Misfire Causes and Solutions

Updated on January 8, 2017

What is Misfiring?

What is misfiring and what are the causes of misfiring? In order to understand that, let's talk a little bit first about the internal combustion engine.

The best way to think about an internal combustion engine is to think of a bicycle. Every time a cyclist pushes down on the pedal, the bike gets another small burst of power. It's the same with an internal combustion engine. A bicycle is like a 2-cylinder engine, and every time the cyclist pushes down on the pedal, the bike fires. A misfire occurs when one of the cylinders in an internal combustion engine doesn't fire. Think again of the bike. If a cyclist was only able to use one leg to power the bike, he could still move it and ride it. But it wouldn't have very much power. It's the same with engine misfiring. When a cylinder in an internal combustion engine misfires, the engine can still function, it just doesn't have as much power as it otherwise would. In order for a cylinder to fire properly in an internal combustion engine, it needs 4 factors all working together in concert:

  • Proper Fuel/Air Mixture
  • Proper Compression
  • Proper Timing
  • Correct Spark

Misfire causes are often simple, like a fouled spark plug that can no longer fire.
Misfire causes are often simple, like a fouled spark plug that can no longer fire.

Misfire Causes

If one or more of the above factors aren't in proper working condition, you'll run the risk of misfiring. There are a variety of different misfire causes that can occur that can keep a cylinder from combusting properly. Sometimes it takes a combination of issues in order to make a cylinder misfire. Other times, misfiring isn't consistent, and sometimes the cylinder will fire properly, while other times the cylinder will misfire. It depends on the type of issue and how severe the issues are.

  1. Faulty or Fouled Spark Plugs -- Spark plugs provide the spark for the ignition of the fuel/air mixture in the combustion chamber. But spark plugs can go bad for a number of reasons and are one of the leading causes of misfiring. Spark plugs can get fouled from oil leaking into the combustion chamber, or from carbon buildup. They can also wear down more quickly from overheating and improper gapping. The bottom line is that if you're experiencing misfiring, one of the leading causes is bad spark plugs. It's easy to check and easy to fix. Even if you don't want to do the job yourself, most oil change operations will check and replace your spark plugs for you during an oil change for less than $100. Repairing the cause of your misfiring can save you that much money pretty quick in the boosted fuel economy you'll experience.
  2. Cracked Distributor Cap -- The distributor is what controls the timing of the spark that gets sent in sequence to each of the spark plugs in the engine. This has to do with the timing mentioned in the list above. When the distributor is functioning properly, the spark to each spark plug is sent at just the right time to ignite the fuel/air mixture right when the piston is ready. A cracked or damaged distributor cap can cause the signal to be lost to one or more of the spark plugs, resulting in a misfire.
  3. Lean Fuel/Air Mixture -- The fuel/air mixture is a pretty delicate balance. If the mixture gets out of balance, it can cause a misfire. So what are some ways that the fuel/air mixture can get out of balance? If things like the fuel pump or the fuel injectors get clogged, then not enough fuel will be able to get to the combustion chamber and can readily cause a misfire. This problem can lead to consistent misfiring in all cylinders, and not be restricted to just one.
  4. Lack of Compression -- When the piston fires and is pushed down by the combustion, the piston is then pushed back up again as more fuel/air mixture is brought into the combustion chamber. This upward motion is called compression. If a cylinder lacks proper compression, then the spark from the spark plug won't ignite the fuel/air mixture. Lack of compression can be caused by a variety of things, but mostly by leaky exhaust valve that's been burned, or else a blown head gasket. In either case, you've got a pretty major problem. One way to tell whether your head gasket is causing the problems or a leaky exhaust valve is to see if two cylinders next to each other are misfiring. If so, then you most likely are dealing with a blown head gasket instead of a leaky exhaust valve. In addition to this, if an engine overheats or runs hot, and if you're noticing that you're also mysteriously losing coolant, then you most likely are dealing with a blown head gasket.

Fixing Misfiring

Now that you understand the causes of misfiring, the best thing you can do would be to take your car to your mechanic or local auto parts store and have them hook the car up to a diagnostic machine to read the misfire codes and tell you the nature of your misfire. If your misfire is localized to just one cylinder, it will tell you which cylinder. At that point, you can check your distributor cap to make sure it's intact and check the spark plug in that cylinder. You can also check the compression of that cylinder using the same diagnostic tool to analyze whether or not the exhaust valve in that cylinder is leaking or perhaps whether or not you have a blown head gasket.

If the misfire codes tell you that multiple cylinders are misfiring intermittently, then you can start to surmise that perhaps your fuel/air mixture is too lean and is causing misfiring in different cylinders at different times. If that's the case, then you might want to think about cleaning your fuel injectors with fuel injection cleaner and perhaps changing your fuel pump. If that isn't the problem either and you're experiencing consistent misfiring in all cylinders, at that point, you'll want to take a look at your timing as a whole to make sure that everything is set to fire at the proper times.

Questions & Answers

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      • profile image

        john 

        5 months ago

        piaggio MP3 500cc single cylinder with 2 spark plugs. New plugs were fitted and misfire started. Fires on 1 plug not 2. checked if both spark outside engine, and both sparked on earth contact. Never before did I have this problem. HELP PLEASE

      • profile image

        daniel 

        17 months ago

        I like the way you deal with questions

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