Initial Inspection and Diagnostic Overview

1. Visually inspect the components of the Three Way Catalytic (TWC) converter and exhaust system and related controls that may affect exhaust gas quality, cause backfire, or loss of power.

Mechanical
- Leaking fuel injectors

- Damaged air inlet passages

- Inoperative Exhaust Gas Recirculation (EGR) valve

- Exhaust pipe pinched, crushed

- Damaged, loose vacuum hoses

- Incorrect idle speed

- Dirty air filter

- Damaged TWC

Electrical
- Misrouted, damaged wiring

- Damaged coil, distributor, or spark plugs

- Corroded, loose connectors

2. Exercise the wiring and connectors for the solenoids and other components for obvious problems due to looseness, corrosion, or other damage. This must be done after the engine is fully warmed so as to activate the system controls.

3. Check the vacuum lines and connections for looseness, pinching, leakage, splitting, blockage, or other damage that may cause malfunction.

4. If a vacuum line or orifice (restrictor) blockage is suspected as the obvious cause of malfunction, correct the cause before proceeding to the next step.

5. Check engine oil for fuel dilution.

6. If all checks are OK, proceed with Catalyst and Exhaust System Pinpoint Tests.

NOTE: Failure to conform to the Federal Clean Air Act legal requirements for a particular vehicle and calibration is usually the result of one or more emission related system or component malfunctions.

7. If the diagnostic symptom is Fails Emission Test, proceed to Pinpoint Test Perform Exhaust Emission Test. Perform Exhaust Emission Test

If the diagnostic symptom is Backfires or Lacks Power, proceed to Perform Vacuum Test. Perform Vacuum Test