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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 687 (ENGINE EXHAUST SYSTEM)REPAIR INSTRUCTIONSCATALYTIC CONVERTER REPLACEMENT (3.8L)INSTALLATION PROCEDURE
1999 GMC Forward Control 5.7 R, Automatic

Installation Procedure

1999 GMC Forward Control 5.7 R, AutomaticSECTION Installation Procedure
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
  1. Install the heated oxygen sensor (HO2S). Refer to HEATED OXYGEN SENSOR in Engine Performance - Removal & Installation
    NOTE: To prevent internal damage to the flexible coupling of the catalytic converter assembly, the converter must be supported. The vertical movement at the rear of the catalytic converter assembly must not exceed 6 degrees up or down.
  2. Install a new gasket to the exhaust pipe studs.
  3. Install and support the 3-way catalytic converter.
    NOTE: Refer to FASTENER NOTICE in Cautions and Notices.
  4. Install the catalytic converter nuts.

    Tighten 

    Tighten the nuts to 60 N.m (44 lb ft).

    Fig 1: Installing Catalytic Converter Nuts
    G02080724Courtesy of GENERAL MOTORS CORP.
  5. Install a new exhaust manifold pipe gasket.
  6. Install the exhaust manifold pipe stud nuts.

    Tighten 

    Tighten the nuts to 35 N.m (26 lb ft).

    Fig 2: Installing Exhaust Manifold Pipe Stud Nuts
    G02080725Courtesy of GENERAL MOTORS CORP.
  7. Install the catalytic converter hangers.
  8. Remove the support from the exhaust system.
  9. Connect the heated oxygen sensor (HO2S) electrical connector.
  10. Inspect the exhaust system for leaks and underbody contact.
  11. Lower the vehicle.
    Fig 3: Installing Catalytic Converter Hangers
    G02080726Courtesy of GENERAL MOTORS CORP.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.