You should replace the spark plugs periodically because the sparking performed by the plugs wears away at the face which the spark is formed on. This causes the "spark plug gap" to become incorrect and cause poor performance or running. Also, if there is a problem with the fuel mixture, it is possible for the spark surface to become coated in oil or fuel which can result in incomplete sparking, again affecting running and performance.
You should replace the spark plugs when your car won't start first time but does eventually.
Replace them every 100,000 miles.
most spark plugs should be checked and gapped annually. if your spark plugs are used up you should replace them
Your spark plug manufacturer would recommend your replacement schedule.
Every year, or as an when the service requires
To replace the spark plugs on your Celebrity requires a 5/8" spark plug socket, short extension and either a ratchet or breaker bar. First remove the spark plug wire then use the socket to remove the spark plug. The spark plugs should have a .045" gap. Replace the spark plug and reattach the wire. Continue until you have replace all of the spark plugs.
The Champion spark plug rj19lmc should be able to replace j19lm. Many of Champions spark plugs are interchangeable with plugs with the same letter coding.
Generally, to replace spark plugs on a Subaru vehicle, the spark plug boot should be removed. Then, the old spark plugs should be removed using a socket wrench, and replaced with new ones.
How do you replace the spark plugs on a Peugeot 307?
How to replace spark plugs in a 1989 jeep cherokee?
Yes, you should replace the spark plugs in your Forester at the intervals recommended in your owner's manual.
This will dpend on the type of vehicle you have,as engines do vary. Generally speaking a socket wrench should work for changing your spark plugs.