Engine with single overhead camshaft SOHC
Interruption of the circuit of the primary winding of the ignition coil creates a self-induction EMF in the secondary winding of the ignition coil. The high voltage thus generated is fed through the ignition distributor to the corresponding spark plug.
The order of operation of the cylinders: 1–3–4–2.
When a high voltage is applied to the spark plug electrodes, a spark discharge occurs, which ignites the compressed air-fuel mixture in the combustion chamber.
The electronic engine control unit creates and breaks the primary circuit of the ignition coil, thereby adjusting the ignition timing.
Electronic engine control unit using a crankshaft position sensor built into the ignition distributor (Crank Angle Sensor) determines the angular position of the crankshaft and provides the optimal ignition timing depending on the engine operating mode.
When operating a car in high mountains (at high altitude) or driving with a cold engine, the ignition timing advances slightly to ensure optimum engine performance.
Moreover, when knocking occurs, the ignition timing is gradually reduced until knocking stops.
When the automatic transmission shifts gears, the ignition timing is retarded to reduce engine torque, thus eliminating vehicle jolt when shifting gears.
Engine with two overhead camshafts DOHC
This ignition system has two ignition coils with built-in power transistors that supply high voltage to the spark plugs of cylinders 1, 4 and 2, 3, respectively.
Interruption of the primary circuit of the winding of the ignition coil A induces an EMF of self-induction (high voltage) in the secondary winding of coil A. The high voltage thus created is applied to the spark plugs of cylinders 1 and 4. At this moment, sparking occurs simultaneously on the electrodes of both spark plugs (one cylinder is on the compression stroke, the other cylinder is on the exhaust stroke). Accordingly, the ignition of the compressed air-fuel mixture occurs only in the cylinder whose piston is at the end of the compression stroke.
Similarly, when the primary circuit of ignition coil B is interrupted, applying high voltage to the electrodes of the spark plugs of cylinders 2 and 3. The ECM sequentially turns on and off the power transistors built into the ignition coils. Thus, high voltage is applied to the spark plugs of the cylinders in the order 1-3-4-2, the electronic engine control unit, receiving signals from the camshaft position sensor and the crankshaft position sensor, determines which of the power transistors of the ignition coils to apply a control pulse (interrupting the primary circuit of the coil). The electronic unit, receiving a signal from the crankshaft position sensor, determines the angular position of the latter and the optimal ignition timing for a given engine operation mode.
When the engine is cold or driving in high mountains, the ignition timing advances slightly to ensure optimal engine operation. Moreover, when knocking occurs, the ignition timing is gradually reduced until knocking stops.
Attention! When working with the ignition system with the ignition on, care must be taken, as you can get an electric shock from the high-voltage part of the ignition system. People with pacemakers are not recommended to check and repair the ignition system. Switch off the ignition before disconnecting or connecting any element of the ignition system or tester probes.
The main malfunctions of the ignition system are caused by weakening or oxidation of the contacts, short circuit to «mass» high voltage due to contamination, moisture or damage to the insulation of high voltage wires. Before drawing a conclusion about the malfunction of any element in the ignition system, check the condition of the wires or electrical circuits of the ignition system.