Are you experiencing a noticeable lack of power when trying to accelerate...almost as if one of your cylinders isn't firing, or if all were just clunking along? Getting lower than average gas mileage? Is your engine stalling for seemingly no reason? There could obviously be many reasons for this condition: fuel delivery, ignition, timing, etc. That means there are lots of tests you must perform to see what exactly is causing this problem. If you have a fuel problem, then you'll likely smell it. Timing issues can usually be solved by checking the TDC marks on the crank and camshaft pulleys. Ignition problems, however, require voltage and resistance tests to pin down. You have to test your spark plug wires your ignition coil(s). Since tens of thousands of volts are required to make a spark, the resistances that you are going to measure in the cables and the ignition coil are also in the thousands of ohms. Always check your vehicle's factory service manual for proper specifications, but if you find your ignition coil is to blame for your misfires then you'll have to replace it ASAP.
Mechanically timed ignition has been around almost as long as automobiles have been, though advancements in technology have certainly changed how components of the system work together to provide an accurately timed spark. Central to all mechanically timed ignition systems is the distributor; however it wouldn't be able to do its job without receiving thousands of volts from the ignition coil. Your spark plugs require somewhere around 50,000 volts delivered at precisely timed intervals. Since your battery is only a 12-volt power source, the ignition coil has to step up the voltage and release it to the distributor as needed. This process happens several million times for each year the vehicle is in operation. So whether you have a central ignition coil powering a distributor or you have an ignition coil on each spark plug, it will eventually fail.
Replacing an ignition coil is usually pretty easy. It involves your car's electrical system, so certain safety precautions must be followed. Always unplug your battery first. The rest of the steps will be different depending on the type of ignition system you have.
Mechanically timed ignition - Single ignition coil