Fuel Injectors

Misfire Detection The ECM uses the CKP sensor input to monitor the engine for misfires. As the combustion charge in each cylinder is ignited the crankshaft accelerates, then subsequently decelerates. By monitoring the acceleration/ deceleration pulses of the crankshaft the ECM can detect misfires.

Low fuel level:

When the fuel tank is almost empty there is a risk that air may be drawn into the fuel system, due to fuel 'slosh', causing fuel starvation and misfires. To prevent false misfire faults being logged, the ECM disables misfire detection if it receives a low fuel level message on the CAN bus. Fuel tank content is monitored by the instrument pack, which transmits the low fuel level message if the fuel tank content decreases to less than 15% (8.85 litres; 2.34 US galls).

Rough road disable:

When the vehicle is travelling over a rough road surface the engine crankshaft is subjected to torsional vibrations caused by mechanical feedback from the road surface through the transmission. To prevent misinterpretation of these torsional vibrations as a misfire, the misfire monitor is disabled when a road surface exceeds a roughness limit programmed into the ECM. The roughness of the road is calculated by the ABS modulator, from the four ABS sensor inputs, and transmitted to the ECM on the CAN bus.

Fuel Injectors

A split stream, air assisted fuel injector is installed for each cylinder. The injectors are located in the inlet manifolds and connected to a common fuel rail assembly.

Each injector contains a pintle type needle valve and a solenoid winding. The needle valve is held closed by a return spring. An integral nozzle shroud contains a ported disc, adjacent to the nozzles. 'O' rings seal the injector in the fuel rail and the inlet manifold.

The solenoid winding of each injector receives a 12 volt supply from the ECM relay in the engine compartment fusebox. To inject fuel, the ECM supplies an earth path to the solenoid winding, which energises and opens the needle valve. When the needle valve opens, the two nozzles direct a spray of atomised fuel onto the back of each inlet valve. Air drawn through the shroud and ported disc improves atomisation and directional control of the fuel. The air is supplied from a dedicated port in the intake duct via a plastic tube and tracts formed in the gasket face of the intake manifolds.

Each injector delivers fuel once per engine cycle, during the inlet stroke. The ECM calculates the open time (duty cycle) of the injectors from: l Engine speed. l Mass air flow. l Engine temperature. l Accelerator pedal position (i.e. driver demand).

The fuel in the fuel rail is maintained at a pressure of 3.5 bar (51 lbf/in 2 ) by a pressure regulator incorporated into the pump unit in the fuel tank. An accumulator is attached to the LH fuel rail, to damp out pressure pulses from the pump and ensure that the pressure in the fuel rail is constant. A Schraeder valve is installed in the fuel rail, above the accumulator, to provide a pressure test connection for maintenance.

The nominal resistance of the injector solenoid winding is 13 - 16 Ω at 20

°C (68 °F).