Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (1-5 psi) gauge to check exhaust system.

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

• Check At Oxygen Sensor  Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.
• Diagnosis 
  1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM. Note gauge. Exhaust system is restricted if reading exceeds 1.25 psi (.09 kg/cm² ).
  2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exists, check for restricted catalytic converter. Replace as required.