Exhaust Gas Recirculation: Testing and Inspection

EGR Valve
1. Operate engine at idle.
2. Disconnect vacuum hose from EGR valve.
3. Apply intake manifold vacuum directly to the EGR valve, the engine should run rough or stall. If engine operates smoothly, replace EGR valve.

Vacuum Amplifier
1. Disconnect vacuum hose from No. 3 water thermo valve and connect a vacuum gauge to the vacuum hose.
2. Operate engine at idle and disconnect vacuum hose from vacuum amplifier. Ensure vacuum gauge reading is approximately 2.0 inch Hg, (50mm Hg).
3. Connect vacuum hose and increase engine speed gradually to 3500 RPM. Ensure vacuum gauge reading is approximately 3.54 inch Hg, (90mmg). If vacuum readings are not to specification, replace vacuum amplifier.

Water Thermo Valve

GLC Models
1. Disconnect vacuum hose from vacuum amplifier and hose from No.1 purge control valve.
2. Operate engine at 2000 RPM. Position a finger over disconnected hoses to ensure no vacuum.
3. Operate engine until coolant temperature is 132° F, (55° C) and check for vacuum. If no vacuum, replace No. 3 water thermo valve.

626 Models
1. Disconnect vacuum hose from water thermo valve.
2. Start engine and operate at 1500 RPM.
3. Position a finger over each disconnected hose and check for no vacuum.
4. Operate engine until coolant temperature is 84-161° F, (46-54° C) and repeat step 3. If there is vacuum, replace water thermo valve.

Water Thermo Switch

1. Remove water thermo switch.
2. Place switch in container of water and connect circuit tester to terminals of switch, then slowly heat water while observing temperature.
3. Tester should show continuity when water temperature is above 59---67°F.