EGR System Mitsubishi Mirage II

DESCRIPTION

All vehicles are equipped with an exhaust gas recirculation (EGR) system to reduce NOx emissions. The EGR system partially recirculates exhaust gases from an exhaust port of the cylinder head into a port at the intake manifold below the carburetor. EGR flow is controlled by the EGR control valve and thermo valve.

EGR CONTROL VALVES

The increased EGR flow required to meet emission standards adversely affects driveability. The EGR control valves compensate for the EGR's effect on driveability and are controlled by carburetor vacuum. The amount of vacuum is governed by relative throttle openings. The EGR system increases EGR flow during high load operation and decreases EGR flow during low load operation. Vacuum level at idle and wide open throttle is low and no EGR operation occurs in these modes. Two types of EGR valve systems may used to accomplish this

Single EGR Valve

Vehicles are equipped with the single EGR Valve System.

Sub EGR Control Valve

This mechanically controlled valve is linked to the throttle valve. This valve closely controls EGR flow by responding directly to throttle valve position.

THERMO VALVE

The Thermo valve senses engine coolant temperature and prevents EGR operation below preset values. When the engine warms up, the thermo valve opens, supplying vacuum to the EGR valve. At temperatures below 131°F (55°C) the thermo valve is open, the vacuum is vented and no vacuum is supplied to the EGR valve. At temperatures above 131°F (55°C) the thermo valve closes and normal EGR operation is accomplished.

SUB-EGR VALVE

1. Operate the sub EGR valve manually (pull valve open by hand). The valve should move smoothly through its full range of motion. If the valve operation is difficult, remove valve and inspect for carbon, dust and/or other deposits. If necessary, clean valve with solvent. Apply a light coat of oil.
2. If operation remains difficult after cleaning, replace the sub EGR valve. Before removing a sub EGR valve that is difficult to operate, spray with solvent several times from the outside with the rubber boot removed, then remove the valve.

Typical EGR Control Valve Configurations. Scheme 5

SYSTEM TESTING

1. Check hoses for proper routing and condition. Cold start engine and run at idle. Observe the EGR valve for operation as engine speed is increased to 2500 RPM. There should be NO EGR operation after cold start. If the EGR valve operates, replace thermo valve.
2. Warm engine until coolant reaches 185-194°F (85-90°C). Increase engine speed to 2500 RPM. Observe the EGR valve. The EGR valve should operate. If EGR is inoperative, check EGR valve and thermo valve. Replace as necessary.
3. Detach hose (Green stripe) from thermo valve. Connect vacuum pump and apply vacuum. If no vacuum is available through thermo valve, valve is defective. Replace as necessary.
4. Remove vacuum pump from thermo valve and reconnect hose (Green stripe) to thermo valve. Disconnect hose (Green stripe) from fitting at carburetor. Connect a vacuum pump to hose end.
5. Apply 9.8 in. Hg of vacuum while opening sub EGR valve (pull valve open by hand). If idle speed becomes unstable the EGR valve is okay. If idle speed remains stable the EGR valve is NOT okay. Replace EGR valve as necessary.
6. Remove the vacuum pump from hose end. Reconnect hose to carburetor. Disconnect the hose (Yellow stripe) from the EGR control valve. Connect vacuum pump to the fitting on the EGR control valve.
7. Apply 5.9 in. Hg of vacuum while opening the sub EGR valve (pull valve open by hand). If idle speed becomes unstable the EGR valve is okay. If idle speed remains stable the EGR valve is NOT okay. Replace EGR valve as necessary.
8. Remove vacuum pump from EGR control valve. Reconnect hose (Yellow stripe) to fitting of EGR control valve.