Diagnosing a misfire
One of the more common malfunctions in a car’s otherwise normal running condition is a misfire. What is a misfire, you ask? A misfire is when the fuel and air in a car’s cylinder doesn’t ignite properly, leading to incomplete or nonexistent combustion in that cylinder. There are several potential causes of a misfire, and it’s often not obvious what the underlying problem is. But, with a little detective work, you can figure out what the problem is.
For combustion, you need a few things – fuel, air, spark, and proper compression. Most misfires are actually caused by simple ignition problems. A worn-out spark plug is one of the most common causes. Spark plugs are cheap and often easily replaced. If you stick to the manufacturer’s recommended replacement interval, chances are you won’t have a problem with them.
If your plugs check out OK, you’re going to want to look at your spark plug wires next, as these are often another cause of ignition-based misfires. A good way to check them is to wait until it’s dark outside, and then pop the hood of your car and mist the spark plug wires with a spray bottle of water while the engine is running. If you see sparks, you know that your ignition wires are worn out and need to be replaced.
Still, there’s a third ignition-based cause of misfires. If your plugs and wires check out, then it’s time to give your coil a check. Because of differences in ignition systems, you may want to check a repair manual for your car for directions on how to test the coil.
If your ignition system is solid, then what should you check next? Logically, the next thing to check is fuel. Your fuel pump is an unlikely culprit for a single-cylinder misfire. Instead, you’re going to want to check individual fuel injectors. In the case of a single-cylinder misfire, you’re going to want to check the fuel injector on the affected cylinder.
If your ignition and fuel systems test as functional, you’re going to want to look at two more things. First, check your car’s timing. If your timing belt has jumped a tooth, it can throw off timing and cause a misfire. Finally, if your timing checks out, you’re going to want to go ahead and do a compression test with the engine wa
Above all, the key to finding the cause of a misfire is to work the problem through methodically. Chances are, if you take that approach, you’ll get to the source of the problem in no time at all.