Spirit L6-258 4.2L VIN C 2-bbl (1982)
Fig 38 EGR Valve With Integral Exhaust Back Pressure Sensor
EGR Valve
The EGR valve is mounted on the side of the intake manifold on 4-121 and 6 cylinder engines. On 4-151 engines the EGR valve is located on a
spacer plate located beneath the carburetor. On V8 engines, the EGR valve is mounted on a machined surface at the rear of the intake manifold.
The EGR valve without an exhaust back pressure sensor, Fig. 35, is normally held closed by a spring located above the diaphragm. The valve
opens when enough vacuum is applied through the hoses connecting the coolant temperature override (CTO) switch, Figs. 36 and 37, to the EGR
vacuum port at the carburetor. When vacuum overcomes the spring tension, a pintle within the valve is lifted off its seat and exhaust gas is metered
into the intake manifold.
The EGR valve with an integral exhaust back pressure sensor, Fig. 38, combines the functions of the EGR valve and separate back pressure sensor
into a single unit. This unit is calibrated by the use of selective diaphragm spring loads and flow control orifices. The exhaust gas flow is
controlled by a moveable pintle. When no vacuum is applied to the diaphragm, the pintle is held against its seat by spring tension, confining
exhaust gases to the exhaust manifold. When vacuum is applied to the diaphragm, the pintle is forced from its seat, however, this cannot occur if
the vacuum bleed valve in the power diaphragm is opened.
Exhaust gas back pressure from inside the exhaust manifold flows through the hollow pintle stem into the control diaphragm chamber. If this
pressure is enough to overcome the control spring tension, the control diaphragm moves against its bleed valve. Full vacuum is now applied to the
power diaphragm and the pintle moves, allowing exhaust gas to flow to the intake manifold. If the exhaust back pressure drops enough, the control
diaphragm moves away from the bleed valve and the pintle returns to its seat.
Restrictor Plate
The restrictor plate located between the spacer and the intake manifold can be removed after removing the EGR valve. The stainless steel restrictor
plate is calibrated for a particular engine-exhaust system combination and should never be altered or replaced with one of a different calibration.
