNING  Batteries can emit explosive gases. To reduce the possibility of personal injury, always ventilate the compartment before servicing the batteries. To reduce the possibility of arcing, remove the negative (-) battery cable first and attach the negative (-) battery cable last.

WARNING  Wear appropriate eye and face protection when using compressed air. Flying debris and dirt can cause personal injury.

CAUTION  The aftertreatment DEF dosing valve is a fragile item. Use great care when handling this part. Avoid putting stresses on the fluid connectors as damage to the component may result.

• Disconnect the batteries. Refer to the OEM service manual.
• Use shop air to clean the area and remove any debris from the aftertreatment decomposition tube.
• Remove the aftertreatment DEF dosing valve from the aftertreatment decomposition tube. Refer to Procedure 011-059 in Section 11.

NOTE: It is acceptable to remove the aftertreatment dosing valve without removing the DEF and coolant lines.  However, support the aftertreatment DEF dosing valve. Do not let it suspend freely, or it can damage the fluid connectors and lines.

CAUTION  Do not use an air tool to remove the V-band clamp nut. An air tool will damage the threads. Apply thread lubricant to the V-band clamp threads prior to nut removal.

NOTE: Before removing the aftertreatment decomposition tube, note the location and orientation of the aftertreatment decomposition tube and related components. Apply identifying markings to aid in installation.

Remove the exhaust clamps from both ends of the aftertreatment decomposition tube.

NOTE: In some applications the aftertreatment decomposition tube may be welded to the aftertreatment SCR or aftertreatment elbow.

NOTE: Depending on the exhaust configuration, it may be necessary to loosen exhaust hangers, remove addition elbows, exhaust piping, and securing the rest of the aftertreatment before removing the aftertreatment decomposition tube.

Remove the aftertreatment decomposition tube.

Discard the gaskets.

Inspect the aftertreatment DEF dosing valve mount  for a buildup of crystallized DEF.

Inspect the decomposition tube mixer for a buildup of crystallized DEF.

Inspect the inlet of the aftertreatment SCR catalyst for buildup.  Refer to Procedure 011-036 in Section 11.

Inspect the outlet of the DPF for crystallization. Refer to Procedure 011-074 in Section 11.

Inspect any additional elbows or exhaust pipes connected to the aftertreatment decomposition tube for DEF buildups.

If the crystallization is excessive and blocking a majority of the exhaust passages, there may be a problem with the aftertreatment DEF dosing valve.

NOTE: Prior to performing this test, if not already directed by a fault code troubleshooting tree, view and troubleshoot any fault codes with INSITE™ electronic service tool. Use the ISX15 CM2250 Fault Code Troubleshooting Manual, Bulletin 4022225.

If there are not any fault codes present, use the following procedure to perform a test of the aftertreatment DEF dosing valve. Refer to Procedure 011-063 in Section 11.

CAUTION  Do not use a metallic object to clean the aftertreatment decomposition tube.  This will scratch the surface of the aftertreatment decomposition tube which may cause future excessive DEF crystallization buildup.

If buildups are present, carefully scrape with a non-metallic object to clean the majority of the buildup.

Use a pressure washer to dissolve the remaining crystallization.

NOTE: If crystallization buildup is present, complete a stationary regeneration after installation to make sure that any of the remaining DEF crystallization is removed from the aftertreatment decomposition tube.

Inspect the exhaust flanges for corrosion or other damage.

Use a putty knife to remove any residual gasket material from the flanges on the aftertreatment decomposition tube.

Do not grind on the flange surface. Grinding the surface can damage the flange and cause the connection to leak.

Inspect the V-band clamps and mounting straps for signs of over-extension.

The band must not be bent or damaged.

Inspect the V-band clamp and mounting strap threads for damage.

Replace the V-band clamp or mounting strap if damage is found.

Inspect the aftertreatment DEF dosing valve mounting area. Check the threaded capscrew holes for damaged threads. If the capscrew holes are damaged, the aftertreatment decomposition tube can be repaired. 

Coiled thread insert or inner coil threads, M6X1, can be used to repair any damaged threads. Bore the hole 12 mm [0.47 in] deep and install the threaded coil. 

Use only the wire type coil inserts since the amount of material around the threaded capscrew hole is limited.

Follow the manufacturer recommended guidelines to install the coiled threaded insert.

NOTE: The aftertreatment decomposition tube must be smooth and free of scratches or damage.

If the aftertreatment decomposition tube has any structural defects or material degradation, replace the aftertreatment decomposition tube.

Look at the following areas:

1. Aftertreatment dosing valve mount
2. Mixer
3. Insulation
4. Welded joints.

NOTE: The gaskets and clamps on either end of the aftertreatment decomposition tube may not be the same. Reference the General Information section of this procedure.  Where applicable, install and tighten the full Marmon™ clamps before the spherical Marmon™, to account for misalignment in the aftertreatment system.

Use new gaskets and install the aftertreatment decomposition tube.

If other parts of the aftertreatment system were adjusted in the removal process of the aftertreatment decomposition tube, slide them back into position.

Align the aftertreatment decomposition tube using the identification marks that were made before removal.  If the marks are not present, use the next step for appropriate orientation of the aftertreatment decomposition tube.

Apply a coat of anti-seize compound on the threads of the V-band clamps.

Install and tighten the V-band clamps.

Verify the aftertreatment decomposition tube is installed in the same orientation as it was removed.

As viewed from the inlet/outlet of the aftertreatment decomposition tube, the aftertreatment DEF dosing valve mount must be placed between ± 45 degrees and ±85 degrees.

WARNING  Batteries can emit explosive gases. To reduce the possibility of personal injury, always ventilate the compartment before servicing the batteries. To reduce the possibility of arcing, remove the negative (-) battery cable first and attach the negative (-) battery cable last.

• Tighten any aftertreatment hangers that may have been loosened in the removal process. Refer to OEM service manual.
• Install the aftertreatment DEF dosing valve. Refer to Procedure 011-059 in Section 11.
• Connect the batteries. Refer to the OEM service manual.
• Operate the engine and check for exhaust leaks.
• If buildups were present, complete a stationary regeneration to be sure that any of the remaining DEF crystallization has been removed from the aftertreatment.
• Continue to monitor for leaks at the exhaust joints.