Spark plug replacement
Spark plugs wear at the electrode. As the gap widens the ignition system needs more voltage to jump it, and the burn gets less complete. You lose a little power and a little fuel economy gradually, and the car feels normal because the change happened slowly.
Eventually the coil cannot bridge the gap reliably and you get a misfire — rough running, a flashing check engine light, and unburnt fuel going into the catalytic converter, which is an expensive thing to damage.
Signs the plugs are due
- Rough or uneven idle
- Hesitation when you accelerate
- Harder starting than usual
- Fuel economy that has drifted down
- A misfire code, or a flashing check engine light
- You have passed the interval in your owner’s manual
What replacement involves
- Remove and inspect the old plugs — how they wore tells us about the engine
- Fit the plug type and gap your engine specifies
- Torque to specification, which matters more than people expect
- Inspect coils, boots and wiring while access is open
- Clear any stored misfire codes and road test
The condition of the old plugs is genuinely diagnostic — oil fouling, overheating and a rich mixture each leave a distinct signature, and we will show you if we find one. We tell you what we found and what it costs before we do the work. Nothing happens that you did not agree to.
Frequently asked questions
How often do plugs need changing?
It depends entirely on the plug type and engine — intervals vary widely between makes. Your owner’s manual has the figure for your car.
Is this the same as a tune-up?
Plugs are part of a tune-up, but a tune-up also covers filters, fluids, the ignition system and a diagnostic scan. If you are due for plugs anyway, it is often worth doing the rest at the same time.