Spark plugs are installed in your engine, and generally changing them out is a simple task. When spark plugs begin to wear out, your engine can misfire, stall and have trouble starting. If you have spark plug problems, look for replacements from popular brands such as NGK, DENSO, Motorcraft, Autolite or ACDelco.
Consider replacing your spark plug wires or boots when changing out your spark plugs.
How long do spark plugs normally last?
Your owner's manual should tell you how often your spark plugs should last. Depending on your model and the type of spark plug, the replacement interval could range anywhere between 30,000 to 120,000 miles.
What causes spark plugs to wear out early?
Each time your spark plug fires, the electrical arc generated wears a tiny amount of metal away from your plug's electrode. Normal use will gradually wear your electrode down to the point where more electricity is needed to trigger a spark, until eventually it can't arc at all. In addition to this wear from normal use, spark plugs can also get worn down by overheating damage, oil contamination, and carbon buildup.
You should replace your spark plugs at the recommended interval for your vehicle.
Rough vibrations and noise when idling
Normally, an idling engine should give off a smooth, continuous sound. When spark plugs aren't firing correctly, your engine can make your car vibrate roughly and sound jittery.
When your spark plugs have problems, your car has to work harder to start, or it may not start at all. Bad spark plugs can also drain your battery, another cause of failure to start. If you're having trouble starting, in addition to your battery and gas, check your spark plugs.
Just as spark plug problems can make it hard to start your car, they can also make your car easier to stall.
When your spark plugs aren't working properly, you may also experience problems accelerating. You may notice a delay between the time you push your pedal down and the time your car accelerates.
When your engine is misfiring, your vehicle will stop briefly before starting again. This can be due to other problems such as a sensor malfunction, but it can also indicate a spark plug problem.
Engine surging (engine hesitation)
A surging engine sucks in excess air during the combustion process, causing your vehicle to jerk and slow or start and stop continually.
Bad spark plugs cause your engine to run less efficiently, with incomplete combustion causing a drop in fuel economy as high as 30 percent. If you're having to refill more often than usual, it could be your spark plugs.
There are several different types of spark plugs:
Copper spark plugs have a solid copper core with a 2.5 mm-diameter nickel alloy electrode. This is the largest diameter of any type of spark plug. The smaller the diameter, the less voltage is needed to create a spark, making copper the least efficient type of spark plug. They are also the softest type of spark plug, making them lose their hard edge and wear out faster. They are best for older vehicles predating the 1980s with low voltage distributor-based ignition systems. They should not be used for high-energy distributor-less ignition systems (DIS) or coil-on-plug (COP) ignition systems, except in specially-designed engines.
Platinum spark plugs are the next grade up from copper. They are harder, and can hold a hard edge for up to 100,000 miles. They are best for cars with electronic distributor-based ignition systems (DIS).
Double platinum spark plugs have a second platinum disc welded to their side electrodes. They are designed for electronic distributor-based ignition systems (DIS). In these systems, the spark jumps from the center to the side electrode on the compression stroke and back to the partner cylinder center on the exhaust stroke. This reverse spark can't be handled by copper or platinum spark plugs.
Iridium spark plugs are the hardest type of spark plug, making them last 25 percent longer than platinum plugs. They also have the smallest diameter at as little as .4 mm, making them the most efficient type of plug. Many cars with COS systems require iridium plugs or iridium plugs combined with platinum plugs.
You should generally use the type of spark plug recommended in your owner's manual. Major spark plug brands include NGK, DENSO, Motorcraft and ACDelco.
Changing your spark plugs is relatively easy if you have some auto repair experience. Check out these step-by-step directions on how to change your spark plugs and how to change your spark plug wires. The process of changing a spark plug basically involves disconnecting your spark plug wire, removing the old plug, inserting a new plug, and reconnecting the wire. It's best to do this one plug at a time to avoid connecting the wrong wire.
Let your engine cool before trying to change your plugs. Be careful not to over-tighten spark plugs when installing them, which can damage their threads and your car's cylinder head. If you're not sure how to replace your plug, it's best to have an experienced professional do it.
If you're experiencing any of the symptoms of a worn spark plug mentioned above, you or your repair professional will need to check your spark plugs, so you'll need to go through the process for removing them even if you don't end up replacing them. When your spark plugs are removed, you may notice any of the following conditions:
Your plugs may look normal, in which case you may want to do some tests to rule out other possible problems, as described below.
Normal with red coating
This results from additives in lower-quality unleaded fuel and does not indicate any problems.
Shiny coating on the tip and side electrode
This indicates fuel fouling, which can stem from a fuel mixture that's too rich, ignition problems, or having your plug's heat range set too low. Check your owner's manual to make sure your spark plugs have a heat range compatible with your engine. If your fuel mixture is too rich, adjust your fuel injection or carburetor.
Blackening on the tip and side electrode
This indicates carbon fouling, which may come from running too much fuel or running too cool with a thermostat stuck open. It may also come from bad wiring, leaking injections or driving too slow for too long a time.
Oil ash fouling
This indicates fouling from engine oil due to worn piston rings or valve guides or seals.
This is a serious condition that will show up as a side electrode that has been burned away. This indicates running too hot due to not enough fuel being present in the mixture or in the combustion chamber. This type of problem can be caused by performance upgrades that alter your engine's recommended plug heat range, such as high-output ignition, coils, exhausts, or cams. Have your fuel injection and timing checked immediately before your plug falls apart, and consider using a spark plug with a lower heat range.
This is another problem that can be caused by performance upgrades. It may also indicate that your engine timing is off, which can be solved by a tune-up. Or it may indicate you need fuel with a higher octane rating. Check your owner's manual to see what octane level you should be using.
This indicates you need to replace your plug.
If you plug looks like it's been beaten by its piston, your piston may be extending too far into the combustion chamber. Have your mechanic investigate.
If your spark plug looks okay when you remove it, it may be worn anyway, or you may have another problem that you can rule out by running some tests. A spark tester will let you confirm that ignition is occurring normally. To use a spark tester, remove your plug and connect it to the long terminal of your tester, using an alligator clip to ground your tester to your engine. Use the electric starter or rewind to crank the engine and look for a spark in the tester. If you see a spark, your ignition is functioning; if not, you have an ignition problem.
Another problem you can test for is spark miss, which can be caused by a plug that has been fouled or that is improperly gapped. To test this, with the spark plug screwed into the cylinder head, attach the spark plug's lead to the spark tester's long terminal and attach the tester's alligator clip to the plug. Run the engine and check whether the sparks are timed evenly. If they're not timed evenly, you have spark miss.
Buy spark plugs online or visit your local Advance Auto Parts store and have one of our knowledgable Team Members help you.
Can I clean my plugs instead of replacing them?
You may be able to clean them. However, since plugs are so cheap, it's generally better just to replace them.
Should I replace my spark plugs earlier than my owner's manual recommends?
Yes, replacing your spark plugs earlier than your manual recommends is a best practice. As your maintenance interval end nears within 20 percent of the recommended time, your gas mileage decreases, making it less expensive to replace your plugs then. Also, if you wait to the last minute to replace your plugs, you run the risk of them seizing to your cylinder's head and making them harder to remove.
Can I use a different type of plug than my owner's manual recommends?
It's generally best to use the type of plug your owner's manual recommends. If you use a different type of plug, upgrading to a better plug (such as upgrading to an iridium plug) will often work, but downgrading to a lower grade of plug will usually cause problems.
How often should I change my spark plug wires?
We recommend replacing your wires whenever you replace your spark plugs. If you want to check their condition, take a look while the engine is running. Cracks or nicks in your wires' insulation or sparks visible along the wire's length when you run your engine are signs of worn wires. You can also check for sparks by checking under your hood with the engine running at night or by spraying the plug wires with a water bottle while the engine is running at night.