Engine Misfires can be really tough to diagnose if not done properly. In this article, you will find the most common causes of an engine misfire. Engine misfire refers to the situation when on one or more engine cylinder fails to fire causing a drop in power and performance. To understand more about engine misfire, let us first understand some basics of an internal combustion engine.
The most common causes of an engine misfire are bad spark plugs or bad ignition coils in a modern engine, while in older engines there can often be caused by things like the distributor cap or a lean mixture causing the misfire. Always check the ignition first.
|Engine misfiring||Bad spark plugs |
Bad ignition coils
Bad distributor cap
Low fuel pressure
|Rough idle |
Low engine performance
Burned smell from exhaust pipe
|Replace ignition coils |
Replace spark plugs
Replace distributor cap
Repair the low compression
The function of the engine
An internal combustion engine is the main component where the combustion of the fuel and air occur which in turn powers the car. At the core of the engine are the cylinders that contain spark plugs which are responsible for creating a spark in the ignition system enabling the car to run smoothly. If any of the cylinders fails, it results in engine misfire that can potentially damage the engine and cause the powertrain to fail.
Possible Engine misfire Causes
Engine misfire is difficult to diagnose as it causes all sorts of problems including engine idling, loss in acceleration, drop in fuel economy, engine vibration and more. However, in this article, we will highlight some key causes of engine misfire and discuss their solutions.
Damaged Spark Plugs
Spark Plugs are responsible for creating a spark in the combustion chamber which allows the engine to turn on. A damaged spark plug is one of the most common reasons for engine misfiring. It usually gets worn out due to an oil leakage or from carbon buildup. Moreover, excessive engine heat also damages the spark plugs. Thus, it is recommended that the first measure to take when you notice the engine misfire is inspecting the spark plug and replacing them if necessary. Having your spark plugs replaced during an oil change will cost an approximately $100.
Lean Engine Misfire
The lean misfire is also another common reason for engine misfire. The lean misfire occurs when there is an improper mixture of air/fuel ratio and more air is used compared to the fuel. The engine requires more fuel in order to run effectively and with this imbalanced ratio, the vehicle starts to vibrate and a significant drop in performance is observed. There are many reasons why lean misfire could occur, for example, a stuck open EGR Valve, worn out intake manifold gasket, damaged mass airflow sensor, failed fuel pump or a plugged fuel filter. To fix the situation, have your car scanned for trouble codes and replace the component which seems to be damaged.
Damaged Distributor Cap/Ignition Coils
Since there are a number of spark plugs in the engine, each spark plug ignites at its proper time. The distributor is responsible for controlling the timing of each spark to ensure that the combustion process is carried out effectively. A damaged distributor cap can disrupt the sequence of spark resulting in a misfire. The easy solution for this situation is to replace the cracked distributor cap with a new one. Newer vehicles do not use a distributor cap, but it’s a known cause in older cars. In newer cars, the ignition coils are a very common cause of misfires.
Lack of Compression
In the combustion chamber, when the piston is fired, it is pushed down and then pushed back up when more air/fuel mixture is sourced into the combustion chamber. The process of the piston pushing upwards is called compression and if the piston lacks proper compression, there won’t be enough spark created to ignite the fuel/air mixture resulting in a misfire. Lack of compression is usually caused by a blown head gasket or leaking exhaust valve. To figure out if you have a leaky exhaust valve or a blown head gasket, notice if two cylinders next to each other are misfiring. If so, then your car’s head gasket has blown or the exhaust valve is leaking. Moreover, if your car is overheating too quickly and is losing coolant at a considerably faster rate, this indicates that the head gasket is damaged and should be replaced to fix the engine misfire. If you want to find a good compression tester, check this one out on Amazon: OTC 5606 Compression Tester Kit
Damaged Fuel Injector
If you have checked the spark plugs as well as the head gasket and they are fine, it is now time to inspect the fuel injectors. A fuel injector is responsible for spraying the right amount of fuel to the engine. A faulty or damaged fuel injector may not spray enough fuel causing the engine to misfire. Check the fuel injector’s voltage and notice if it is buzzing. A good fuel injector is always buzzing when the engine is running while no buzzing indicates that the fuel injector is dead. If the voltage reading shows zero, then the problem is with wiring or computer malfunction and not the component. The average cost for fuel injector replacement is around $900 to $1500.
A lot of times, people confuse engine misfiring with a “jerky” performance which is usually caused by a damaged transmission and the inability of the transmission system to shift gears properly. To diagnose the problem, check if the misfire is only noticeable at a higher speed. If so, the problem could be with the overdrive gear or a faulty clutch plate. If the engine is missing during acceleration, it may be due to the transmission or the rotors.
Finding the Misfire
If your car’s engine is misfiring constantly, the first step should be to locate and isolate the misfiring cylinder. The traditional technique is to disconnect each spark plug wire one at a time while the engine is idling. If there isn’t any change in the idle speed when disconnecting a certain spark plug wire, then you have found the damaged cylinder. If you want deeper knowledge in how to find a misfire, check our article How to fix misfires.
Power Balance Test
A power balance test provides the same information but uses additional equipment such as an engine analyzer. The power balance test is preferable as it reduces the risk of getting an electric shock due to the high voltage in the ignition system.
Engine misfire is caused by a number of reasons from damaged mechanical components, issues in the fuel delivery system to worn out ignition system. Since the misfire condition can be quite annoying, drivers usually panic and opt for procedures which are expensive such engine overhaul while the problem may be due to just faulty spark plugs. It is recommended to visit an auto specialist in such situation and have engine scanned for trouble codes initially and then decide on other measures.