An engine misfire is quite a common problem. It’s a term referring to a cylinder that isn’t “firing” – one that isn’t setting the air/fuel mixture within it alight. Therefore, it isn’t contributing to the overall power output.
In this article, we’ll be exploring what a misfire is and some of the first things you should be checking.
There are many possible causes of misfires, making it potentially difficult for beginners to find their way around. That being said, it’s by no means impossible, and you could use this article as the first step if you so wished to.
I hope you find some answers in this article.
- How Engines Work
- What Is An Engine Misfire?
- Symptoms Of An Engine Misfire
- Causes Of An Engine Misfire
- Common Misfire Questions
- Reduced Engine Power – What’s Causing It And How To Fix It
- P0300 – Random/Multiple Cylinder Misfires Detected – Audi R8
- Car Dies While Driving – Common Causes And How To Diagnose
How Does An Engine Work?
Before looking in more detail into what an engine misfire is, let’s consider how an engine works.
If this topic is something you’re already all too familiar with, feel free to keep on scrolling to the following sections.
A car’s internal combustion engine (often abbreviated to “ICE”) generally works in a “4-stroke” pattern, colloquially known as “suck, squeeze, bang, blow”. In technical terms, we’d say “intake, compression, power, exhaust”.
An engine typically consists of several major components, including (but not limited to) the crankshaft, con-rods, pistons, piston rings, cylinder block, camshaft or camshafts, valves, and spark plugs.
When an engine works properly, all of these components work in harmony to produce the power needed to drive your wheels forward.
A Brief Guide To How An Engine Works
The video I’ve selected here comes from Autotechlabs on YouTube. The narration is robotic, but the animation is incredibly useful for visualizing how an engine works.
As mentioned, there are four stages – or “strokes” – involved in one revolution (“rev”) of an engine. These are the intake, compression, power, and exhaust strokes.
During the intake phase, the piston travels downwards within the cylinder. As it does so, it pulls a mixture of air and fuel through the intake valve into the space it left behind. Sometimes, manufacturers design engines with air and fuel mixing before going into the cylinder; however, should you drive a direct injection engine, the fuel is sent straight into the cylinder. Only there it mixes with the air.
The piston then reaches BDC (“bottom dead center”). At this phase (for the purposes of a brief introduction, at least), the intake stroke is complete.
It then begins traveling upwards again, representing the start of the next stroke: compression. As the piston travels up, it squeezes the air/fuel mixture together into a tiny space between TDC (“top dead center”) and the top of the cylinder.
The spark plug “fires” – that is, creates a spark – just before the piston reaches TDC again. The air/fuel mixture is highly flammable and should easily combust within the cylinder (hence “internal combustion” engine). A powerful spark, such as what spark plugs produce, should be more than sufficient for doing this.
The force of this contained explosion forces the piston back downwards again. It is from this stroke – the power stroke – that the engine gets all of its output. As the explosion forces the piston down, it causes the crankshaft to rotate due to connecting rods (“con-rods”). In turn, the crankshaft powers everything from your wheels to your alternator to your air conditioning.
So the piston travels back down under the explosion’s force, eventually reaching BDC again. This signals the commencement of the exhaust stroke. As the piston rises again, the exhaust valve opens. The piston pushes all the burnt gases out of the valve. From here, they travel down the exhaust pipe and get expelled into the atmosphere.
After that, the exhaust valve closes, and the whole process starts all over again.
What Is A Misfire In An Engine?
Engine misfires happen when one or more of the cylinders aren’t “firing” – a “misfire”.
There are many – many – possible reasons for an engine misfire. Perhaps too many to count. However, on this page, I’ll try to go through some of the most common causes and things to watch out for.
If you’re experiencing an engine misfire, the key to solving it is logical thinking. It sounds a bit silly to say, I know, but it works.
Go through the process of how an engine works over and over again. Articles, books, magazines, and YouTube videos are all useful sources of information on this front.
Somewhere in that process, something isn’t working correctly. That’s perhaps the most basic definition of a misfire. Once you’ve found that fault and repaired it, you should have solved your misfire.
In the next section of this article, we’ll walk through a few possible causes of engine misfires. As usual, this list is far from exhaustive. If none of the below are your cause, you may need a rethink. Don’t be afraid to bring in a friend or call a mechanic if you need to – that is, after all, what they’re there for.
What Are Some Symptoms Of A Misfire?
The most obvious symptom of an engine misfire is a drop in power. You’ll notice it, without a doubt. It’s not just a slight drop – it’s pretty significant.
When you press the accelerator pedal to speed up, you’ll notice that not much happens. The top speed might reduce significantly, too.
A misfire can cause all of this because it ultimately means that one or more of the cylinders isn’t contributing to the engine’s power output. It’s actually putting drag on the system and so slowing it down even further.
Some other symptoms include the following.
- The engine will sound different – popping sounds, or similar, are often reported.
- Both the engine and the transmission will shake – this stems from the engine being unbalanced. Since the transmission is bolted onto the end of the engine, it also shakes. You can usually feel this through the gear selector, through your seat, and by opening the hood.
- It might struggle to start or maintain its tick-over speed.
- You might see an increase in fuel consumption and emissions output.
When you have an engine misfire, you’ll likely notice most or all of these symptoms rather than just one or two.
Engine Misfire Causes
As mentioned, a misfire simply means there’s no power coming from a cylinder. The “power” stroke isn’t happening due to a lack of explodingment (not the technical term).
You can have multiple misfires at once, easily – for example, if there was damage to the camshaft.
It’s even possible to have all your cylinders misfiring at the same time. In this case, your engine will crank (due to the starter motor) but not start (turn over) or run.
In the following examples, let’s use the standard ignition coil-based Inline-4 engine instead of one utilizing a distributor. That is an engine with four cylinders in a straight line, connected with a crankshaft at the base. This engine is probably the easiest to visualize for a beginner.
Ignition System – Engine Misfire Causes
The ignition system isn’t just the key when you turn the engine on. The word itself refers to the “igniting” of the air/fuel mixture within the cylinders. When you “turn on the ignition”, you are starting up the electrical systems of the car in preparation for when you turn the key to “START”. You’ll notice that once you let go of the key, it clicks back to the “ON” or “IGNITION” position.
The electrical system in a car is also responsible for sending a charge through the spark plugs, causing them to, well, spark. Clearly, the ignition system must be on before the car can start. That’s why the ignition system is one of the steps in the key-turning process.
The ignition system is primarily electrical, and thus the issue may be electrical in nature. In modern cars, electrical pulses get sent to each spark plug through an ignition coil.
If you decide to work on your own car, beware – spark plugs fire on at least 12,000 Volts. Sometimes it’s up to 40,000 V. While the current is low and thus the danger is reduced, this amount of energy is still enough to give you a nasty shock and could be fatal for some people. Always be extremely careful when working on electrical systems.
Old Spark Plugs
Old or dirty spark plugs are probably the number one cause of engine misfires. I don’t have any statistical evidence or analysis to back that fact up, just experience of working with this situation.
Many times, a new set of spark plugs will breathe new life into your engine.
Over time, carbon can build up on the spark plugs. This is quite inevitable, really, although newer cars are much better at minimizing the amount.
If the air/fuel mixture is rich – that is, if there’s more fuel than the average recommended ratio – then the spark plug might not burn all the fuel. As a result, you end up with some hydrocarbons just floating around in there.
These hydrocarbons commonly build up on the firing end of the spark plug. From this, you end up with spark plugs that can’t spark. So just “plugs”, I guess.
If they can’t spark, they won’t ignite the fuel, so the power stroke won’t happen. This is a misfire.
To fix it, replace your spark plugs. Spark plugs tend to be reasonably priced, and it’s always worth changing all of them at the same time.
Hopefully, that fixes your misfire. If not, the cause may be an ignition coil or another wiring issue.
The coil packs send electrical charges down to the spark plugs.
If they aren’t doing this, the spark plugs won’t be sparking, and thus the air/fuel mixture won’t be igniting.
This situation also leads to carbon buildup on the spark plugs’ ends due to excess fuel not being burnt.
The most helpful tool you can have here is a multimeter. Check the readings and continuity across the coil packs and compare them against the expected readings. Each car uses different kinds of coil packs, and so it’s best to check for specific advice for your exact vehicle before carrying this out.
Again, be very careful when working with electrical systems.
Once you’ve determined a fault in the ignition coil, it needs to be replaced. You’ll have to buy a new part. Expect to pay somewhere between $50 and $250, depending on the type.
Some systems use “pencil coils” – there’s one separate ignition coil for each cylinder, and you can remove them one by one. With these, you can replace just one and leave the rest. However, many cars use coil packs – these are all “stuck together” in one unit. You’ll need to replace the whole unit.
The below video explains ignition timing in relation to tuning.
Ignition timing systems dictate when the spark plug should fire during the engine’s revolution.
Occasionally, something can go wrong with the ECU. It’s possible for the spark plugs to either not fire or not receive sufficient voltage to fire because of this.
This one’s a bit harder to diagnose yourself. If you really can’t find the problem with anything else, your thoughts should start to sway this way.
To be fixed, an electrical engineer – a specialist – will have to look at your car. The ECU is likely to need reprogramming. Unfortunately, this can cost hundreds if not thousands of dollars.
If you have an older car and it still uses a distributor, these are easier to work with. Click on this link to learn more about them on Wikipedia. If you know your way around them, you may be able to replace or even repair one of these yourself. Expect to pay approximately $50 for a new part.
Much of YouTube might make you think that all cars have distributors and distributor caps – they don’t. Not any more.
Check out this video. Most new cars don’t have distributors these days, but this is how one looks.
Cylinder Compression – Engine Misfire Causes
Uh oh. If this is what has happened, it’s the worst-case scenario, unfortunately.
Cylinder compression issues lead to misfires because the combusting air/fuel mixture’s pressure leaks out, rather than exclusively driving the piston down.
You can test your cylinders’ abilities to hold pressure with simple kits from automotive hardware stores.
If you find a cylinder that isn’t holding pressure, it indicates some internal structure breakdown. There could be a problem with a piston, a piston ring, the head gasket, or a con-rod; there could also be something as severe as a hole or crack in the cylinder walls.
Whatever the problem is, you’ll likely need a full engine rebuild even to diagnose it. That’s not cheap, sadly. Expect to pay a couple of thousand dollars, most of which is made up of labor costs.
Failing that, you might need to get an entirely new engine. This is likely to cost about the same amount, if not slightly more, depending on your vehicle.
Air/Fuel System – Engine Misfire Causes
The most likely thing within the air/fuel system to lead to a misfire is a faulty fuel injector. If the fuel injector isn’t working, there won’t be any gasoline in the combustion chamber. When the spark plug sparks, it’s trying to ignite air alone and therefore not doing anything.
You can use a multimeter to check the fuel injector’s performance and replace any that are faulty.
If there’s some issue with a camshaft or one of the valves or valve seals, in particular, they may not open. Once this happens, it means there’s no air getting to the combustion chamber, and a similar problem occurs. If you know how to, you can check them yourself.
Alternatively, never be embarrassed to take your car to a mechanic to look for you. Checking and/or replacing these parts might be a little more complex than others.
Is A Misfire A Common Engine Problem?
Misfires can happen to anyone at any time, no matter how well you look after your car. It doesn’t matter whether you drive a Ford or a Lambo, a Volkswagen or a Ferrari; everyone is likely to suffer this problem at some stage.
The silver linings of misfires are that, although frustrating and sometimes difficult to pinpoint the exact cause, they are often relatively cheap to fix. Especially if you can do it yourself.
Misfires are usually problems that can be quickly and cost-effectively repaired by either yourself or a professional. For you and your wallet, that’s great.
If your car has developed a misfire, don’t panic. As long as it still has enough power to get up hills, you’ll be fine to drive home or to the nearest shop. Once there, get the problem investigated, diagnosed, and fixed, and then you should be on your merry way again.
Should I Get It Fixed Immediately?
As I alluded to in the previous section, you’ll usually be alright to drive the car home or to a garage if it develops a misfire while you’re driving. In a standard 4-cylinder engine, one cylinder misfiring – or even two – will make the car feel a bit sluggish and off-balance. However, it should still be able to put out enough power to get you home safely.
In the end, though, you’re the judge. If the road conditions are too dangerous, find somewhere safe to pull over and either call for assistance or wait until it’s safe to drive again, depending on your circumstances.
If you’re in any doubt about your own safety and that of others, it’s not worth the risk.
That aside, if you manage to get your car home or to a garage, it’s essential to now get the problem solved as soon as possible. The manufacturers didn’t design the engine to run on however-many cylinders you’ve got left. Therefore there’s always the risk of long-term damage if you drive it like this.
The longer you drive a car with an engine misfire, the more problems you could end up with.
I would always recommend getting it fixed as soon as possible.
Can Diesel Engines Misfire?
Diesel engines can misfire. Yes.
Although we tend to associate misfires with spark plug issues, that’s not the case. A misfire is a cylinder that isn’t producing power – the air/fuel mixture isn’t combusting, for some reason. It isn’t limited to gasoline engines.
When there are misfires in diesel engines, it’s usually down to either the injectors, the injection timing, or the cylinder compression.
What Are Some Good Ways To Prevent Engines From Misfiring?
In the same way as it’s impossible to prevent humans from ever getting hurt or sick, it’s impossible to completely prevent a car from developing a misfire. As my Dad says, “Even if you stay in bed all day, you’ll get bed sores.” That is, whatever you do with your life, there is always some amount of risk.
All you can do is lower the risk as much as is sensibly possible.
With cars, this essentially just involves regular maintenance and, whenever possible, not absolutely thrashing your engine. Although it might look cool and there’s no crime against it, redlining your engine isn’t good for it.
As for regular maintenance, you should have your oil changed as often as the manufacturer recommends. Keep the engine bay – especially the top – clean and replace your spark plugs at regular intervals. Make sure you also drive with the engine at high rpm sometimes. In my experience, this is almost as effective at cleaning out carbon buildup as additives but costs you nothing.
That’s it, really. As with any piece of equipment, the more you take care of it, the more it’ll return the favor. And vice versa.
I hope this article has been helpful for you.
Engines are complicated pieces of kit and, although the basic principles have remained the same for well over one hundred years, they are now incredibly advanced.
An engine misfire isn’t uncommon and, if your car has one, most mechanics will be able to help you immediately.