DESCRIPTION
To reduce NOx emissions, all vehicles are equipped with an Exhaust Gas Recirculation (EGR) system. The EGR system recirculates exhaust gases from an exhaust port in the cylinder head to a port in the intake manifold located below the carburetor. EGR flow is controlled by the EGR valve, thermo valve, EGR solenoid valve (turbocharged models), or vacuum regulator valve (carbureted models).
EGR CONTROL VALVE
The EGR control valve compensates for the EGR system's effect on driveability. The EGR system increases EGR flow during high load operation and decreases during low load operation. There is no EGR operation at idle or wide open throttle. Three types of EGR valves are used. (Scheme 9)
Scheme 9
EGR CONTROL SOLENOID VALVE
The pressure applied to EGR control valve is controlled by the solenoid valve. The solenoid valve mixes throttle ported pressure with turbocharged pressure from ECU information based on coolant temperature and engine speed.
THERMO VALVE
The thermo valve senses engine coolant temperature which prevents EGR operation below preset values. At temperatures below 140°F (60°C) thermo valve is open and vacuum is vented so no vacuum is supplied to the EGR valve. At temperatures above 140°F (60°C) the thermo valve closes and normal EGR operation takes place.
Colt, Raider & Ram-50
- Disconnect Green-striped hose from throttle body and connect vacuum pump to hose end. When engine is cold, 113°F (45°C) or less, and at 3500 RPM, apply vacuum to hose. If vacuum leaks from thermo valve, system is okay.
- When engine is hot, 185-205°F (85-95°C), and at idle, apply vacuum to hose. If idle does not change and vacuum leaks, system is okay.
- Increase engine speed to 3500 RPM. Apply vacuum to hose. Vacuum should leak until 3.25 in. Hg of vacuum is reached. If this occurs, system is okay.
All Others
- Disconnect Green-striped hose from injection mixer and connect vacuum pump to hose end. When engine is cold, 140°F (60°C) or less, and at idle, apply vacuum to hose. If idle does not change and vacuum leaks from EGR control solenoid valve, system is okay.
- When engine is hot, 185-205°F (85-95°C), and at idle, apply 2.4 in. Hg of vacuum. If idle does not change and vacuum holds, system is okay.
- Apply 6.8 in. Hg of vacuum. If idle becomes unstable or engine stalls (and vacuum holds), system is okay.
VACUUM REGULATOR VALVE
Disconnect White-striped vacuum hose from vacuum regulator valve (Colt) or device box (all other models). Connect vacuum pump and apply 15.7 in. Hg of vacuum. If vacuum leaks with engine off, valve is okay. If vacuum holds with engine at 3500 RPM, valve is okay.
Remove EGR valve and connect a vacuum pump. Plug other nipple(s) if equipped. Apply 19.8 in. Hg of vacuum. Valve should hold. With 2.3 in. Hg of vacuum applied, air should not blow through valve. With 6.8 in. Hg of vacuum applied, air should blow through valve.
Remove Blue-striped and Red-striped vacuum hoses from solenoid valve. Separate harness connector. Connect vacuum pump to solenoid valve where Red-striped hose was connected. With battery voltage applied to solenoid valve, vacuum should leak when applied. With no voltage supplied, vacuum should hold.
Carbureted
- Disconnect White-striped vacuum hose from thermo valve. Connect vacuum pump to nipple "A". (Scheme 10) With engine coolant temperature at 50°F (10°C) or less, vacuum should leak when applied. With engine coolant temperature at 77°F (25°C) or more, vacuum should hold when applied.
- Disconnect all vacuum hoses from thermo valve. Connect vacuum pump to nipples "B", "C" and "D" one at a time. Plug nipples other than one being tested.
- With engine coolant temperature at 104°F (40°C) or less, vacuum should leak when applied. With engine coolant temperature at 176°F (80°C) or more, vacuum should hold when applied.
Fuel Injected
Disconnect vacuum hoses from valve. Connect vacuum pump to valve nipple. (Scheme 10) With engine coolant temperature at 113°F (45°C) or less, vacuum should leak when applied. With engine coolant temperature at 176°F (80°C) or more, vacuum should hold when applied.
