I’m sure most of you at some point in your car’s life have had to take your car to a repair facility because the check engine light was flashing and the car was not running as smoothly as normal. When this happens the engine misfiring and the computer is telling you to shut the vehicle off before something is damaged. But what is a misfire exactly? This week we will cover what a misfire is, what causes it and the right way to deal with it if it happens to you.
When one or more of the cylinders are not producing power because there is a lack of detonation in that cylinder, that is known as a misfire. However in order to explain what a misfire is and what causes I will quickly explain how an basic engine works. For an engine to run properly it needs air, fuel, spark and compression. Think of each cylinder as a container. Air and fuel are injected into the cylinder through valves on the top of the engine, the piston moves up to compress the fuel and air mixture which is then ignited by a spark shooting the piston down with a big bang. Voila! You have power. The piston then comes back up to expel the burnt gases out. When you line up multiple cylinders and attach the pistons to one common crankshaft, all these detonations will make enough power to rotate the crankshaft.
Now let’s go over these four main components individually to see how they would inhibit combustion.
When the piston moves down it sucks air into the cylinder which travels from outside of the car through the air filter, into the intake manifold and finally into the engine. The amount of air is measured by an air mass or manifold absolute pressure sensor. If air is restricted (clogged air filter or inlet), unmetered air sneaks past the sensor (vacuum leak), or if the sensors themselves are defective it may cause a misfire.
Without fuel the engine simply will not run. So a fuel pump will only cause a misfire if it supplies enough pressure to start and run the car, but but fails to deliver enough fuel under load. In most cases fuel related misfires are due to a faulty fuel injector.
Compression requires the cylinder to be sealed air tight. After fuel and air are inducted, the piston compresses it into a dense mixture. If the cylinder isn’t airtight in any way after the valves close the mixture will leak out and will not combust. Leaking head gaskets, cracks in the cylinder head or block, worn piston rings etc.
Spark ignites the mixture. If the spark plugs are too worn, or the ignition wires or ignition coils have issues than it will not deliver the spark when it is needed.
Now that you know the basics you’ll have a better idea of what’s going on in your car if ever this should happen to you. But believe it or not misfires can actually be more complicated than this to diagnose. That’s when your friendly certified technicians at MR Auto SD come in handy. One last thing, all these cycles that occur in order for the engine to run have to be synchronized. So in the next installment we will cover engine timing. See you next time!