How to Fix Misfire Engine – Top 4 Easy Parts Replacements

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Engine misfires in a car are frustrating and dangerous if left unchecked. Not only does it limit the performance of your car, but it can also damage your engine resulting in an expensive repair cost. In this article, we’ll teach you how to fix an engine misfire. Most of the methods are cheap and easy and you can do it yourself. However, the challenge is diagnosing the issue and ensuring that you found what is causing the misfire.

You must have knowledge of the ignition system as well as car repair experience. This is an advanced repair guide, so please proceed with caution. Moreover, every car is unique. That is why you should investigate more about the misfire issues on your car model. And remember to always refer to the manual and don’t hesitate to ask for professional mechanics’ help.

What is an engine misfire?

Before we discuss what an engine misfire is and how to fix it, let us first explore how firing order works in your car’s engine. As we all know, petrol cars need an internal combustion engine (ICE) to run. A proper engine firing requires a spark, fuel, and air to work together and produce combustion. If one element is not doing its job or malfunctioned, an engine misfire occurs. It can happen suddenly while you are driving or could be a persistent problem. Fortunately, most modern cars have a computer to detect this problem.

OBD 2 Codes

On-board diagnostics II (OBD 2) checks your engine and other systems and reads all the possible problems that happen to them by generating a code. It is wise to have your own OBD 2 scanner and learn how to read the codes. Some scanners provide an English description. If this is not the case, you may refer to the manual or the manufacturer’s website.

However, keep in mind that OBD 2 misfire detection does not tell you why the engine is misfiring. Instead, it gives you an exact count of the misfiring cylinder by cylinder. It can only help you investigate and narrow down the cause. The scanner will either give you an error specific to one cylinder misfiring, or a generic misfire error across all cylinders.

Most common OBD 2 codes regarding misfire engine:

P0300 – random misfire code (multiple cylinders involved)

P0301 – misfiring in cylinder 1

P0302 – misfiring in cylinder 2

P0303 to P0312 – misfiring in cylinder 3 to cylinder 12

A code ( P0300 – P0312 ) may mean that one or more of the following has happened: Bad, spark plugs or wires

1. Faulty coil (pack)

2. Failed oxygen (O2) sensor(s)

3. Faulty fuel injector(s)

4. Burned exhaust valve

5. Faulty, catalytic converter(s)

6. Stuck/blocked/leaking (EGR) valve / passages

7. Faulty camshaft position sensor

8. Defective computer

The following codes might help you pinpoint the cause of misfires and it’s worth investigating further. Keep in mind that this code might because of other issues aside from engine misfire.

P0200 – injector error code where 0201 means injector 1 and so on

Related: If One Fuel Injector Is Bad Should I Replace Them All?

P0401 – This is an EGR error code and others basically mean carbon buildup under the EGR valve (P0400 series).

P0171 or P0174 – This is a lean code and could mean a dirty or clogged fuel injector.

What causes engine misfires?

As discussed earlier, engine misfiring is usually because of one of three issues: loss of spark, poor air-fuel ratio, or loss of compression. As a result, one or more of the cylinders would fail to fire.

1. Faulty spark plugs

Faulty spark plugs are one of the leading causes of engine misfires. Spark plugs can get soiled from oil leaks and carbon buildup. They also wear down faster than normal due to overheating and wide gaps from the plug. Sometimes wet weather can also be a factor. However, this misfire may disappear if the engine heats up and the moisture dries.

2. Worn distributor cap

Second, it can be due to a carbon track because of a worn distributor cap (if you have one). The plastic cap is supposed to be an insulator. This is called carbon tracking, which causes a low-resistance conductive path through the plastic. This could also lead to misfiring or firing the wrong order of the cylinders. If you notice any crack in your distributor cap, you should replace it immediately. Moisture within the spark plug wires could also lead to misdirection of the current.

3. Ignition coil

An induction coil transforms the battery’s voltage to create an electric spark in the spark plugs to ignite the fuel. They can be worn off sometimes. Moreover, even if one coil wears off it can result in multiple engine misfires. If your engine has a COP coil then you may check the code series P0200 to investigate further.

4. Lean fuel and air mixture / Vacuum leaks

Finally, a lean fuel and air mixture are harder to burn. If there is a carbon build-up in a cylinder, it will increase the compression ratio making it harder for the spark plug to fire. Moreover, if there are vacuum leaks in one cylinder, it may cause a misfire. Because of the leak, there will be additional air reaching the cylinder. This will dilute its air/fuel mixture.

In some cases, the bad coolant temperature sensors can cause misfires too. The sensor is used to measure the temperature of the coolant and send it to the ECM. The ECM then uses this information to adjust the fuel ratio, ignition timing, etc.

How to Diagnose Misfire Engine

Spark Plugs

As spark plug issues are one of the most common causes of engine misfire, it is practical to have a spark plug tester. A spark plug tester is a cheap tool that allows you to check if your spark plugs are still working properly. It is a time-saver to immediately check if the cause of the misfire is in your ignition. It can also save you time by allowing you to pinpoint the problem.

Ignition Coil

Check the ignition control module. To quick check, a suspected coil that may cause a misfire in one cylinder, just swap it with a good one. You should also check the ignition timing. There are instances where ignition timing is advanced and causes a misfire. Timing sensors found in modern cars can help car owners diagnose the cause of the misfire. On the other hand, older cars have a distributor for this job. Just check the cap for any corrosions and carbon tracks that may be causing engine misfires.

Vacuum Leaks

Find leaks using a spray bottle with water and dishwashing soap. Spray a cold engine along the vacuum lines, PCV valve, and intake manifold gasket. Start your engine and observe for any bubbles. If the RPM changes when you spray the area again, it means there’s a crack in the hose.

Don’t have an OBD2 scanner yet? Here’s a video tutorial on how to diagnose engine misfire without a scanner:

How to Fix Misfire Engine

The challenge in resolving the issue is to find the cause. This guide will teach you how to fix the misfiring engine. Before you proceed make sure you are 100% sure that you have diagnosed the car correctly and found the cause why the engine is misfiring. Always refer to your car’s manual as messing with the car’s engine may cause more harm than good. Make sure you know what you are doing before you proceed.

Spark plugs

If you have done all the diagnostics above and found the spark plug is the culprit, then simply buying a new one will fix the misfiring engine. This fix is the cheapest and the easiest. They are as low as $10 a piece and can be changed in about an hour. For a guide on how to replace spark plugs, please check our article on car repair and maintenancesIt is best to replace all spark plugs at once to achieve consistent performance.

How long does spark plugs last? Some spark plugs now have a service life of up to 100,000 miles.

Spark plug wires

You should also consider replacing your spark plug wires. It will be easier since you will be working in the same area and you have to remove the wires to replace the spark plugs. Moreover, they are affordable too. A set of spark plug wires costs about $30 to $80. By the time you need to replace worn-out spark plugs, the wires are plausibly due for replacement too.

Ignition coils

Your ignition coil can be found by following the spark plug wires from the distributor. It can be pop off by removing a coup of bolts and electrical connection. Depending on the age of your car, you either have one coil or more than one. Failing coil to plug ignitions will cause erratic kind of miss and roughness. Ignition coils are more likely to fail if spark plugs are old and worn out. A failed ignition coil can damage your catalytic converter or even the engine computer (PCM).

In most cars with a 4-cylinder, replacing an ignition coil is simple. It can cost about $75 to $300. Labor cost is between $50 and $100 per hour. To prevent future problems, your mechanic may recommend replacing all three rear ignition coils. You can easily replace them at home but you must be cautious and disconnect your batteries first.

Vacuum Leaks

If you found out that you have a failing intake manifold gasket, you may replace it on your own. Here is a step-by-step guide from advanceautoparts.com. Make sure you have intermediate knowledge and a repair manual before you proceed.

Here is a step by step guide on youtube.com:

In terms of cost, the gasket itself is very cheap from $20 to $120. If you need a mechanic to install it, it would cost $200 to $600.

How much does it cost to fix a misfire?

Now let us summarize the costs of each repairs methods on how to fix misfire engine. The model and year of your car will affect how much mechanics are going to charge you for their service. And of course, a repair shop may charge you $50 to repair a spark plug, while others will charge double for that. To have a general idea, this is what you can expect for some common causes of engine misfires:

Parts

1. Spark plugs – $10 each / $60 per set (6 pieces)

2. Spark plug Wires – $30 to $ 80

3. Ignition coil – $75 to $300

4. Intake manifold gasket – $20 to $120

Labor

1. Spark plug replacement – $45 to $100

2. Ignition Coil – $50 to $100

3. Intake Manifold Gasket – $200 to $600

Total Parts Cost: $130 to $500
Total Labor Cost: $250 to $700

Conclusion

A misfiring occurs when a spark plug doesn’t fire or sometimes it fires in the wrong cylinder at the wrong time. If not fixed immediately, engine misfires can damage your engine. The most common cause include worn-out spark plugs, wires, or vacuum leaks. To diagnose it properly, it is best to use an OBD 2 scanner to get the codes and narrow down the cause. Before you proceed make sure you are 100% sure that you have diagnosed the car correctly and found the cause of why the engine is misfiring. How fix a misfiring engine is as easy as replacing the cause of the misfire. Again, correct diagnosis is crucial. If you have good repair experience and knowledge of how the ignition system works, you might as well do it yourself and save as much as $700 in labor costs.

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