Ignition coils Heated oxygen sensor (HO2S) (Fuel system)

Ignition coils Heated oxygen sensor (HO2S)

The electronic ignition system uses four double ended The oxygen sensors consist of a titanium metal coils. They are mounted on a bracket fitted to the rear sensor surrounded by a gas permeable ceramic of the engine. The circuit to each coil is completed by coating. Oxygen in the exhaust gas diffuses through switching within the ECM, allowing each coil to charge the ceramic coating on the sensor, and reacts with the up and fire. Sparks are produced in two cylinders titanium wire altering the resistance of the wire. From simultaneously, one on compression stroke, the other this resistance change the ECM calculates the on exhaust stroke. Note that coil 1 feeds cylinders 1 amount of oxygen in the exhaust gas. The injected and 6, coil 2 feeds cylinders 5 and 8, coil 3 feeds fuel quantity is then adjusted to achieve the correct cylinders 4 and 7, and coil 4 feeds cylinders 2 and 3. air/fuel ratio, thus reducing the emissions of carbon The resistance of the spark in the compression monoxide (CO), hydrocarbons (HC),and oxides of cylinder is higher than that in the exhaust cylinder. nitrogen (NO_x). Four HO2 sensors are fitted in the Coil failure will result in a lack of ignition, resulting in exhaust front pipe, two each side, and positioned in misfire in the effected cylinders. The fault is indicated front and behind each catalyst. The two rear sensors by illumination of the malfunction indicator light (MIL) are used to monitor the operating efficiey of the on North American specification vehicles. catalysts. Note that if the wiring to these sensors is crossed, the vehicle will start and idle correctly until Injectors the sensors reach operating temperature. Then the ECM will read the signals from them and send one A multiport Sequential Fuel injection (SFI) system is bank of cylinders very rich and the other very weak. used, one injector per cylinder. Each injector consists The engine will misfire, have a rough idle and emit of a small solenoid which is activated by the ECM to black smoke, with possible catalyst damage. allow a metered amount of fuel to pass into the combustion chamber. Due to the pressure in the fuel In the event of sensor failure, the system will default to rail and the shape of the injector orifice, the fuel ’open loop’ and fuelling will be calculated using squirts into the cylinder in a fine spray to aid signals from the remaining ECM inputs. combustion. In the unlikely event of total injector failure or leakage which will cause rich mixture, a A fault is indicated by illumination of the malfunction misfire will occur in the affected cylinder. The fault is indicator light (MIL). ECM diagnostics also use HO2 indicated by illumination of the malfunction indicator sensors to detect catalyst damage, misfire and fuel light (MIL) on North American specification vehicles. system faults.

Idle air control (IAC)

Idle speed is controlled by a stepper motor which consists of two coils. When energised in the correct sequence the coils move a plunger which opens and closes the throttle bypass controlling the quantity of idle air. The stepper motor controls idle speed by moving the plunger a set distance called a step. Fully open is 200 steps and fully closed 0 steps. Failure of the stepper motor will result in low or high idle speed, poor idle, engine stall or non start. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.