Single-Function For Standard Cooling (6-Cylinder & V8 Engine)

Connect a vacuum gauge to center port "D" of CTO switch. When coolant is below 155°F (68°C), manifold vacuum should register. Above 155°F (68°C), carburetor ported vacuum should register. If valve does not meet these requirements, it must be replaced. See Figure .

Fig 1: Jeep Vacuum Spark Control Delay Valve (4-Cylinder Engines) When testing disconnect vacuum hose from port "4".