What do you do when the spark is missing? Pat Goss has do-it-yourself advice on figuring out what's wrong under the hood when the check engine light goes on, starting with checking out the spark plugs and the ignition coils.

If you're a do-it-yourselfer, you're probably going to learn to hate check engine lights. But you're probably going to have some basic equipment like a scanner. And what you're going to do is a visual inspection under the hood to see if there's anything obviously wrong. Then you're going to hook up your scanner, look at the data stream, and if you don't find anything, you're going to read codes. And in this particular case we have a code P0303. And all the three hundred codes mean misfire. And the last number tells you which cylinder is misfiring. So a P0303 means cylinder 1...2...3 is missing.

Now, today we have an individual coil for each cylinder as opposed to one for all cylinders. So first thing we're going to do is we're going to disconnect the coil, remove its bolt that retains it, take the coil out, then remove the spark plug, and check the spark plug. We're looking for any signs of serious wear or fouling of the spark plug. If the spark plug is bad, then we're going to replace all of the plugs.

Now, one thing to keep in mind is that new plugs often need to be adjusted. And you have to be careful using these conventional tools to adjust spark plugs today because the very fine center electrode on platinum and iridium plugs, well it's easy to damage. So follow the directions.

Alright, so suppose the plugs are good, we still have a problem, what do we do? Well we do what technicians tell you can't be done, we check the ignition coils. And we do that with a simple spark tester for less than ten bucks from the auto parts store. We plug it into the end of the coil where the plug would normally be, we take the ground wire, connect it to a good ground on the engine, and we reconnect the wires that power up the coil. Then, we start the engine. And what we're hoping to see here is a good strong spark, such as we have here. If we have that good strong spark, good. The coil is okay, we have proven that the ignition system is not our problem, now we need to look for a mechanical problem, or a fuel system problem.