The spark plugs - here the Bosch spark plug with four earth electrodes - are optimally matched to the Focus engines. With their highly heat-conducting copper-core intermediate electrode and air-gliding spark technology, they guarantee reliable ignition and durability. 1 - Spark plug connector; 2 - ceramic insulator; 3 - spark plug body; 4 - sealing ring; 5 - ground electrode; 6 - thermal cone of the insulator; 7 - intermediate electrode.
In addition, the intermediate electrode and connecting rod are inserted into a conductive glass mass, which ensures the fixing of these parts and the sealing from the combustion chamber side. If the required ignition voltage is achieved, it jumps as an electric spark from the intermediate electrode to the ground electrode. This energy is sufficient to ignite the fresh gas in the combustion chamber.
Different heat ratings
In order for spark plugs to work reliably, they must quickly reach the self-cleaning temperature (around 400°C) after the engine starts. Otherwise, combustion products may be deposited on the thermal cone of the insulator. At full load, the temperature should not exceed approximately 800°C, although the operating mode of spark plugs is not the same in all engines. Only the heat rating decides whether the spark plug and engine are suitable for each other. If you choose a spark plug with too low a heat rating, its thermal cone will heat up too much. This would lead to uncontrolled pre-ignition, which can even destroy the engine. On the contrary, if you use a spark plug with too high a heat rating, it will not reach the required self-cleaning temperature and the thermal cone will become dirty.
The distance between the electrodes increases automatically
In addition to the correct heat rating, spark plugs must have the correct distance between the electrodes. In new spark plugs, this is approximately 1.3 mm, but increases over time: high voltage regularly separates small metal particles from the electrodes. With an increased distance between the electrodes, a higher ignition voltage is required. Consequence: this can lead to misfires, the engine will no longer start reliably.
When replacing spark plugs, be sure to install only spark plugs with the specified heat rating, correct electrode spacing, and correct spark plug threads.
Spark plugs for Focus models:
- 1.4 l Zetec-SE (55 kW/75 hp) — Motorcraft AZFS 22C
- 1.6 l Zetec-SE (74 kW/100 hp) — Motorcraft AZFS 22C
- 1.8 l Zetec-E (85 kW/115 hp) — Motorcraft AYFS 22PP1
- 2.0 l Zetec-E (96 kW/110 hp) — Motorcraft AYFS 22PP1
- 1.8 l Endura Turbodiesel (55 kW/75 hp), DI-Turbodiesel (66 kW/90 hp) — Motorcraft EZD 37