Severity Level: High – Have this checked out immediately
Why does my engine misfire?
Your engine is an orchestra of moving parts, finely tuned and all playing together in perfect time. When one component does not play its part correctly, the whole system can be affected. An engine misfire occurs when one or more parts, perhaps a spark plug or a fuel injector, is not working as it should, and your engine loses power and hesitates. Engine performance is reduced and engine damage is possible.
What is a misfire?
The internal combustion engine found in most cars, trucks, and SUVs on the road today houses a number of cylinders. There are anywhere from four to eight cylinders in most engines. Inside each cylinder is a piston that travels up and down to take part in four operations, or “cycles”. First, a mixture of air and fuel is drawn into the combustion chamber. Second, the air and fuel are compressed before a spark plug ignites the mixture. Third, the resulting combustion drives the piston downward to pedal a crankshaft the way your legs pedal a bicycle. And finally, exhaust gases are expelled through the exhaust system.
An engine misfire occurs when one or more cylinders fails to produce power. The problem could stem from an insufficient spark, lack of compression, or lack of fuel. The result could be likened to your foot slipping off of a pedal while riding your bike.
A likely effect of a misfiring engine includes a drop in fuel economy. But the issue goes beyond fuel loss. Your safety – and the health of your engine – can be at risk as well.
For instance, a sudden loss of power can prevent you from making it safely through an intersection or around a road hazard. Your engine might have a hard time accelerating at all if the misfire is significant. And long term, misfiring cylinders can lead to permanent engine damage.
What causes an engine to misfire?
There are many problems that can cause an engine to misfire. Causes can be related to the ignition system, fuel system, or some mechanical failure in the engine itself.
Among the most common causes of a misfire are:
Ignition Issues
The ignition system ensures that the compressed mixture of air and fuel in each cylinder are ignited to produce combustion. Insufficient combustion can be the result of poor ignition performance from one or more of the following.
- Spark plugs. If a spark plug produces a weak spark – or none at all – the cylinder will not fire and will fail to produce power.
- Ignition coil. The ignition coil supplies power to the spark plugs. If a coil is defective, insufficient electrical current will make it to the spark plug.
- Spark plug wires. On older engines, the coils are connected to the spark plugs with long wires. If these spark plug wires are deteriorated, the electrical current will suffer and result in incomplete combustion.
- Distributor cap and rotor. Modern vehicles feature “distributorless” electronic ignition systems. But older engines rely on a mechanical distributor and rotor to distribute spark to each spark plug. If the cap and rotor are degraded or defective, one or more cylinders can misfire.
Lean Fuel Issues
The ratio of air and fuel that enters the combustion chamber is specific. It is typically controlled by the engine’s computer, the engine control module (ECM). If that ratio is out of balance – too much fuel (rich) or too little fuel (lean), combustion will suffer. When the mixture is lean because of one of the following components, an engine misfire can occur.
- Fuel injector. Fuel injectors are responsible for getting fuel into the combustion chamber. If the injector is defective or plugged, insufficient fuel will be available and the air/fuel mixture will be too lean to produce power.
- Fuel pump. The fuel pump is usually located inside the fuel tank. It forces gasoline to the engine. If the pump is failing, too little fuel will make it into the combustion chambers.
- Fuel filter. Similarly, if a fuel filter (placed in line between the fuel pump and the engine) is plugged, too little fuel will make it to its destination and result in a lean operating condition.
- Intake manifold gasket. If the intake manifold gasket is leaking, the cylinders will pull in too much air, throwing the air/fuel balance off and creating a lean environment.
- EGR valve. Likewise, if the exhaust gas recirculation (EGR) valve is stuck open, too little fuel will enter the cylinders.
- Mass air flow sensor. A failed mass air flow sensor can cause too much air to make its way into the engine as well and cause a lean operating condition.
- Oxygen sensor. One of the roles of an oxygen sensor is to measure the amount of oxygen in the exhaust stream. The ECM uses that data to make adjustments to the air/fuel mixture in the engine. If the sensor is bad, the data will be inaccurate.
Mechanical Issues
- Piston rings. Piston rings seal off the combustion chamber from the rest of the engine. They allow for vacuum and pressure to develop at different stages of the combustion process. If the rings are damaged, an engine misfire can occur.
- Engine valves. Intake and exhaust valves are responsible for allowing air and fuel to enter the combustion chamber and exhaust gases to exit. If a valve is broken, bent, or worn out, a misfire can occur.
- Cylinder walls. Scoring of the piston walls is a problem that, like damaged piston rings, can cause an imbalance that leads to misfire.
- Timing belt/timing chain. The timing belt (or timing chain in some engines) is the conductor that ensures all of the internal instruments in your engine are playing in time with one another. If the belt/chain is off by even one space, ignition timing will be off and a misfire can result.
How do I know if my engine is misfiring?
Just as there are a number of causes of an engine misfire, there are also several signs or symptoms of a misfire.
Signs of misfire
- Loss of engine power
- Vehicle vibrates or jerks during acceleration
- Engine stalling
- Difficulty starting
- Exhaust backfire
- Decreased fuel economy
- Increased vehicle emissions
Can I drive with an engine misfire?
Is an engine misfire serious? Well, it certainly can be. While decreased fuel efficiency and some added emissions might not be an immediate risk, stalling in an intersection is. LIkewise with poor acceleration when you really need to get out of the way or avoid a hazard on the road.
It is technically possible to drive with an engine misfire, but it is really not worth the risk. Depending on the cause of the misfire, your engine could hesitate or stall at any moment, usually when you are idling or trying to accelerate. You should not drive with an engine misfire – unless you are making your way to a trusted repair shop to have the problem diagnosed and repaired.
Can a misfire destroy an engine?
Besides the obvious and significant symptoms that impact your vehicle’s drivability, there are the long term effects on your engine that result from a misfire.
When an engine runs too lean, meaning there is either too much air or not enough fuel, internal engine temperatures spike. Engine knocking can also result. Excessive friction from the problem can cause scoring to the pistons and cylinder walls. Your engine could even seize up altogether if the condition is severe enough.
A misfire will not normally go away on its own. Instead, the damage compounds. And that damage can cost thousands to repair, if it is repairable at all. So yes, a misfire can destroy your engine if you ignore it.
How to fix an engine misfire
Naturally, since there are so many potential causes of an engine misfire, the means of repair will depend on the specific cause. Repairs related to an engine misfire include the following:
- Spark plug replacement
- Spark plug wire replacement
- Ignition coil replacement
- Fuel pump replacement
- Fuel injector replacement
- Fuel filter replacement
- Oxygen sensor replacement
- Cylinder head gasket replacement
- Fuel pressure sensor replacement
Engine Misfire FAQs
Why does my engine misfire?
Your engine can misfire as a result of several problems from a bad spark plug or ignition coil to a faulty fuel pump and more.
What is an engine misfire?
An engine misfire is a condition that occurs when one or more cylinders fails to make power during the combustion process.
What causes an engine to misfire?
An engine can misfire due to problems with the ignition system, fuel system, or mechanical failure.
How do I know if my engine is misfiring?
When an engine misfires, you might feel a jerking sensation or a sudden loss of power. Your engine might backfire or it might stall. Fuel economy typically suffers, and your vehicle might not pass an emissions test.
Can I drive with an engine misfire?
While it is possible to drive with an engine misfire, it is certainly not recommended. Not only can a misfire lead to a sudden and dangerous loss of power, but it can also cause serious internal engine damage.
Can a misfire destroy an engine?
Yes. A misfire due to a lean fuel operating condition can, in the long run, cause significant internal engine damage if left untreated.
