Here is why your car might be misfiring

Thursday November 19 2020
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By David S. Mukooza

If you are having trouble with your car, it may be due to a bad ignition coil. An ignition coil transforms the energy from your car’s battery to a higher voltage to ignite the air-fuel mixture in the cylinder.
Allan Musoke drives a Toyota Spacio and until recently, he had not experienced any major issues. However, nowadays, while idling or at a low-speed, he feels like the engine is shaking and it repeatedly loses power, although he says this normally happens during morning hours or after the engine has not been running for some hours. When he visited his mechanic, he discovered that the ignition coil had issues and needed replacement.

How an ignition coil works
According to Bosco Kigongo, a mechanic, ignition coils are known as compact electrical transformers. He says their purpose is to take volt current normally found in car batteries and convert it into a much higher voltage, which is needed to ignite the fuel and start the engine.
He adds that each spark plug in a car has its own ignition coil. The coil is either physically connected to the spark plug with wires or it sits on top of the spark plug without using wires.
 “If you do not have strong ignition coils, this will result in weak fuel consumption or engine misfires,” he says. 

According to Ronald Lubega, a mechanic, the ignition coil is supposed to last around 100,000 miles or more. He says a jerking motion of the car is a sign of engine misfiring. The causes of misfiring could be faulty spark plugs or wires, bad fuel injector and bad ignition coil. Lubega says when a car is idling or at low-speed, engine shaking or random but repeated loss of power is a result of a faulty ignition coil since the coils are sending irregular electrical currents to the spark plug. 

According to, engine misfiring is when one of the cylinders fires incorrectly or does not fire at all. It can lead to cough-like noises, jerking motions, and vibration while the car is idling at a stop sign or light. These are clear signs of a failed ignition coil. Other causes could be issues with the fuel delivery system and spark plugs. Misfires can occur at any time but are most common at the time the engine is under more load, such as when you accelerate. Also, when a car misfires, it generates more emissions and can ruin other parts, such as the catalytic converter. The sensors get faulty and can change the fuel-to-air mixture, creating even more problems such as the car slowing down instead of accelerating. 

Poor fuel economy
When you have a car for some time, you can determine its average fuel consumption. If you notice less mileage with the same amount of fuel, you could be dealing with a bad ignition coil. When the spark plugs are not receiving enough power, the system compensates by injecting more fuel. 
Another reason for the poor fuel consumption is that when an ignition coil malfunctions, the O2 sensor does an incorrect read and the system sends more fuel than necessary. Also, having bad fuel injectors can cause fuel leaks.

Check engine light on 
Kigongo says if your car’s engine light suddenly turns on, this could be a sign that something is wrong with the ignition coil. An easy way to know what is wrong is to take your car to a mechanic for a check.


Leaking oil states that when an ignition coil is not functioning properly, it can overheat, causing the housing of the wire coils to break, and an oil leak. There could also be a bigger gap in the spark plugs due to erosion. This will cause the ignition coil to operate at a higher voltage and since the ignition is working harder, it can easily overheat.

Replacement cost
Ivan Kaggwa, a spare parts dealer in downtown Kisekka Market, says the cost of a new ignition coil depends on the make and model of the car. ‘‘Some coils are as cheap as Shs80,000, while others will cost as much as Shs150,000,’’ he says, adding that when you suspect that your ignition coils might be faulty, take the car to a mechanic as soon as possible.