Remember to ask your mechanic to check the spark plug gap before installing the new plug.

THERE was a time when spark plugs were regularly replaced at every service. It was easy to sense when replacement was necessary as the car would be difficult to start and run badly. They don’t make them like they used to, thank God for that. Nowadays, spark plugs are a commonly skipped item on the maintenance chart. Due to the advent of fuel injection and better quality spark plugs, some owners tend to ignore them as the car seems to run well enough. But this practice is actually quite bad for the car, not to mention your wallet.

Most new cars nowadays have sophisticated fuel injection systems. The multiple sensors are able to compensate for quite wide variations in running conditions and vehicle conditions. This compensation is able to extend various items to the maximum life and sometimes beyond. A typical driver would not be able to detect any variation in performance due to the slow degradation of the components and also the aforementioned compensation.

Typically, spark plugs require replacement around the 50,000km mark. Sometimes, the spark plug may also be one of the sensors that the ECU relies upon for information. Degradation in the condition of the spark plug and the subsequent compensation may be putting a larger dent in your wallet. Some vehicles require special plugs and also a designated spark plug cap. These are signs that the plugs may perform specific roles, other than merely providing a spark. Check your owners’ manual for the proper spark plug for your car and do not replace it with a different type in any circumstance.

In any case, if you encounter any of these symptoms, your spark plugs may be due for replacement.

Slow(er) Acceleration

The materials used to make a spark plug are quite hardy, due to the harsh environment they function in. But these materials gradually wear down and can significantly reduce your car’s ability to accelerate. It can be hard to detect, especially if you do a lot of town driving, but an occasional acceleration test is a good idea. If you are familiar with how hard your car accelerates, you will be able to detect any sluggishness or slow-down in its rate. Of course, there are other items that may also affect acceleration, such as clogged injectors, clogged fuel filters, faulty oxygen sensors or other things. Have your foreman check the various systems and you may find that replacing the spark plug cures the problem.

SPoor Fuel Economy

A new spark plug will create a large spark that burns fuel efficiently. Once it starts wearing out, the spark may become less bright and burn less fuel. To compensate for the lack of spark, the ECU compensates by increasing the rate the car consumes fuel in order to meet your demands. You may not detect this at all unless you monitor fuel consumption regularly. If you feel your car is consuming more fuel than normal, but is running fairly well, it may be because of the deterioration of your spark plugs. Remember to ask your mechanic to check the spark plug gap before installing the new plug.


Misfiring is a definite symptom of something amiss in your ignition system, be it the ECU, spark plug cables or the spark plugs themselves. Sometimes, it may be a sensor malfunction as well, but this may be detected through the “engine check” light. A misfire is a stumbling or spluttering sound from the engine and requires immediate attention. Failure to correct the situation will cause excessive emissions, decrease in power and increase in fuel consumption.

Difficulty Starting

The Car

Worn spark plugs will cause difficulty in starting. However, since the whole ignition system is responsible, there may be other causes as well. A good indicator is the time needed to start the car; if it takes more than 2 seconds for the engine to start (but otherwise runs normally), it may be an indicator of worn out spark plugs.

The little ceramic and metal things we call spark plugs were usually easily accessible back in the day, and for good reason, as they needed regular replacement. Nowadays, opening the bonnet confronts us with a large plastic cover and multiple other items obscuring the spark plugs. No wonder that sometimes these hardworking items are ignored by DIYers and lazy mechanics. So get to know how to replace your own spark plugs (YouTube is a nice place to start). Beware the dreaded cross-threading (look it up), and pick up those tools. See you under those plastic covers soon!

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