1991-Montero-Service-Manual · emission control visual inspection guidelines · страница 6 из 15 · Открыть оригинал PDF ↗
Single Diaphragm EGR Valve
This type uses a single diaphragm connected to the valve by a
shaft. Diaphragm is spring-loaded to keep valve closed in the absence
of vacuum. As throttle valves open and engine speed increases, vacuum
is applied to the EGR vacuum diaphragm, opening the EGR valve. This
vacuum signal comes from a ported vacuum source. Variations in the
vacuum signal control the amount of exhaust gas that is recirculated.
See Fig. 7.
Verify EGR valve is present and not modified or purposely
damaged. Ensure thermal vacuum switches, pressure transducers, speed
switches, etc., (if applicable) are not by-passed or modified. Ensure
vacuum hose(s) to EGR valve is not plugged.
Fig. 7: Typical Single Diaphragm EGR Valve
Courtesy of General Motors Corp.
Dual Diaphragm EGR Valve
This type uses 2 diaphragms with different effective areas
and 2 vacuum sources. Although similar to the single diaphragm type,
the second diaphragm is added below the upper diaphragm and is rigidly
attached to the valve seat. See Fig. 8. These diaphragms form a vacuum
chamber which is connected to manifold vacuum.
During highway cruising when manifold vacuum is high in the
center chamber, manifold vacuum tends to pull the valve closed.
However, the vacuum signal applied to the top side of the upper
diaphragm overcomes the downward spring force and the manifold vacuum
pull, due to the diaphragm’s larger piston. This regulates the amount
of EGR.
When manifold vacuum is low during acceleration, the higher
vacuum signal opens the valve, permitting more EGR. When manifold
vacuum is high during highway cruising, the valve is only partially
opened, reducing the amount of EGR.
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