Emissions Control Systems Review

Emissions Control Systems: Key Concepts and Components

Abbreviations

  • EGR: Exhaust Gas Recirculation
  • EVAP: Evaporative Emissions Control System
  • AIR: Air Injection Reaction
  • PCV: Positive Crankcase Ventilation
  • HC: Hydrocarbons
  • CO: Carbon Monoxide
  • NOx: Nitrogen Oxides
  • TWC: Three-Way Catalytic Converter
  • DPFE: Delta Pressure Feedback EGR (sensor)
  • DTC: Diagnostic Trouble Code

Main Pollution Gases from Combustion

  • The three primary pollution gases produced by combustion that are targeted for reduction include:
    • Hydrocarbons (HC)
    • Carbon Monoxide (CO)
    • Nitrogen Oxides (NOx)

Emissions Legislation History

  • California: The first state to implement emissions laws, leading the way for federal regulations.

EGR System

  • Purpose: The primary function of the EGR system is to reduce NOx emissions by recirculating a portion of exhaust gases back into the intake manifold, which lowers combustion temperatures.

EVAP System Enhancements (OBD-II)

  • Components added to the basic EVAP system:
    • Purge valve
    • Vent valve
    • Fuel tank pressure sensor
  • These components help in leak testing of the EVAP system.

EGR Valve Operation

  • Monitoring Methods by PCM:
    • Changes in MAP sensor readings
    • DPFE sensor feedback
    • Observations of engine performance or idle.

PCV Valve Function

  • Purpose: The PCV valve allows venting of crankcase gases back into the intake manifold, promoting combustion of these gases, which reduces emissions and prevents oil contamination.

EVAP System Emission Control

  • The EVAP system specifically controls the emission of Hydrocarbons (HC).

Catalytic Converter Efficiency

  • Temperature Requirement: The catalytic converter becomes efficient at temperatures ranging from 500 to 600°F (260 to 315°C).

Vapor Canister Function

  • The vapor canister is designed to store fuel vapors from the fuel tank until they are purged and burned in the engine.

Leak Detection in EVAP System

  • Common Tool: The most useful tool for locating leaks in the EVAP system is a smoke machine (EVAP smoke tester).

AIR System Role

  • Function: The AIR system (Secondary Air Injection) sends additional oxygen to the catalytic converter, enhancing its efficiency.

NOx Formation Temperature

  • NOx forms in the combustion chamber at temperatures above 2500°F (1370°C).

Catalytic Converter Operation Check

  • Method: The PCM checks the catalytic converter operation by comparing the signals from the pre- and post-catalytic converter O2 sensors.

Greenhouse Gas Monitoring

  • Main Gas Responsible for Global Warming: Carbon Dioxide (CO₂) is primarily associated with greenhouse gases, though it is not directly monitored by OBD-II systems.

Carbon Monoxide Characteristics

  • Properties: Carbon Monoxide (CO) is odorless, colorless, and can be deadly.

Common Fueling Issues

  • Potential Problem: If the gas pump repeatedly shuts off during fueling, the most likely issue is a restriction in the EVAP vent system, possibly due to a clogged vent valve or canister.

Exhaust Temperature in Catalytic Converters

  • As exhaust passes through a properly functioning catalytic converter, its temperature should increase due to the oxidation of gases.

O2 Sensor Readings

  • Expected Behavior: In a properly operating converter, the pre-O2 sensor readings should fluctuate, while post-O2 sensor readings should be stable, indicating correct function.

EGR Valve Operation During Driving

  • The EGR valve should be open during cruising or part-throttle driving, but not during idle or full throttle conditions.

Vehicle Emissions Control Information (VECI)

  • The sticker found in the engine compartment containing emissions information is called the VECI label.

VVT and EGR System

  • The Variable Valve Timing (VVT) system can eliminate the need for an EGR system in some engines by managing internal EGR through valve overlap.

Vapor Canister Composition

  • Inside the vapor canister, activated charcoal absorbs and stores fuel vapors.

Catalytic Converter Testing Tools

  • Tools that can be used to test a catalytic converter include:
    • Infrared thermometer
    • Scan tool (for O2 sensor readings)
    • 5-gas analyzer

Check Engine Light Activation

  • Typically, it takes 2 consecutive drive cycles to trigger the Check Engine Light after an emissions-related problem occurs.

Common EVAP System Leak Locations

  • Areas most likely to experience leaks within the EVAP system that could set a Diagnostic Trouble Code (DTC) include:
    • Gas cap
    • Vent valve
    • Purge valve
    • Canister hoses
    • Fuel tank pressure sensor.