You probably already know you need to change your spark plugs, and maybe how to do it. But do you know when to replace them? If you don’t read the signs now, you could be looking at more money spent later. What does a bad spark plug look like, and what does it mean? Here’s how to figure out when spark plugs need changing.
What does a bad spark plug look like?
A “bad” spark plug doesn’t work properly, and the reason for its failure can often be determined through visual clues. What a bad spark plug looks like will depend on what caused it to fail, and they’ll all fail eventually.
A spark plug uses electrical energy from the ignition system to create a spark in the combustion chamber. Whether from a distributor or a coil pack, the ignition energy transfers to the spark plug through the metal terminal on the tip, where it goes to the central electrode.
The exterior ceramic insulator keeps the high voltage from escaping, and the tip of the central electrode creates the spark. The arc of electricity between the central electrode and side electrode kicks off combustion in your engine.
Spark plugs have multiple components, and they all need to work properly. Engine vibrations can damage the insulator over time, cracking the ceramic casing. Excess heat can warp the electrode. Bad gas, too much fuel or air and any other number of conditions can wear out the spark plug prematurely. If any part isn’t working, you will have a failing or bad spark plug.
Signs of a bad spark plug
Short of popping the hood and removing them, you won’t physically know if there’s a bad spark plug. So, how does a bad spark plug look when you are driving? Look out for these symptoms.
Rough idle
If the engine idles rough, it’s a sign the spark plugs might be going bad. This is because the issue causes an interruption in the usual firing order, causing excess vibrations. Note this symptom typically improves some as engine revs climb.
Poor acceleration
Combustion is the reason an engine has power. When the combustion process gets interrupted, so does the power. This makes for faltering, stumbling performance or just a feeling of running on half the cylinders. That last part just might be what is actually happening.
Reduced fuel economy
That poor acceleration does more than annoy you. The decreased performance causes you to step on the accelerator harder to get up to speed. Bad spark plugs can decrease fuel economy by up to 30%.
Backfiring
An engine backfire happens when unburned fuel reaches the hot exhaust components and ignites, causing a loud pop or bang. While the fuel burns, it’s happening at the wrong place and time. Take this seriously because backfires are detrimental to engine performance and health.
Misfires
Similar to backfires, engine misfires happen when the air and fuel mix doesn’t ignite properly, resulting in engine stumbling, poor performance, vibrations, and a check engine light. Spark plugs and other ignition components can cause misfires. Spark plugs are cheap and easy to replace, so if your engine is misfiring, the spark plugs are a good place to start diagnosing.
What to do with a bad spark plug
For cleaning or replacing spark plugs, keep it simple. If the spark plug is dirty, clean it. If the plug is damaged or broken, replace it. Also, remember to have the underlying issue checked out. If the spark plugs were simply old, a simple replacement should do it. However, misfires, oil-soaked or burn damage won’t go away by simply changing plugs.
Nelson Xavier Ssenyange
Team Leader
Germax Autos, Spares & Garage Ltd
Lukade Road, Naalya
0779250886/0752088734
