A bad spark plug will have a worn down electrode and will also have clack, chunky carbon buildup spanning the gap between the sparking end of the plug and the hook-shaped metal piece overhanging the end.
Dark carbon residue built up on the ends but not spanning the gap of the spark plug and sometimes oily residue on the end (most likely to happen with two-stroke engines that use a gas/oil mixture).
The cost to fix the spark plugs ranges from $80.00 to $150.00 if you have a shop replace the spark plugs.
If you change the spark plugs yourself then it will cost you only the cost of the spark plugs and your time.
You'll need spark plug sockets and the right spark plugs.
Also you should replace the spark plug wires as well because sometimes spark plug wires will tear or be stuck to the spark plugs.
Spark plugs cost between $20.00 to $50.00 per set depending on the vehicle.
Spark Plugs should be replaced every 100,000 miles or so.
Spark plugs are designed for long-term durability, meaning that they only need to be replaced between every 80,000 and 100,000 miles.
However, they can become damaged earlier than expected and require replacements to avoid pricey engine repairs.
Signs and symptoms of bad spark plugs include.
Engine has a rough idle.
If your Spark Plugs are failing your engine will sound rough and jittery when running at idle.
High fuel consumption.
Lack of acceleration.
Also bad spark plugs can cause your engine to misfire. the engine's computer uses sensors to detect these misfires and will create a code that turns on the check engine light.
A flashing check engine light indicates the misfire is severe enough to cause damage to your catalytic converter.