Common Spark Plug Problems and Symptoms

The Spark plugs are the end of the line when it comes to the ignition system. This is where all of the work that went into generating the high voltage pulse from the ignition coil pays off, by exploding the air fuel mixture that has made its way to the combustion chamber.

Three things need to happen for complete combustion to be achieved from an ignition point of view. The first thing is spark hot enough to ignite the air fuel mixture. Second it must be maintained for a length of time long enough to completely ignite the entire charge. Finally it must be delivered to each cylinder at exactly the right moment. Here we will discuss not only the different types of spark plugs but also some of the common problems and symptoms that drivers will experience when something goes wrong.

Discover How Spark Plugs Work

Professional automotive instructors compare the spark from a plug to a bolt of lightning. Naturally, lightning flows through the air between the ground and a cloud with an opposite electrical charge. Mounted in the combustion chamber the spark plug provides the air gap across which the high voltage from the coil causes a similar spark. In a standard plug the center electrode carries the positive voltage from the ignition coil. The ground is provided by the side electrode welded to the threaded shell.

The air gap is between these two points and where the spark jumps across. The amount of space between these positive and negative electrodes is important to performance and plug life. Spaces that are too small can cause premature ignition and incomplete burning of the fuel mixture. Gaps that are too large require an increase demand of voltage to make the jump and will also generate more heat that can actually melt the electrodes.

Different Types of Spark Plugs

Factory and replacement spark plugs are available in three main varieties. The difference between them is the material that the electrodes are made of. With most of the stress and wear occurring at the air gap the quality of materials becomes paramount. The standard used on older vehicles from the 70s and 80s were made with a copper and nickel alloy. Although these are great conductors they are somewhat soft metals and required replacement every 30,000 miles.

Car makers started to install platinum plugs in the 90s and found them superior in performance and longevity but more expensive. The fact they could go for 60,000 miles without service was used as a selling tool. Double platinum spark plugs can go as far as 90,000 miles. Manufacturers figured out the harder the metal used, the longer the plug will last. This brings us to the iridium plug found in many present day automobiles. This super hard metal has a melting point 1200 degrees higher than platinum. These can go well beyond 100,000 miles of service.

Common Problems Associated with Bad Spark Plugs

On cars 1996 and newer sometimes the first sign of trouble is illumination of the check engine light. This can coincide with rough idle, poor fuel economy and performance. OBDII (on-board diagnostics second-generation) monitors the combustion process to verify proper operation. It does this because if a cylinder is not firing, achieving proper tailpipe emissions is impossible due to raw fuel injected into the exhaust post combustion.

In a recent study, one of the top five check engine light codes was a cylinder misfire. These codes can be set for an individual cylinder. As an example if number one is not firing it will set a code P0401 and if number five is malfunctioning, the set code is P0405. Random misfire (PO400) can set if the engine is misfiring on several different cylinders or if the problem is intermittent.

What Bad Plugs look Like

Spark plugs removed from individual cylinders can tell a story all by themselves by the way they look. Ones having a tan to grey colored carbon would be considered normal. If the coloration is whiter, this is an indication of a lean condition where there is more air than fuel in that combustion chamber. In the opposite direction heavy black carbon deposits show a rich mixture where there is more fuel than air.

If you remove one that’s not firing it will be wet and smell like gas. One of the important things when performing a visual inspection is that they should all look similar to each other. Professionals will remove these and lay them out keeping track of what cylinder they’re from. This way they can be compared and problem cylinders identified.

Today’s spark plugs are more efficient and last longer than ones installed in cars of the 80s. However, they shouldn’t be taken for granted as they can be responsible for setting one of the most common check engine light codes for misfire. Although motorists might be tempted to upgrade from copper to platinum or iridium, manufacturer’s and mechanics will recommend sticking with factory installed part numbers.

Engine designers have spent a lot of time picking the right one for the job and are probably more knowledgeable than the parts guy at the local store trying to sell a more expensive version. Maintenance guidelines should be followed closely and are provided in the owner’s manual. On some cars this makes a perfect do-it-yourself auto repair. On other models it can be extremely complicated and best left to the professionals.