Grand Wagoneer V8-360 5.9L VIN 7 2-bbl (1989)
Spark Control System: Description and Operation
Standard Cooling CTO
The spark control system consists of a vacuum advance mechanism, a reverse delay valve (R/DELAY), a Non-Linear Vacuum Regulator (NLVR), and a
coolant temperature override valve (CTO). Models with the heavy duty cooling system option utilize an additional CTO (HDC CTO). Manifold
vacuum and carburetor ported vacuum are both used to control the ignition spark advance mechanism. A coolant temperature override (CTO) valve
determines the correct vacuum source according to coolant temperature. A non-linear vacuum regulator (NLVR) valve combines manifold vacuum at
idle speed and carburetor ported vacuum at a ratio proportional to the amount of throttle opening. Depending on the coolant temperature, the CTO valve
permits either manifold vacuum or ported vacuum to control the distributer vacuum advance. During cold engine operation the vacuum advance is
controlled by manifold vacuum. After the engine coolant reaches a predetermined temperature the distributor vacuum advance is controlled by ported
vacuum. Ported vacuum is only available when the throttle is opened and engine speed is over approximately 1,000 RPM.
Heavy Duty Cooling CTO
Models with heavy duty cooling systems utilize a single function coolant temperature override (HDC CTO) in addition to the standard CTO to prevent
overheating during high ambient temperature operating conditions. When coolant temperature is below 220° F, ported vacuum is exposed at port 1 and
