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Home >> Jeep >> 1981 >> Pickup J20, AWD >> Repair and Diagnosis >> Engine Performance >> Ignition System >> Spark Control Systems >> Testing >> Spark Coolant Temperature Override Switch >> Single-Function for Standard Cooling (4 Cylinder)
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Single-Function for Standard Cooling (4 Cylinder)

Disconnect vacuum hose from distributor vacuum advance mechanism and connect a vacuum gauge to hose. Start engine. With coolant temperature below 120°F, manifold vacuum should register. Disconnect vacuum hose from port "4" of delay valve and cap. Manifold vacuum should not register until coolant temperature reaches 120°F. If valve fails these tests it must be replaced.

NOTE: Ported vacuum is not available with throttle closed. Ported vacuum is available at part throttle (equivalent of 1000 RPM).
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