Engine misfires are not an uncommon problem and when they happen you may wonder “can a misfire ruin your engine?” Is it safe to drive after your engine is misfiring? What even caused it to happen in the first place? A lot of the time we're comfortable to just ignore a strange sound from your car if it happens only once or twice and then seems to go away. It's in your best interest to understand what causes an engine misfire though, and what if anything you need to do about it.
Engine misfires can be a very serious problem if left unchecked. Not only do they greatly limit the performance of your vehicle, they can also end up causing some extremely costly problems that effectively destroy your engine.
It can be tempting to ignore a misfire if it just happens once in a blue moon. No one wants to have to go to a mechanic because it's a stressful thing to do, and you know it's going to end up costing you money. But the longer you put off looking into the cause of an engine misfire, the worse the situation could potentially be. You'll save yourself time and money if you figure out what's going wrong as soon as you can. Before you do any of that though, it's best to know exactly what a misfire is and why it may have happened in the first place. Understanding the problem is the first step into dealing with it.
How Can You Tell If the Engine Has Misfired?
There are a handful of symptoms you should be on the lookout for when it comes to your engine misfiring. If you notice these things consistently then you definitely have a problem on your hands. Remember, don't let any of these go on for too long.
- Power Loss. A good sign that your engine has misfired is a noticeable loss of power. Your car will seem sluggish and will likely have an unusual shake or vibration that you haven't experienced normally. This is especially true when the car is idle.
- Mileage. Your gas mileage will suffer noticeably if your car is misfiring. Because the fuel is not being ignited properly and burned to accelerate the vehicle, you'll find yourself filling up the tank more often than you should.
- Acceleration. Your acceleration will decrease a lot when your engine misfires. This is because your engine is working just as hard, but you don't have the pistons pumping to provide the same amount of power any longer. In a 4-cylinder engine this can cause a significant problem. It will seem like you're putting the same amount of pressure on the gas pedal to get moving but the car won't respond nearly as quickly as it usually does.
- Sound. One of the most noticeable signs that your engine is misfiring is the sound it makes. A misfiring engine could make a sound similar to coughing or sneezing or popping. The sound is generally loud enough to be unmistakable. It can become very annoying after a while as well, not just for other drivers but for you as well.
- Odor. The final sign that indicates your engine is misfiring is an odor. Not a lot of people expect their car to be making unusual smells but when your engine misfires there's a definite scent in the air. The most notable well will be gasoline but there may be some smoke and coolant smells mixed in as well. If the damage has progressed so far that you're noticing these smells, then you should get to a mechanic right away.
What is An Engine Misfire?
Your car is powered by gasoline mixing in precise amounts with oxygen in your engine. Combustion happens in the cylinder and causes the pistons to pump up and down which provides the energy for motion. All the cylinders have to fire in a very exact sequence one after another for the engine to run smoothly. A misfiring engine is caused by that combustion reaction happening at the wrong time.
An engine will typically have anywhere from 4 to 12-cylinders. It's possible to have more, some high-performance vehicles even have 16-cylinders. But the most common are 4-cylinder, 6-cylinder, and 8-cylinder. When one of your cylinders misfires that causes a power loss in proportion to the cylinder dropping out of the entire combustion reaction. That means if one cylinder in a 4-cylinder engine misfires, you just lost 25% of your power.
What Causes an Engine Misfire?
Unlike some problems that occur in your engine, there are several issues that can lead to engine misfires. Some are more common than others, and some are definitely more expensive to fix than others.
- Bad Spark Plugs. A misfire could be caused by a bad spark plug. Spark plugs provide the spark that ignites the oxygen and fuel mixture in the engine. So, if your spark plug doesn't spark properly then there's nothing to ignite the fuel/air mixture, and that causes the engine to misfire. A bad spark plug could be caused by corrosion or bad wiring causing it to not work properly.
- Bad Ignition Coil. The ignition coil could also fail leading to an engine misfire. Each spark plug has an ignition coil which converts the 12-volt power that comes from the battery to a much higher voltage necessary to cause the combustion reaction. A faulty ignition coil will not be able to properly convert the voltage and a misfire could occur.
- Bad Fuel Injector. If your fuel / air mixture is off that can also result in an engine misfire. This can be caused by faulty fuel injector, or even an air leak somewhere in the line. Bad fuel injectors will cause misfiring across all cylinders as opposed to just a single one, however.
- Vacuum Leak. When the vacuum around your engine's intake manifold fails you can also end up experiencing engine misfires. When the vacuum has a leak, you end up with a very lean fuel mixture in the cylinder, and if it's too lean to ignite then you get that misfire.
- Worn Piston Rings. One of the more serious causes of an engine misfire can be worn piston rings. Damaged piston rings are not able to seal the cylinder properly. This can cause fuel leakage from the chamber and recurrent misfires. This can be a very costly problem to fix.
Is it Safe to Drive with a Misfiring Engine?
Strictly speaking it is not safe to drive your car if the engine is misfiring. If you notice the intermittent loss of power or poor acceleration, you should get to a mechanic as soon as possible. There are a number of dangers that can be associated with continuing to drive with a misfiring engine.
The lack of power and acceleration associated with a misfire engine could be very dangerous in tight situations. If you need to respond quickly to avoid an accident, that's no longer an option. Imagine what would happen if your acceleration was extremely limited and you needed to get out of the way of an oncoming vehicle.
The longer you drive with a misfiring engine the more likely it is that you'll cause further damage to the engine. The strain could cause the problem to cascade and result in additional cylinders misfiring to the point that the engine stops functioning entirely. That could be especially dangerous if you are far from home, like on the highway or off-roading for instance.
If your engine misfires intermittently, and the power losses aren’t sustained, you may be tempted to continue driving. It's definitely not something you want to let go for a long period of time, however.
In newer cars it's possible that a single engine misfire could put the whole car in limp mode. That's a reduced functionality mode of operation governed by your car's computer. It is like safe mode on your computer. The idea is that most systems are protected, and you have enough ability to drive yourself to a mechanic to get things repaired before the damage gets worse.
If your car goes into limp mode, you definitely do not want to avoid getting it fixed. You simply won't have the full range of operation that you're used to until you get it checked out.
The Damage Caused by a Misfiring Engine
The damage to your engine from driving with a cylinder misfire can manifest in several different ways. It will cause damage to the pistons and cylinders over time, but before that happens the catalytic converter will suffer first. When your engine is misfiring, that means the fuel entering the chamber is not burning. Unburnt fuel will enter the catalytic converters as a result, and as your engine continues to struggle to function that will massively increase the heat, damaging the converters.
Over time, because your engine is running too lean, you have to worry about the heat damage to the engine itself. The valves and pistons are not designed to handle high heat for an extended time. That prolonged, high heat can eventually even cause warping or cracking in the valves or cylinder head.
If your engine is running too rich, then the excess fuel will be saturating your engine. That will wear down lubrication on the cylinder walls which can also lead to damage over time. There is no situation in which allowing the continued misfiring of an engine won’t cause more damage.
The Cost of Repairing a Misfiring Engine
It's hard to predict an exact cost for repairing a misfiring engine. Because there are several causes, there can obviously be different costs associated with trying to fix the problem. For instance, a problem with a bad on plug ignition coil might end up costing you $300 to $400 on a newer model, four-cylinder engine. The coil will have to be replaced as well as all of the spark plugs. The price will nearly double for A 6-cylinder engine, you can expect it to go up from there for 8-cylinder and 12-cylinder engines.
Obviously, your make, model, and year will have the largest effect on how much a mechanic is going to cost you to repair certain problems. And of course, one mechanic May charge you $150 to repair a spark plug, well someone across town will charge double that. For a general idea of costs, this is what you can expect for some common causes of engine misfires.
- $100 to $300 for bad spark plug wires
- $100 to $300 for a faulty ignition coil
- $200 to $500 for a bad fuel injector
- $200 to $1,000 for a vacuum leak
- Up to $3,000 or more for broken piston rings
As you can see there is quite a range. Materials and labor costs will vary greatly from city to city, and mechanic to mechanic, so it's always best to get a few estimates before you commit to any repair costs.
Some of these could be easily fixed on your own if you have the confidence to try it. Replacing spark plugs is a fairly easy task, and they don't cost a lot of money either. The problem is diagnosing the issue and making sure that you know exactly what is causing the misfire first.
The Final Word
You don't want to let a misfiring engine go for too long without getting it looked at by a professional. If you're not 100% sure of your own abilities to diagnose and repair the problem, then going to a mechanic is the best idea.
As you’ve seen there are a number of potential causes for an engine misfire. Fixing this problem on your own could potentially cause even worse damage in the long run. the damage that your vehicle could suffer on a long enough timeline without this issue fixed is severe. You don't want to have to end up paying $3,000 to repair damaged pistons, when you could have paid just $100 or so to repair a spark plug a few months ago.