Exhaust Gas Recirculation System (EGR)

Overview

• Covers information about the EGR system, functional test, and smog check inspection procedures.
• Not a replacement for Smog Check or Automotive Repair Act laws and regulations.
• Review basic operation of EGR valves.
• Describe EGR testing procedures.
• Use videos for demonstration during smog check inspection.

Importance of EGR

• Reduces peak combustion temperatures.
• Helps lower NOx emissions, reducing photochemical smog and ground-level ozone.

Basic Operation

• Recirculates a portion of exhaust gas back into the combustion chamber.
• This inert gas displaces part of the fuel charge, lowering combustion temperatures.

EGR Testing Procedures

• Vary greatly between systems.
• Critical to use all available resources and references.
• Refer to the latest smog check manual on BAR's website for test requirements.

Types of EGR Systems

1. Ported Vacuum

   • Uses a vacuum port above the throttle plate.
   • Vacuum applied as throttle plates open.
   • Controlled by engine's temperature (coolant temperature switch).
   • Closes under hard acceleration.

2. Venturi Vacuum

   • Controlled by vacuum from carburetor or throttle body.
   • Highly sensitive, provides accurate control.

3. Back Pressure Valves

   • Negative Back Pressure: Vacuum bleed determined by exhaust pulses.
   • Positive Back Pressure: Uses exhaust pressure to regulate flow.

4. Computer Controlled

   • Adjusted by vehicle's computer based on sensor inputs (coolant temp, throttle position, etc.).

5. Digital EGR Systems

   • Operate without engine manifold vacuum.
   • Controlled by ECM using electric solenoids.

EGR Testing Example

1995 Ford Taurus 3.8L V6

• Actuated by vacuum via EVR solenoid, controlled by PCM.
• Uses a duty cycle to regulate vacuum level.
• Requires ECS application guide for test procedures.
• Test Procedure #11: Includes visual and functional checks.
  • Handheld vacuum pump and tachometer needed.
  • Ensure vacuum hoses are properly routed and connected.
  • Check vacuum supply: should be < 1 inch at idle.

1995 Oldsmobile Delta 88 3.8L V6

• Linear EGR valve controlled electronically by PCM.
• Requires a scan tool for functional testing.
• Test Procedure #27: Use scan tool to actuate valve and check diagnostics.
  • Manually cycle EGR valve from 0 to 100%.
  • Listen for RPM drop, indicating open EGR valve.

Conclusion

• Understanding of EGR systems and testing is crucial.
• Recognize types, test requirements, and know how to use ECS guides.
• Module 8 of California Smog Check Program Training Series provides foundational knowledge.