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What Are Some Engine Misfire Symptoms?

what causes engine misfire

Engine misfires are one of the most frustrating and hard to understand things for drivers unfamiliar with the inner workings of their engine to deal with. What are the symptoms of an engine misfire, and what does it mean for the health and safety of your car? We’re going to dive into what causes an engine misfire, what the engine misfire symptoms are, and what you need to do if you find that your engine is misfiring.

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What is an Engine Misfire?


The easiest way to understand an engine misfire is to first understand a car engine in general. For our purposes, we don’t need to get too complicated into the fine detail of an engine. Instead, the basics of how an engine operates will set the stage to explain the ways in which it can misfire. There are three things that make a modern combustion engine work in the very simplest terms. You need fuel to burn, oxygen to mix with it, and a spark to ignite it. That’s what happens inside your engine every time you start it and that's why it’s called “turning the ignition.”


You need to ignite the fuel and oxygen mixture in the cylinders which move the pistons up and down. When it works properly, the fuel is injected into the cylinder with oxygen; the spark ignites, creating a small explosion that forces that piston down inside each cylinder in sequence. It happens in each cylinder mere moments apart, over and over, so that it runs quickly and efficiently. That energy is transferred to the wheels through the crankshaft, which propels the car forward. Obviously, a lot more needs to happen around all of that, but these are the basics and also where misfires can happen.


A misfire is what happens when any one of those three components; the fuel, the oxygen, or the spark are not working in the right order or time. The cylinders in your engine are supposed to fire in a precise order and when that goes wrong, it can have a great impact on the overall performance of the car. That doesn't mean your car will necessarily stop working, and if just one cylinder is misfiring the others can and will continue to work as normal, but you will notice a definite slump in the way your engine works. An engine that misfires will have increased emissions and reduced fuel economy, so it’s in your interests to get it fixed as soon as possible.


What Happens When Your Engine Misfires?


Knowing what a misfire is but knowing when it happens is another. There are a number of symptoms that let you know, as a driver, you’re experiencing a misfire. Since your car could potentially keep running even while it misfires, we can break down a few of the more common engine misfire symptoms you should keep your eyes open for. Remember, this is not exclusive to any make or model, so these can be symptoms of a Ford engine misfire as easily as they could be Honda engine misfire symptoms.


  • Rough Idling: This kind of misfire is a good sign that you may have a fuel system misfire. If the car runs fun when you’re driving, but when you’re waiting at a stoplight or when you just start it up, take notice. If it really seems to be struggling as though just sitting still were an effort, that could be a fuel system misfire issue.
  • Rough Acceleration: As you start driving if it feels like the car is jerking but it’s not happening when idling, that’s also a sign of a misfire. Acceleration is putting stress on the engine, so when it seems to struggle to perform that task, you may want to get it looked at.
  • Poor Acceleration: When the air/fuel mix is off as a result of something like a faulty O2 sensor, acceleration suffers. The mix may be too fuel rich or lean and trip your car into something called “limp mode.” In limp mode your engine gets a major downgrade and will only perform under a certain number of RPMs. It’s meant to be a safety feature to get you safely off the road when something is wrong, and drastically limits acceleration.
  • Rough Ride: Your car is supposed to offer a smooth ride for those sitting inside. There are shock absorbers and assorted other pieces of technology meant to make you not feel every bump in the road or growl in the engine. That said, if one cylinder is misfiring, that can unbalance the whole car and noticeably shake up your ride while driving and even idling.
  • Underperformance: Though this is a symptom of many problems, it’s a definite sign of a misfire as well. If one of your spark plugs is off, you could be running with as much as 25% less power under the hood. That will have a very noticeable effect on your performance.
  • Engine Noises: There is often a very noticeable sound that comes from your engine when it misfires. If you’re very familiar with automobile sounds, you'll definitely notice when this happens. The sound can be like a pop, a chuffing, or even a backfire. That backfire sound is what happens when the unburnt fuel gets pushed out during the exhaust stroke and then ignites, exploding out of the exhaust system quite loudly.
  • Engine Stalling: While some misfires will allow you to keep driving with some difficulty, others will result in your engine stalling out entirely. This can happen at idle most often but possibly even while driving which would be especially dangerous. You'll notice this most often when you’re really stressing the engine, such as when you’re waiting at a stoplight with the air conditioning on.
  • Gasoline Smell: There is a good chance that an engine misfire will lead to a distinct odor inside the car. This will usually be the smell of gas but there’s also the potential to notice the smell of burnt coolant which will be a little sweet, and potentially an oil smell as well. This one is harder to pin down as different kinds of misfires can result in different leaks which lead to different smells.
  • Unusual Exhaust: When the misfiring of your engine causes the fuel to not burn properly or not mix properly, you can have a very visual symptom in the form of excessive exhaust fumes. This may also happen when you have leaks causing compression issues that result in coolant or oil getting mixed into the combustion reaction. Your exhaust could be dark black, tinged blue if there’s burning oil, or just unusually thick.
  • Check Engine Light: The last symptom you’ll want to be on the lookout for with engine misfires is the check engine light. Unfortunately, it’s a rather vague indicator of what’s wrong, but it’s also a clear indicator that something is wrong. The “check engine” light will go on and off as your engine misfires. It’s one of the few engine problems that will do this as others cause the light to turn on and stay on. If you watch, this will tell you when you're suffering misfires and help you better diagnose them.  If you’re experiencing any of these symptoms and that check engine light comes on, you know it’s time to go see your mechanic.


What Causes an Engine Misfire?


There are a few ways a misfire can go off in your engine, so let’s explore some of the most common ones.


  • The Spark: If your spark plugs are old, worn, corroded, dirty, or not installed correctly, you may be more prone to misfires. The spark may not happen to ignite the fuel mixture, or it may be sluggish and happen at the wrong time, throwing the precision of the whole engine off. Bad plug wires could also be the cause of the spark not happening at the correct time. Fortunately, both of these are relatively cheap fixes.A bad ignition coil may also be to blame when the spark isn’t working and depending on your vehicle you may have a separate ignition coil for each plug or just one connected to all of them.
  • The Fuel: This doesn't mean you have the wrong gas in your car (although that could definitely be something you should look at), rather that the fuel system is suffering some kind of failure. You may have a faulty fuel filter in this case, or the fuel injection system could be malfunctioning due to being clogged or dirty. When there’s not enough gas in the fuel/air mix they call it a “lean” misfire and it affects all cylinders, not just one like you’d get with a bad spark plug.An intake manifold gasket leak or broken vacuum hose might also be to blame when your engine is misfiring. Additionally, things like a broken fuel pressure regulator or fuel pump can lead to lower fuel pressure which in turn makes the fuel system as a whole fail. As you can see, the issues relating to fuel system misfires can be extensive and wide-reaching.
  • Compression: When you lose compression in your engine, the fuel/air mix is lost before ignition can occur. This is usually caused by a leaky valve or a blown head gasket. Something like a faulty timing belt could also be the reason that compression issues arise.

Because there is such a wide range of potential causes, you may not be able to diagnose this easily on your own. Checking the spark plugs first is often the easiest choice even for those with just a rudimentary understanding of how their engine works and will be the most cost-effective of the causes as well. New spark plugs are very affordable and can be picked up at many stores, even a Wal Mart. If the plugs are not the case, or you're not comfortable buying and replacing them on your own, then going to a mechanic is the best choice. A mechanic can use an OBD2 scanner to help pinpoint the exact cause of the misfire. They can also do a much more thorough check of your valves and gaskets, the fuel injection system, and more to see which part of the entire engine is at fault.


The Cost to Fix a Misfiring Engine


Fixing a misfiring engine can be a mixed bag when it comes to the cost you might face. As we’ve said, a simple spark plug swap could be just a few dollars if you’re OK with doing it yourself. But if you need to go to the shop and get a major replacement of your fuel injection system, you could be looking at hundreds of dollars. From diagnosing the problem to the parts you’ll need to the cost of labor; you could be facing a bill ranging from $300 to well over $1,000. Unfortunately, there's no way to know for sure until you know exactly what's causing the misfire in the first place.


Is it Safe to Drive a Misfiring Car?


You can drive a car that has a continuous misfire but that does not mean you should do it. A misfiring engine is an engine that is constantly being damaged. Your fuel efficiency is going to suffer dearly, which will cost you more money at the gas pump. Additionally, that misfire can cause extensive wear to the engine, the fuel lines, the exhaust and more systems in the vehicle. That wear and tear will degrade performance significantly meaning not only are you paying more money to fuel your car, you'll be driving everywhere more slowly. Couple that with the fact you may be enduring a very rough and wobbly ride and it becomes worse. If there’s a noise issue, that’s another layer of problems to worry about. Add it all up, and there’s no reason to not get the misfire fixed right away.


It’s very possible that, if you leave an engine misfire for a long enough period of time, you could cause irreversible engine damage. That will greatly reduce the life of your car’s engine. Best to fix it as soon as you can now for a low cost rather than wait. The longer it goes, the more expensive it will be.


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