Engine Management Functions

Engine Management System:

Operation

Ignition On
Power is applied to the various devices through contacts FE38-87/30 of the main relay which is energized, via contacts RB4-87/30 of the ignition ON relay, when the vehicle ignition switch is in position II, i.e. when 0 Volts is applied to RB485 of the ignition ON relay.

Application of power to the PCME at FE40-1 and FE40-10 generates a system reset which causes the microprocessor to perform an initialization routine (a software program stored in memory), condition input circuits for sensor scanning and initiates FPM operation to pressurize the fuel rail prior to cranking. The FPM is activated via contacts RS18-87/30 of the FPR which is energized by an output from the HO2S relay at FE44-87/30 itself being energized by the PCME at FE40-7.

On completion of the initialization routine, sensor scanning commences and analogue information from the sensors is converted into digital data for storage. The data thus stored is then evaluated to determine prevailing engine conditions and memory locations are accessed to obtain appropriate ignition timing and fuel metering parameters.

In addition, the following functions are performed:

The stepper motor of the IACV is driven, via FE40-15/16 and FE40-18/19, to set the valve at a position suitable for engine starting. Rapid valve positioning is achieved for all conditions by extending or retracting its stem from a PARK position restored each time the ignition switch is set to OFF.

FPM operation is terminated, i.e. the output at FE40-7 is removed, after approximately 0.5 seconds to eliminate possible fuel flooding should an injector be stuck in the open position. This feature is also used to eliminate possible fuel spillage creating a hazardous condition if fuel line fracture occurs due to impact damage.

The AIRP and AIRV (if fitted) are activated by the AIRR which is energized, via FE40-2, for a time period depending upon engine temperature.

Any DTC codes present from earlier engine operation will be recalled from memory and displayed on the instrument pack fascia.

Engine Cranking
FPM operation is reinstated and any DTC displayed on the instrument pack fascia is erased when the engine is cranked, provided that the PCME detects a CKPS input at FE41-13 and 24. The HO2S heater is also activated to heat the sensor on vehicles fitted with catalyst emission control.

As the engine rotates under the influence of the starter motor, fuel is introduced into the inlet ports by the FI which are actuated by the PCME under control of the CKPS input. Injector triggering occurs, through FE40-13 and 25, three times per crankshaft revolution with appropriate correction factors imposed. The IA is also actuated at the correct times, through FE 40-1, to operate the ignition coil and fire the sparking plugs.


Engine Running
When the engine starts, cranking enrichment is terminated at 500 RPM, water temperature below 42°C. (107°F) or 250 RPM water temperature above 42°C. (107°F) i.e. injector pulses occur once per crankshaft revolution, and both warm-up and after-start enrichment is imposed.

The engine idle speed is controlled, through FE40-15/ 16 and FE4O-181 19, by the PCME which drives the IACV stepper motor from coolant temperature, throttle position and crankshaft speed information. Compensation is also provided for fluctuating engine load by monitoring A/CS and PNPS (automatic only) inputs at FE41-3 and 21 respectively. Engine idle speeds vary with coolant temperature and typically are:

Cold in neutral - 800 RPM. at 20°C.
Cold in drive - 650 RPM.
Hot in neutral - 700 RPM. at 90°C.
Hot in drive - 580 RPM.

Fuel and ignition requirements are calculated at each sensor scanning to maintain optimum engine efficiency over its entire range, including full power and acceleration demands. Should a sensor failure be detected, an output is applied to the instrument pack to provide indication of the failure on the fascia MIL light. The nature of the fault is also stored in PCME memory and is output as a DTC the next time the ignition switch is set to position II.

Exhaust emission regulation is implemented by the PCME under control of the HO2S (if fitted) which monitors the oxygen content of the exhaust gas and provides a corresponding signal to the PCME at FE41-17. This signal imposes corrections on the basic injector ON times to reduce exhaust emissions to a minimum. Power to the HO2S heater is supplied from contact FE44-87 /30 of the HO2S relay to prevent unnecessary current drain.

Additional air is introduced into the exhaust system by a relay actuated AIRP and AIRV (if fitted) to provide a reaction, burning the exhaust gas in the exhaust downpipe and first catalyst. The resulting heat 'lights-up' the first catalyst quickly. The AIRR is actuated by an output from the PCME at FE40-2.

Note: During periods that the AIR is operating, HO2S operation is inhibited.

Fault identification: provided by the PCME in the form of DTC codes.