To know if your spark plug is firing, you can use a dedicated spark tester, manually ground the plug (carefully) and crank the engine to watch for a blue spark, or use a multimeter to check continuity, with a strong, blue spark (or proper resistance reading) indicating a healthy plug and a weak/yellow/no spark signaling a problem. The most common and safest DIY method involves an ignition tester or grounding the plug to the engine block while someone cranks it, looking for a bright, blue spark in a dark environment.
To run a spark test, first remove a spark plug and reconnect it to its ignition coil. Ground the plug's metal body against the engine block. Crank the engine and observe for a visible spark at the electrode gap. No spark indicates possible faulty ignition coil, bad spark plug, or wiring issues.
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.
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.
Too lean a mixture will result in popping or a misfire; too rich a mix produces sooty smoke and a flame that won't cut.
With an abundance of fuel present, the engine may struggle to burn it efficiently, leading to wasted fuel and higher levels of pollutants in the exhaust. Additionally, a rich mixture can lead to power loss, foul-smelling exhaust emissions, and black smoke from the tailpipe, indicating incomplete combustion.
Pre-ignition can lead to heat building up in the combustion chamber causing the spark plugs to fail. In addition, if the cooling system isn't functioning correctly, it can cause the engine and spark plugs to overheat. This overheating can lead to the spark plug's electrode wearing out faster.
Reinstall the ignition coil and connect the spark tester to the coil and a grounded part of the engine. Start the engine or crank it. Watch the spark tester's gap for a strong, blue spark. If no spark or a weak spark is visible, the ignition coil is likely faulty and needs replacement.
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.
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.
Car running rich symptoms include: Slow acceleration. Strong smell of gas. Low gas mileage.
If an air filter or air induction system is delivering more than the normal amount of air, it will cause the oxygen sensor to detect a lean condition. It will add more fuel and cause the fuel trim to be positive.
The first signs of a blown head gasket often include engine overheating, thick white smoke from the exhaust (sweet smell), milky or frothy engine oil, and bubbles in the coolant reservoir, indicating coolant is leaking into the combustion chamber or oil passages, leading to power loss and rough running. A critical early sign is also unexplained coolant loss with no visible external leaks.
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.
Touch one lead to the end of the spark plug, then touch the other lead to the tip of the black electrode at the other end of the spark plug. An acceptable reading should be between 4,000 and 8,000 Ohms.
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.
Replacing your spark plugs will help ensure your engine runs efficiently, saving you money at the pump. Another benefit of replacing your spark plugs is improved engine performance. With lousy spark plugs, you might experience misfires when they fail to ignite the air-fuel mixture.