Exhaust Gas Recirculation: Description and Operation
Fig 1 EGR Valve And Components:
NOTE: The Transitional Low Emission Vehicle (TLEV) EGR system is used with the 5.9L diesel engine when equipped with a California emissions package only.
PURPOSE
The EGR system reduces oxides of nitrogen (NOx) in the engine exhaust. This is accomplished by allowing a predetermined amount of hot exhaust gas to recirculate and dilute the incoming fuel/air mixture. This dilution reduces peak flame temperature during combustion.
EGR SYSTEM OPERATION
The system consists of:
- An EGR valve assembly. The valve assembly is located at the front of intake manifold (Fig. 1). The EGR valve is a poppet style valve (on/off only) and is controlled by an internal diaphragm.
- An EGR valve vacuum regulator solenoid. The solenoid is located at the front/top of cylinder head (Fig. 1) and will control the on-time and off-time of the EGR valve. A vacuum transducer is not used with this solenoid (EGR valve will be fully open or fully closed).
- The Powertrain Control Module (PCM) to operate the EGR valve vacuum regulator solenoid.
Fig 2 Engine Coolant Temperature Sensor:
- The Engine Coolant Temperature (ECT) sensor (Fig. 2) to supply an engine coolant temperature input to the PCM.
Fig 3 Intake Manifold Air Temperature Sensor:
- The Intake Manifold Air Temperature (MAT) sensor (Fig. 3) to supply an intake manifold air temperature input to the PCM.
Fig 4 Throttle Position Sensor -- Typical:
- The Throttle Position Sensor (TPS) (Fig. 4) to supply a voltage reference input to the PCM. This wilt tell the PCM how far the throttle has been opened. If equipped with the California Emissions Package (with EGR system), the TPS will be used with both automatic and manual transmissions.
- Unique exhaust and intake manifolds.
- An EGR tube (Fig 1) connecting a passage in the EGR valve to the rear of the exhaust manifold.
Fig 5 Engine Vacuum Pump:
- A vacuum pump to supply vacuum for the EGR valve vacuum regulator solenoid and EGR valve. The pump also supplies vacuum for operation of the power brake booster, speed control servo and the heating/air conditioning system. The crankshaft gear driven pump is located at the front of engine and is attached to power steering pump (Fig. 5).
- A quick-release one-way check valve (Fig. 1) to provide a fast release of engine vacuum from EGR valve diaphragm when EGR system is shut down.
- Vacuum lines and hoses to connect the various components.
When the PCM supplies a ground signal to the EGR valve vacuum regulator solenoid, EGR system operation starts to occur The PCM will monitor and determine when to supply and remove this ground signal. This will depend on inputs from the engine coolant temperature, throttle position and intake manifold air temperature sensors.
When the ground signal is supplied to the EGR solenoid, vacuum from the vacuum pump will be allowed to pass through the EGR solenoid and on to the EGR valve with a connecting hose.
Exhaust gas recirculation will begin in this order when:
- The engine is running to operate the vacuum pump.
- The powertrain control module (PCM) determines that engine coolant temperature is more than 140~ F but less than 220~ F and intake manifold air temperature is more than 20~ F but less than 170~ F.
- A ground signal from the PCM is supplied to the EGR solenoid.
- Vacuum passes through the EGR solenoid to the EGR valve diaphragm.
- The inlet seat (poppet valve) at the bottom of the EGR valve opens to dilute and recirculate exhaust gas back into the intake manifold.
The EGR system will be activated at engine idle speed. This is if PCM operating parameters for EGR system operation have been met.
The EGR system will be shut down briefly if the PCM has determined that a rapid acceleration is occurring. This is determined by a change in TPS voltage (mechanical throttle movement). The PCM will leave the EGR system shut down for a few additional seconds after the throttle has been depressed.
The EGR system will also be shut down for wide open throttle (WOT) conditions.
The EGR system will also be shut down by the PCM if the PCM has not sensed a TPS voltage change (mechanical throttle movement) after 2 continuous minutes. This shut down may occur at either engine idle speed or normal cruising speeds.
Each time the engine is operated, an on-board diagnostic test will be run to verify EGR system operation. Certain failures will illuminate the MIL (Malfunction Indicator Lamp). The MIL is indicated on the instrument panel as the Check Engine Lamp. Refer to the On-Board Diagnostics section for additional information. Also refer to the appropriate Powertrain Diagnostic Procedures.