Inertia fuel shut-off switch

Inertia fuel shut-off switch

The electrical circuit for the fuel pump incorporates an inertia switch which, in the event of a sudden deceleration, breaks the circuit to the fuel pump preventing fuel being delivered to the engine. The switch is situated behind the centre console and must be reset by pressing the rubber top before the engine can be restarted.

WARNING: ALWAYS check for fuel leaks and the integrity of fuel system connections before resetting the switch.

Diagnostic connector

A diagnostic connector, located behind the ’A’ post lower trim panel in the drivers footwell, allows engine tuning or fault diagnosis to be carried out using TestBook without disconnecting the ECM harness multiplug.

Heated oxygen sensor

The engine management system operates a closed loop emission system to ensure the most efficient level of exhaust gas conversion.

An heated oxygen sensor fitted in the exhaust manifold monitors the exhaust gases. It then supplies a small voltage proportional to exhaust oxygen content to the ECM. As the air/fuel mixture weakens, the exhaust oxygen content increases and so the voltage to the ECM decreases. If the mixture becomes richer so the oxygen content decreases and the voltage increases.

From this signal the ECM can determine the air/fuel mixture being delivered to the engine, and can adjust the duration the injectors are open to maintain the ratio necessary for efficient gas conversion by the catalyst.

The heated oxygen sensor has an integral heating element to ensure an efficient operating temperature is quickly reached from cold. The electrical supply to the heater element is controlled by the ECM via the heated oxygen sensor relay in the relay module.

Acceleration enrichment

When the throttle pedal is depressed, the ECM receives a rising voltage from the throttle position sensor and detects a rise in manifold pressure from the manifold absolute pressure sensor. The ECM provides additional fuel by increasing the normal injector pulse width and also provides a small number of extra additional pulses on rapid throttle openings.

Over-run fuel cut-off

The ECM implements over-run fuel cut-off when the engine speed is above 2000 rev/min with engine at normal operating temperature and the throttle position sensor in the closed position, i.e. the vehicle is ’coasting’ with the throttle pedal released. The ECM indexes the idle air control valve open slightly to increase the air flow through the engine to maintain a constant manifold depression to keep emissions low.

Fuel is progressively reinstated as the throttle position sensor is opened.

Over-speed fuel cut-off

To prevent damage at high engine speeds the ECM will implement fuel cut-off at engine speeds above 7000 rev/min by inhibiting the earth path for the injectors, as engine speed falls to 6990 rev/min, fuel is progressively reinstated.

Ignition switch off

When the ignition is switched off, the ECM will keep the main relay energised for approximately 30 seconds while it drives the idle air control valve to its power down position, ready for the next engine start.