Ford Mustang/Capri 1979-1988 Repair Guide

Underbody Catalytic Converter


See Figures 1, 2 and 3

Underbody catalytic converters were designed in a variety of shapes and sizes. Although their placement and positioning does vary, they are all designed to convert noxious emissions of hydrocarbons and and carbon monoxide into harmless carbon dioxide and water. For further information on emission controls, see Emission Controls .

Although most vehicles utilize a single underbody converter, some vehicles are also equipped with one or two light-off converters. These auxiliary converters are typically part of the inlet pipe or Y-pipe assembly, but on some vehicles, they are separate components. Removal and installation of these separate converters is covered below.


  1. Disconnect the negative battery cable.
  3. Raise and safely support the vehicle using jackstands placed under the frame.
  5. Remove the exhaust shield(s), if so equipped.
  7. Support the exhaust system to prevent component damage during removal.
  9. Disconnect the downstream injection air hose at the check valve, if so equipped.
  11. Separate the underbody converter from its adjacent components. This can be done by removing flange mounting bolts or pipe clamps, as equipped.
  13. Slide the muffler inlet pipe rearward, if necessary, and remove the converter.
  15. Installation is the reverse of removal. Always use new clamps and replace old gaskets. Always install all parts loosely and align the system, making sure that all clearances between the system parts and surrounding components are adequate. Torque support bracket bolts to 14 ft. lbs., flange nuts to 30 ft. lbs. and manifold nuts to 35 ft. lbs.

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Fig. Fig. 1: The underbody catalytic converter is typically located between the front exhaust pipe and the muffler inlet pipe

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Fig. Fig. 2: The front exhaust pipe is sometimes integral with the catalytic converter

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Fig. Fig. 3: Replace old gaskets, where applicable, and torque fasteners to the recommended specifications