Spark Plug Faults: How to Define the Problem

Of all the many components of a car, spark plugs are probably the simplest. There are only three parts – a steel body, an electrode, and a porcelain insulator between them. At first glance, the task of the spark plugs is simple – to transmit a spark to the working chamber to ignite the fuel mixture in the cylinder. For over a century, they have been doing this, but not always as good as they should. The Indy Auto Man technicians explain why spark plugs may fail and how to define the issue before serious damage.

Experts also note that today, it is customary to change spark plugs preventively without waiting for failure. The reason for this approach is that a spark plug failure, for example, in a powerful turbo engine, can result in loss of traction and even total breakdown.

So, the symptoms of non-working spark plugs are as follows.

Difficulty in starting a cold engine and uneven operation

While drivers still argue whether it is worth warming up the engine before driving, it is a way to reveal the problem. In the morning, when you start a cold engine, you notice that it doesn’t start right away, and once it starts, it runs unevenly—stalls or doesn’t maintain a constant speed. The problem disappears as soon as it warms up. With such symptoms, a faulty spark plug is a quite likely option – the soot may cover it due to engine wear, or its service life is ending, but, one way or another, the spark plug needs to be replaced.

Check Engine light

Any indicator on the dashboard always requires increased attention. The Check engine sign does not always mean a faulty spark plug. Much more often, this indicates an issue with an oxygen sensor or a clogged catalyst, but the condition of the spark plugs is the first thing the diagnostician will look at. One is likely to be guilty of omissions and needs replacement.

Periodic interruptions in the operation

The engine runs smoothly at idle and shudders periodically when accelerating. At this moment, the tachometer needle briefly jerks down, and this symptom is even more pronounced when moving uphill. It is hard to identify the issue at an early stage as, in general, the engine operates normally. It accelerates well and does not consume more gasoline than it should. But over time, a spark plug that begins to fail under heavy load will increasingly spoil the picture of ideal fuel combustion in other modes, and the driver will feel a constant lack of traction. In the end, the spark plug will fail, and the engine will begin to shudder noticeably, even at idle. By the way, an old and proven way to bring a faulty spark plug back to life for a while is to let the engine run idle.

In four-cylinder engines, tripping is easy to recognize – the power unit vibrates, and if you open the hood, you can see that the engine is shaking in time with the idle cylinder, and a noticeable rumble replaces the steady hum from the exhaust pipe. Nonetheless, the increase in power output may go unnoticed in engines equipped with six cylinders, and it becomes even more indiscernible in engines boasting eight cylinders. The exhaust will help in this case, as down there, at the edge of the exhaust pipe, you will hear periodic popping noises – also in time with a non-working spark plug.

What is the service life of modern spark plugs?

It’s a paradox, but the mileage of spark plugs can be three to six thousand miles or sixty, and more. It all depends on the degree of engine boost, the amount of high voltage, the gasoline used, and the quality of the spark plugs themselves. Therefore, when purchasing spark plugs, you should not save too much. They are not easy to change on every car, and in some multi-cylinder engines, spark plugs are replaced only after dismantling the power unit. Preventive replacement of working spark plugs during major maintenance, in this case, is not a whim of service workers but a norm prescribed by the factory.

For the rest of the models, the experts advise listening to the engine at least occasionally and thinking about replacing the spark plugs at the first sign of tripping.