You know your spark plug is firing by checking for a strong, blue spark when grounded against the engine block while cranking, which you can do with a specialized tester or by carefully using a screwdriver, but signs of a failing spark plug include rough idling, poor acceleration, check engine light, hard starts, misfires, and decreased fuel efficiency. A weak yellow spark or no spark indicates an issue.
Just like most spark plug problems, cleaning your plugs might fix the issue but if that doesn't do the trick, get them replaced. Routine maintenance can often detect spark plug issues, so be sure to ask your mechanic to check them the next time you go in for an oil change.
Spark plug voltage rise
Because of the spark plug “gap,” coupled with the air/fuel mixture (which acts as an insulator) within the gap, the spark plug cannot immediately fire. As the voltage rise increases to approximately 20,000 volts, the gap within the spark plug can be “breached” and it fires.
If acceleration is taking place with the rev counter on the higher side and the engine in higher gears, a jerk coming from the engine is indicative of a misfiring engine. Similarly, if when an engine is idling, it sounds and feels uneven or rough you are likely to be experiencing a misfire.
Overheating: Overheating can cause the spark plug's electrodes to wear out more quickly. This is often due to issues like incorrect spark plug gap, poor fuel quality, too little fuel available for combustion, or engine overheating.
This section provides a visual representation of how the Spark Plug can look depending on how the engine is running. If the engine is running to lean, the spark plug can look greyish white.
Diagnosing Head Gasket Leak Signs from Spark Plug Condition
If spark plugs don't appear steam cleaned, it doesn't rule out a head gasket leak. A blown head gasket can cause coolant to enter the combustion chamber, leaving deposits or steam-cleaned plugs. Inspect for symptoms like white smoke, overheating, or milky oil.
Spark plug replacement intervals vary from 25,000-30,000 miles for copper plugs to 60,000-100,000 miles or more for platinum and iridium varieties. Symptoms indicating you might need new spark plugs include: reduced acceleration, engine misfires, poor acceleration, and rough idling.
Spark plugs can fail for several reasons, most commonly due to age, wear, and issues with the electrical/ignition system. Abnormal (knocking) combustion, contamination, or overheating can lead to the inability to spark the air-fuel mixture.
Ordinary spark plugs made from copper and nickel should last 30,000 to 50,000 miles but may last as much as twice that many miles. Spark plugs made from platinum and iridium last longer. Platinum spark plugs typically last for 60,000 miles, while iridium spark plugs can last anywhere between 80,000 and 100,000 miles.
An engine misfire often feels like the engine skips a beat. You might feel a rough idle, with the vehicle shaking or vibrating. You might also notice a pause or decrease in power during acceleration. It might seem like your car is stumbling or struggling as you try to accelerate.
A lean running condition may manifest in driveability symptoms that have not (or not yet) triggered a DTC. Customer complaints may include symptoms such as decreased fuel economy, lack of power, hesitation on acceleration, backfiring through the intake, overheating, weird smells or other problems.
WD-40 Multi-use Product is ideal for cleaning spark plugs. Spray WD-40 Multi-use Product on a microfiber cloth and rub over the spark plug. You can even spray WD-40 directly on the spark plug & then wipe it down using a soft, clean cloth.
Depending on the cause of the problem, an issue with a misfiring cylinder can be fairly expensive. For something like a faulty spark plug, repair work should only cost somewhere in the range of $150 to $400. For something more serious, like a blown head gasket, costs can shoot up into the thousands of dollars.
A misfire will cause the engine to momentarily stumble, or lose rpms, and then regain its normal engine speed. The misfire will usually reappear, either under specific operating conditions or randomly. A misfire may occur when your engine is idling, causing a rough or uneven idle.
Your vehicle may begin to misfire when the air filter of its engine is too dirty. Any excess fuel that is not combusted in the vehicle's engine leaves deposits in the engine and on various components of the vehicle.
Have a Misfiring Engine? Learn the Top 5 Possible Causes