1978 Models
- Check, clean or replace filter in vacuum modulator (if equipped). Disconnect vacuum hose from EGR port and connect it to intake manifold vacuum source.
- Detach vacuum hose from EGR valve and attach a vacuum gauge to hose. Pinch off hose between carburetor and vacuum control valve (if equipped). With engine cold, start engine.
- With engine cold, vacuum gauge reading should be zero (0) at 2000 RPM. As engine warms up, low vacuum should be indicated. If not, check thermal vacuum switch and vacuum modulator.
- Released pinched hose and check that gauge shows low vacuum at 2000 RPM. This confirms normal operation of vacuum control valve.
- Now pinch off vacuum hose between vacuum control valve and carburetor. Detach vacuum gauge and apply vacuum directly to EGR valve with engine idling. Engine should run rough or stall.
- Reconnect vacuum hoses to proper locations. Released pinched hose. If EGR system tests as described, system is operating properly. If not, check individual EGR components.