subject: What Makes a Car Misfire? [print this page] What Makes a Car Misfire? What Makes a Car Misfire?
What Makes a Car Misfire?
Information from:http://www.know-car.com/index.php/what-makes-a-car-misfire
Diagnosing the cause of an engine misfire can be a frustrating and daunting task. There are several different reasons why misfires can happen, but fortunately most of them fall under three general categories. Misfires are generally caused by problems with the fuel delivery, the spark or cylinder pressures. However, in each category there are several smaller direct causes that must be investigated to correctly identify the root problem.
Spark
A weak spark cannot properly ignite the fuel and air mixture, causing the mixture to be incompletely burned or not ignited at all. The causes of a weak spark include worn spark plugs, fouled spark plugs, old or worn spark plug wires, worn distributor cap or rotor, weak coil, poor battery cable connections, weak alternator and a weak battery. Fuel Pressure For an engine to run correctly, the fuel pressure must be maintained at a constant minimum level. If the fuel pressure drops below this minimum level, an inadequate amount of fuel will be delivered to the cylinders, resulting in a fuel mixture that is difficult to ignite. Common causes of low fuel pressure are a weak fuel pump, clogged fuel filters, dirty or clogged fuel injectors and clogged or contaminated fuel lines. Low Compression When compression levels in a cylinder become too low, the cylinder is unable to fully compress the fuel and air mixture. Depending upon the reasons for low compression, if it is because of worn piston rings, worn valves or worn cylinder walls, the fuel and air mixture can also escape past these worn components. The end result is the same, with the spark plug unable to properly ignite the fuel and air mixture, and a resulting misfire in the cylinder. Vacuum Leak Vacuum leaks allow too much air to enter into the fuel and air mixture before it is ignited in the combustion chamber. This causes the ratio of fuel mixed with air to be improperly balanced and results in a lean condition where not enough fuel is mixed with the air to encourage proper ignition of the mixture. This causes poor ignition of the mixture and misfiring. Common causes of vacuum leaks are a faulty EGR valve, cracked or worn hoses, worn gaskets and faulty PCV valves. Air Cleaner A clogged air filter will not allow an adequate amount of air to enter the engine. This causes a too-rich condition where there is too much fuel in relation to the amount of air in the fuel and air mixture. The result is fouled spark plugs, reduced spark and poor ignition of the fuel and air mixture leading to misfires.
