DESCRIPTION
The exhaust gas recirculation system is used to reduce oxides of nitrogen (NOx) by recycling some exhaust gas back into the intake manifold to lower combustion chamber temperature.
The EGR system on Turbo models consists of an EGR valve and a vacuum switching valve. The EGR system on other models consists of an EGR valve, a backpressure transducer (which monitors exhaust system pressure), and a thermal vacuum valve which senses coolant temperature.
EGR VALVE
The vacuum diaphragm chamber of the EGR valve is connected to vacuum port in carburetor flange through backpressure transducer and thermal valve on most models.
As throttle valve is opened, vacuum is applied to EGR valve. When vacuum overcomes EGR valve spring force, it opens EGR valve to allow recirculation. On turbo models, manifold vacuum is applied through the vacuum switching valve.
BACKPRESSURE TRANSDUCER
This unit responds to exhaust pressure. Under heavy throttle applications (heavy exhaust pressure), the backpressure transducer closes vacuum passage to EGR valve and regulates EGR action.
Under normal operating conditions, EGR valve functions normally since backpressure transducer allows vacuum passage to atmosphere.
EGR System (Non-Turbo). Scheme 7
THERMAL VACUUM VALVE
Mounted on intake manifold, thermal vacuum valve is connected between vacuum port in carburetor and EGR valve. Valve opens when coolant temperature reaches 122°F (50°C). With valve closed, EGR system does not operate. As coolant warms, valve opens, allowing normal EGR operation.
Turbo Models
The vacuum switching valve prevents the operation of EGR valve until coolant temperature is over 122°F (50°C).
EGR System (Turbo Models). Scheme 8
- Depress diaphragm with finger to verify smooth operation. With engine running, check if engine idling becomes rough when EGR valve is forced open.
- To test EGR valve for leakage, disconnect valve piping at exhaust manifold. Check if engine idling becomes smooth. If valve leakage is observed, replace EGR valve.
Disconnect backpressure transducer hoses. Blow air into Black colored hose on valve. Check that air passes through valve (closed valve) by blowing air into EGR side of valve. Air should travel to opposite side of valve.
Disconnect hoses from opposite side of valve. Blow through hoses connected to valve. Check that no continuity exists between hoses when engine is cold and that valve opens when engine is warmed to 122°F (50°C).
Ensure that engine is cold and that idle and WOT switches are off. Disconnect hoses from opposite side of valve. Blow through hoses connected to valve. Check that no continuity exists between hoses when engine is cold and that valve opens when engine is warmed to 122°F (50°C).