Replacing the spark plugs on your 2003 Mazda MPV is not difficult. In fact, it's a rite of passage for the amateur mechanic. The most important thing to avoid is stripping the threads, which will cause major engine damage. The engine is made of aluminum and installing the spark plug at the wrong angle will destroy the threads in the spark plug hole. The threads consist of grooves in the hole that mate with those on the spark plug, except that the threads in the engine are softer and more easily damaged. The MPV has three spark plugs on the front and three spark plugs on the back of the engine.
Twist and pull the spark plug wire from the leftmost spark plug on the front of the engine. Grasp the spark plug wire by the "boot" or the end of the wire that cups the plug. Avoid pulling on the wire itself.
Place the spark plug socket on the spark plug. Turn the wrench counterclockwise to remove the spark plug. Unscrew the plug until it is fully removed from the engine.
Install the new spark plug by carefully placing it in the hole by hand. Turn the spark plug clockwise, but do so only gently by hand. Ensure that the spark plug screws in gently and naturally. Stop turning it at the first sign of major resistance. Check to make sure that you have not stripped the threads. Move on to the next step only when you're sure that you've positioned the plug at the correct angle and have it threaded most of the way in.
Position the spark plug socket over the spark plug and tighten it with the ratchet. Avoid tightening it too much. It will offer increased resistance for about half a turn as the metal washer on the plug is compressed. Once it is good and snug, stop there.
Replace the wire by handling the boot of the spark plug wire. Listen for a "click" that indicates correct installation.
Use this procedure for the remaining two plugs on the front and the three plugs on the back of the engine. Remove and replace one plug at a time, to ensure that you don't mix up the wires.
