EGR Functional Tests

EXC. 4-156 ENGINE

Ambient temperature in the area of the vehicle must be above 68 degrees F. for this test.
Warm up engine and allow the engine to idle in neutral with the carburetor throttle closed. Abruptly accelerate the engine to approximately 2000 RPM, but not over 3000 RPM. Visible movement of the EGR valve stem should occur during this operation; this can be determined by change in the relative position of the groove on the EGR valve stem. This operation should be repeated several times to confirm movement. Movement of the stem indicates that the control system is functioning correctly.
On 1983 6 cylinder and V8 models and 1984-87 rear wheel drive van models, if control system is functioning properly, check the passage in the valve and manifold for proper flow. Disconnect EGR hose to the CTS or CVSCC valve at the CTS or CVSCC valve end. Disconnect air cleaner to carburetor hose at the carburetor end. With the engine idling, hold the free end of the EGR control valve hose tightly against the opening of the carburetor connector where the air cleaner hose was removed. With hose held against connector, engine should stall, or idle speed should drop by approximately 150 RPM. This reduction in idle speed confirms that exhaust gas recirculation is taking place. If idle speed does not change, or drops less than 150 RPM, exhaust deposits in the EGR valve or intake manifold EGR passage are indicated.
On 1984-87 Pickup, Ramcharger, 1987 Dakota and 1987 front wheel drive van models with fuel injected 4-153 and V6-181 engines, if control system is functioning properly, check the passage in the valve and manifold for proper flow. Connect tachometer to engine, then disconnect vacuum hose from EGR valve and connect suitable hand vacuum pump to valve. Start engine and slowly apply vacuum to valve. As vacuum reaches 3-5 inches Hg, engine speed should drop, and continue to drop as more vacuum is applied. If engine speed does not drop, a defective EGR valve or plugged intake manifold EGR passage is indicated.
On Rampage, Scamp and front wheel drive van models equipped with 4-135 engine, if control system is functioning properly, check the passage in the valve and manifold for proper flow. Disconnect vacuum hose from EGR valve, then connect an external vacuum source of 10 inches or more to valve diaphragm and observe valve movement. If valve does not move, it is defective and must be replaced. If valve opens approximately 1/8 inch, clamp off supply hose to check for diaphragm leakage. If valve does not remain open for at least 30 seconds, replace valve.