Exhaust Emission Control System

The exhaust gas recirculation (EGR) system is designed to:

• Reintroduce exhaust gas into the combustion cycle.
• Lower combustion temperatures.
• Reduce the formation of Nitrous Oxide.

The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration. Timing and volume are controlled by:

• Engine rpm.
• Engine vacuum.
• Exhaust system back pressure.
• Engine coolant temperature.
• Throttle position.

The EGR valve (EGR valve) (9D475) is vacuum actuated. The vacuum hose routing diagram is shown on the Vehicle Emission Control Information (VECI) decal.

The EGR systems used are pressure feedback EGR (PFE/DPFE) systems. PFE is a subsonic closed loop EGR system. The DPFE system:

• Monitors EGR flow rate by the pressure drop across a sharp-edged metering orifice.
• The PFE system uses EGR pressure valve sensor (9J460) as the feedback device.
• Controlled pressure is varied by the valve movement using vacuum output of the EGR vacuum regulator control (9J459) .
• Uses the EGR valve only as a pressure regulator, rather than a flow metering device.

The differential pressure feedback EGR (DPFE) system:

• Operates in the same manner as PFE.
• Directly monitors the pressure drop across the metering orifice.
• Allows for a more accurate assessment of EGR flow requirements.

Vehicle Emission Control Information Decal

Vacuum hoses on the engine use a color stripe to aid in hose routing checks. The stripe will usually be the same color as on the Vehicle Emission Control Information (VECI) decal, but the correct vacuum hose routing must be verified by using the correct component connections shown on the VECI decal.

Typical VECI Decal