| Description and Operation Introduction The distributorless ignition system of the 1,4/1,6 litre CVH engines in the Escort '91 comprises a powertrain control module and a number of sensors and actuators. The sensors supply the powertrain control module with input signals which relate to engine operating conditions and this allows the powertrain control module to accurately control spark timing, idle speed (ISC variants) and pulsed secondary air injection (when fitted). Powertrain Control Module There are three different types of powertrain control module used and these are not interchangeable. An ESCP 1 or ESCP 3 module is used on 1,4/1,6 litre CVH engine variants which meet 15.04 emission regulations and an ESC H2 module is used on 1,6 litre CVH engine variants which meet New EEC emission regulations. Crankshaft Position Sensor The crankshaft position sensor is an inductive pulse generator which scans 36‐1 cast protrusions on the flywheel. Minus one means that one of the protrusions is missing. This gap is located at 90° before top dead center and is used by the powertrain control module as a reference mark for crankshaft position. The crankshaft position sensor sends an alternating voltage signal to the powertrain control module which is used to determine engine speed and ignition timing. Intake Air Temperature Sensor The intake air temperature sensor fitted to New EEC emission variants is a temperature dependent resistor which has a negative temperature coefficient, i.e. it's resistance changes inversely with respect to temperature. The intake air temperature sensor is supplied with a reference voltage by the powertrain control module and the resultant voltage signal from the intake air temperature sensor is assigned to a corresponding intake air temperature. Engine Coolant Temperature Sensor The engine coolant temperature sensor is a temperature dependent resistor which has a negative temperature coefficient, i.e. it's resistance changes inversely with respect to temperature. The engine coolant temperature sensor is supplied with a reference voltage by the powertrain control module and the resultant voltage signal from the engine coolant temperature sensor is assigned to a corresponding engine coolant temperature. Manifold Absolute Pressure Sensor The UESC and UPAC powertrain control modules have an integral manifold absolute pressure sensor. The manifold absolute pressure sensor input connection on the powertrain control module is connected via a fuel trap to the inlet manifold. The manifold absolute pressure sensor is an electronic device containing a pressure sensitive component which changes the frequencty of an oscillator. The output frequency is therefore proportional to the applied vacuum. In addition to the sensors described above, ISC variants are fitted with a DC idle speed control motor (which incorporates an idle tracking switch) and a throttle position sensor. Pulsed Secondary Air Injection The pulsed secondary air injection system (when fitted) allows the introduction of fresh air into the exhaust manifold which causes secondary combustion to occur. This secondary combustion reduces the time taken by the catalytic convertor to reach it's operating temperature. | 
