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Your Ignition coil worn out? » Read more about common malfunctions • Repair • Replacement manual
Reliable combustion with the ignition coil
The ignition coil is a small and inconspicuous component in the engine compartment. Nevertheless it is essential for driving: without ignition coil no combustion is possible and the engine cannot run.
Task of an ignition coil
The ignition coil transforms the 14.4 V voltage of the generator into the ignition voltage. This can be up to 30.000 Volt, depending on car. This high voltage is necessary to generate a powerful ignition spark in the combustion chamber. The ignition coil has a simple technical construction and generally lasts correspondingly long in a car. If it fails, it is easily replaced.
Construction of an ignition coil
An ignition transformer is a voltage-resistant housing with an internal transformer core. The weak 12 V flows from the generator to the coil and is transformed via a copper winding to the required voltage. This is not a lasting effect, but only occurs at the exact moment when the current is needed for the spark plug. The single-part square or cylinder-shaped ignition coil used to be standard. It was used in ignition systems with ignition breaker contacts. This wear-prone ignition system is gradually replaced by contactless ignition systems. This had its effect on the design of ignition transformers. Principally, the comb-shaped ignition coils of contactless ignitions have the same performance as the traditional ignition transformers.
Wear of an ignition coil
An ignition transformer has no moving parts. Common wear therefore does not occur on these modules. They have one important enemy: moisture. An ignition coil is generally insulated with high-resistance plastic, which over time becomes brittle. In view of the strong temperature swings and vibrations in a motor compartment this is unavoidable. Small fissures in the housing allow water to penetrate in the ignition coil. In this case, the component can soon fail.
Identifying defective ignition coils
An old ignition coil can burn through. This defect is very rare. Before this happens, the transformer fails. One of the first symptoms is that the car no longer accelerates properly. This happens as the cylinders no longer receive the required ignition spark. Acceleration becomes irregular and the car stutters during driving. If this occurs, the cause should be found.
A simple way of checking your ignition
Park your car in a dark garage. Open the hood and run the engine. If flashes occur in the engine compartment, a fault current is the cause. Mind the safety: on no account should you touch the damaged parts while the engine is running. The ignition poses no danger when the engine is switched off. If it runs, there is a considerable risk of painful electric shocks! Otherwise, this is a very reliable test. If the flashes emanate from the ignition coil, the culprit is found. In most cases the ignition cables are responsible for fault currents. Therefore it makes sense to replace the entire ignition in case of a defective ignition coil. The cables and spark plugs are very cheap. A full replacement makes your car reliable and durable for many years.
Affordable ignition coils
A new ignition coil is available at ca. 25 EUR (c. £22). High-grade ignition transformers from branded manufacturers like BOSCH or MAGNETI MARELLI cost between 35 and 50 EUR. In combination with fresh spark plugs and cables, the car can start and drive reliably at any time. Tip: Replace or clean all earth cables of the engine. One of them is attached to the battery, one to the generator and the ignition coil is connected to the bodywork as well. On its contact points they often have a layer of rust, causing an insulating effect. Polishing and lubricating these contacts can restore the full ignition capacity.