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Subaru Spark Plugs Questions

A spark plug is a key component in an internal combustion engine which ignites the compressed fuel/air mixture in a piston and provides it with momentum. Spark plugs are linked to the distributor through a pair of electrodes. The distributor is the source of the electrical power which creates the spark.

They are robust elements which rarely fail but when they do, they can be the cause of a host of engine problems. Experts on Subaru cars are often called upon to provide solutions to spark plug problems. Read below some questions Experts have answered and helped provide solutions.

Is it possible for a spark plug wire to come off the plug on a Subaru engine

If the plug wires are fairly old they can work their way loose with engine vibration. This is even more probable if the rubber insulation has hardened and oil seeps into the plug tube. If the plug wires are relatively new and fit well on the plugs they are unlikely to work their way off. A spark plug which has not been properly tightened can also unscrew itself.

Is there an easier way to change the spark plugs on a Subaru Legacy?

The boot which sits on top of the plug is connected to the plug wire. This will somehow have to be cut away or broken off to remove the plug. This means that the plug wire must be replaced. The best way to replace spark plugs is to remove the water reservoir and air filter first to provide more access. Even then it is difficult to reach the plugs and the exhaust might have to be dropped. When this is done the dog bone/motor mount nuts can be removed with the engine raised which will provide easier access.

Another way is to lever the plug wire off the valve cover with a pair of long-handled long nose pliers. When the boot is removed from the wire, the top of the plug can be broken off by tapping it with a small punch and hammer. This should reach the bottom threaded portion of the plug which can then be unscrewed.

How can the plug wires on a Subaru keep working their way off resulting in a misfire?

Sometimes the wires come off the spark plugs even if both are new. The spark plugs on this engine are located in such an awkward position which makes it extremely difficult to reach them. There is no alternative but to wiggle the plug wires till hearing them snap in place which signifies they are properly secured to the plugs. It might be difficult to do this with aftermarket plugs which are a bit short in the boot. This situation will not arise with a factory set which is well worth the additional cost.

A Subaru Outback has been fitted with a second-hand motor but only one spark plug fires. How can one get all spark plugs to fire?

Replace the crank and cam sensors and check that the timing belt is properly aligned. This problem is frequently encountered if the sensors are weak or the timing belt is misaligned.

What can be done to a Subaru WRX which misfires consistently on the first cylinder? The ignition coil and spark plugs are new.

These engines are known for arcing of the spark plug wires within the boot. Remove the spark plug wire from the first cylinder. See if there are white marks inside the boot where it sits on the plug. If white marks are visible then the spark plug wire will have to be replaced.

What are the best spark plugs to install on a Subaru ej20G, and what is the recommended plug gap for peak performance?

The best spark plugs for this car are the NGK PFR7B. The recommended gap is 0.8mm and the torque should be 13-17 lb ft (18-24 Nm).

Spark plugs are a key part of an engine largely responsible for effective performance. It is critical to keep them in perfect working order at all times. Platinum spark plugs, which are the newest innovation, need far less maintenance and offer a lifespan of as much as 100,000 miles. Since engine performance is so closely linked to the way its spark plugs behave, it is always advisable to consult an Expert on spark plug-related issues.
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