1973-75 164 Series
- Disconnect vacuum hose to EGR valve. Connect a vacuum gauge to EGR manifold vacuum port. Start engine. Increase engine speed to about 3000 RPM. Vacuum should be present.
- Connect a hand-held vacuum pump to EGR valve and apply at least 12 in. Hg. Engine should run rough or stall. If engine does not run rough or stall, check for faulty EGR valve or plugged EGR passage. Clean or replace as necessary.
1975-79 All Models With Vacuum Amplifier
Start engine and allow to idle. Disconnect one wire from throttle valve micro switch. EGR valve should open and cause engine to run rough or stall. If engine does not run rough or stall, EGR valve is defective if all other EGR components are okay.
1980-84 All Models
- Ensure engine is at normal operating temperature. Install "T" fitting between vacuum port and EGR valve. Connect vacuum gauge to "T" fitting. Start engine and increase engine RPM. Vacuum should be present and EGR valve should open. Release throttle quickly. EGR valve should close. If vacuum is not present, clean vacuum port at intake manifold.
- Disconnect vacuum hose from EGR valve and plug hose. Apply vacuum to EGR valve. Engine should run rough or stall. If EGR valve functions as described, system is functioning properly.
1975-79 All Models W/O Vacuum Amplifier & 1989-96 All Models
- Ensure all connections are tight and does not leak, vacuum hoses connected and not kinked. Check EGR function with cold and hot engine at different engine RPM.
- With coolant temperature at less than 131°F (55°C), EGR valve should be closed at all engine speeds. If EGR valve is open, replace thermostatic vacuum switch.
- With coolant temperature at greater than 140°F (60°C), EGR valve should only open at partial throttle. If EGR valve remains closed, check thermostatic vacuum switch by disconnecting vacuum hose from EGR valve and blowing air into it. Air should flow freely through thermostatic vacuum switch. If air is not flowing freely, replace thermostatic vacuum switch.
- If EGR valve still will not open or will not close after opening, clean or replace EGR valve.