Variable Cam Timing System: Notes

Variable Cam Timing (VCT) system applies only to 2.0L ZETEC (VIN 3) engines on Escort and Focus models. VCT system consists of control solenoid, five-tooth pulse ring (4+1) on exhaust camshaft, Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor, Camshaft Position (CMP) sensor, Mass Airflow (MAF) sensor, Crankshaft Position (CKP) sensor and Powertrain Control Module (PCM).

VCT system allows the exhaust cam to advance and retard at varying engine speeds. This is to reduce exhaust emissions and increase fuel economy. As exhaust cam retards, residual exhaust gases are left in combustion chamber. Residual gases cool combustion chamber and are inert when mixed with incoming fresh charge of fuel and air. This results in better fuel economy and lower Nitrogen Oxides (NOx) and Hydrocarbons (HC) emitted from the engine. VCT system eliminates the need for an Exhaust Gas Recalculation System (EGR) system.

VCT system is enabled by PCM when proper operating conditions are met. PCM disables VCT system if a fault is detected. PCM continually calculates a cam position error value based on the difference between the desired and actual position and a duty cycle is commanded for VCT solenoid valve. During closed loop, PCM outputs a revised duty cycle to VCT solenoid valve to correct for cam position error.