I suspected my coil was bad on my 2003 Ford Focus and decided to figure out exactly how to test it. Unfortunately it was not completely clear so I had to aggregate multiple sources. Here is a (hopefully) coherent version:- Take it out
- Measure the primary and secondary resistances according to this picture. If something is infinite, the coil may be broken. Be careful though, make sure you are testing it right and getting a solid connection.
My car just needed new plugs & wires. I wanted to be sure that was the problem before I just replaced them willy-nilly though!
Check out this thread for more info: http://www.focusfanatics.com/forum/showthread.php?t=180606
