Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. The exhaust system can be checked with a vacuum gauge or a 1-10 psi pressure gauge.

If a vacuum gauge is used, connect it to intake manifold vacuum and start engine. Observe gauge and hold throttle steady at 2000-2500 RPM. If vacuum gauge reading slowly drops after stabilizing, exhaust system may be restricted.

• Check at AIR Pipe  Remove rubber hose at exhaust manifold AIR pipe check valve and remove check valve. Install pressure gauge to hose and nipple via Propane Enrichment Device (J26911). Nipple should be inserted into exhaust manifold AIR pipe.
• Check at O2 Sensor  Remove O2 sensor. Install backpressure tester in place of O2 sensor. After test is completed, coat O2 sensor threads with anti-seize compound.
• Diagnosis 
  1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. Reading should not exceed 1.25 psi (.09 kg/cm² ). Exhaust system is restricted if specification is exceeded.
  2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as required.