DESCRIPTION
Note. For 6.2L light duty emission, also refer to the DIESEL ELECTRONIC CONTROL SYSTEM article in COMPUTERIZED ENGINE CONTROLS section.
Purpose of the Exhaust Gas Recirculation (EGR) system is to limit formation of oxides of nitrogen (NOx) emissions. This is done by reducing peak combustion chamber temperatures during which NOx is formed. This is accomplished by reintroducing a small mount of exhaust gas into the combustion chamber, diluting the air/fuel mixture and thereby reducing NOx formation.
EGR system consists of EGR valve, Exhaust Pressure Regulator (EPR) valve and EGR/EPR solenoid assembly.
OPERATION
The ECM controls EGR by controlling amount of "on" and "off" time of EGR solenoid using input from engine speed sensor and TPS. The ECM uses input from the MAP sensor to measure amount of absolute pressure in EGR vacuum line. If a minor variation between calculated EGR and actual EGR is monitored by ECM, the ECM will make a correction. If variation is too great for ECM to correct, an error is detected. The ECM will go then into default.
When EGR is not needed, the EGR vent solenoid is energized by the ECM to vent vacuum. The ECM also energizes EPR solenoid to close EPR valve at idle to lower exhaust backpressure.
Scheme 184
Scheme 185
SYSTEM TESTING
Note. Testing information not available.