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 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.
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.
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 115-129°F (46-54°C). With valve closed, EGR system does not operate. As coolant warms, valve opens, allowing normal EGR operation.
- Disconnect vacuum hose from EGR valve and connect outside vacuum source, such as hand pump with gauge. Apply about 4 in. Hg and hold this level. Vacuum should not leak down.
- While applying vacuum, watch movement of valve stem. At 4.7 in. Hg (Fed. Man. Trans.) or 3.9 in. Hg (all others), stem should move diaphragm to full up position. If valve does not respond as indicated, replace EGR valve.
Apply a pressure above 0.07 psi (0.005 kg/cm 2 ) to port connected to backpressure signal pipe and check transducer for leaks. If leaks are noted, replace transducer as an assembly.
Remove thermal vacuum valve from engine and place sensing portion in water. Water should be at 115-129°F (46-54°C) for automatic transmission equipped vehicles or 113-131°F (45-55°C) for manual transmission equipped vehicles. Blow through hoses connected to valve. Air should pass, indicating valve is open. If not, replace valve.