The perils of cheap ignition coils

Posted on August 5th, 2019 by Rob Marshall

The perils of cheap ignition coils

Ignition coils have been crucial to the petrol engine, even before one was used to power a horseless carriage and are still vital today. Their role is to provide a high voltage spark that is used to jump across a gap on a spark plug, to ignite the petrol and air mixture. Without a decent ignition coil, the spark-ignition engine would not have been feasible. They work hard too – a typical spark plug is fired eight times a second.

 

While older vehicles tended to have a single coil to power all spark plugs, more recent cars have multiple coils and most designs today have a dedicated coil for each spark plug. Over time, the coils degrade and fail, causing a misfire and the illumination of a subsequent engine management light. Continuing to drive the car is not a wise idea, because misfires can introduce petrol into the catalytic converter, which can cause the costly component to overheat and melt internally.

 

Making coils last longer

High electrical resistance is the enemy of ignition coils. Neglecting routine servicing and not replacing spark plugs on time, not attending to oil/water ingress contamination around the ignition system components and not replacing other worn ignition system parts (such as High Tension leads and distributor caps/rotor arms on older cars) increases the voltage demand on the coil. Should a misfire occur, the pent-up energy within the coil is released as heat, reducing its life expectancy.

 

Prioritise quality, not cost

We are coming across low quality replacement coils entering the market, especially online. While low-grade coils cause misfiring and difficult starting, using them can have more serious consequences. As coils are controlled by the engine management computer (ECU) they rely on fly-back voltages that are fed back after the spark plug has been ‘fired.’ Unfortunately, these voltages can be excessively high and ruin the ECU’s ignition drivers and, are therefore damaging, or destructive to the ECU in the process. Therefore, look to buy from brands that either supply the car manufacturer directly, or from a credible parts supplier that supplies OE quality parts – that is, the parts that meet the same specifications as those dictated by the car maker.