How To Diagnose an Engine Misfire?

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  • Post last modified:September 11, 2021

Misfire in the engine is a common problem. Misfire can severally damage your car engine.  There is some study that shows misfire can cause loss of 25 percent of engine power output. This is a huge portion of the engine power. This can affect the whole car’s performance.

Your car fuel consumption will be high and due to poor mileage, you will face various problems. Like you are driving smoothly then all of a sudden engine misfires and your car engine starts to shake and buck. It is not easy to diagnose an engine misfire. So let me give you step-by-step lessons on how to diagnose an engine misfire.

How to Diagnose Engine for Misfire?

Normally an engine misfires when it cannot burn the air-fuel mixture properly. But you may think it is easy to fix it but let me tell you that it is not that easy to do so. Misfire can occur for many reasons.

But, you cannot completely 100 percent surely say that this is the only reason that causes the misfire. Now we dig deep on this topic.

Symptoms of Misfire

These are the symptoms that you will notice if your engine misfire. In modern days engine, you cannot say for sure that your engine is misfiring by only hearing the sound of the misfire.

  • Engine loses power
  • The engine is hard to start
  • Fuel consumption increases
  • Emissions increase
  • The engine produces popping sounds
  • Exhaust manifold backfires
  • Engine vibrates, stumbles, and sometimes jerks.
  • Engine stalls

Reasons Behind Misfires

If there is no fault in the car your engine will not misfire. There are some common reasons for engine misfires. A misfire normally created for the following reasons.

  • A component failure in the ignition system.
  • Problems in the fuel system.
  • Vacuum leaks.
  • Compression drop in one or more cylinders.
  • Problems with key valves or sensors the car computer uses to calculate the correct air-fuel ratio.
  • Warn off park plug.

Now you know about both the symptoms and reasons, now it time to get back to how to do a diagnosis. Before you start it you must know something more.

How to Do The Diagnosis?

Till now I gave you information about the symptoms. Now we start the hard part, the diagnosis parts. So 1st of all you must find out when your car’s engine starts to misfire. You can find these scenarios.

  • Only misfires when the engine is cold
  • Only misfire when the engine warms up to get too hot.
  • Only when accelerating.
  • It happens consistently
  • Only when it rains or the weather is cold.
  • Engine misfires randomly

Now we start the diagnosis for these scenarios. We will start from the most common reason of misfire the fault in the spark plug. We go through simultaneously from one to another.

Spark Plug

Spark plug gives the spark that helps to burn the air-fuel mixture at the cylinder or cylinder. The spark needs to be pinpoint accurate. But, if there are some problems in the timing of sparks then it is possible the reason behind the misfire is the spark plug.

You will need a cheap spark plug tester for this. The spark plug may be loose, you must check that first. See if the sensors of the sparks plug are working properly.

Ignition Coil

Sometimes the ignition coil can wear off. Even if only one single-coil wears off it can cause multiple misfires. It will surely cause an internal misfire. If the engine has a COP coil then you must check the P0200 code series for your investigations.

You must check the ignition control module. This is one of the tricky to check, if the misfire happens in the one or two-cylinder, you can swap the suspected one with the good one for a quick check.

Check the ignition timing also. Sometimes Ignition timing becomes advanced and therefore causes the misfire. Modern cars have sensors for maintaining the timing, if the timing is not right you must check the sensors.

Older cars have distributer for this job. If you have an old one you have to check the cap and rotor for cracks, corroded terminals, and carbon traces. These things can be the reason for misfires.

Check the Fuel System

A misfire can happen if the air-fuel mixture is not perfect. It can be either too thin or thick. We need a proper mixture of air and fuel. If there is a leak in the fuel system it will be highly unlikely if you get the proper air-fuel mixture. There are many reasons to have blockage or leakage in the fuel supply system. If there is a fault in the fuel filter, it can be possible to get dirt in the fuel.

Impurities and low-quality chemicals can damage the fuel supply line. These things can damage fuel injectors also. So, it is easy to say that find out if there are any problems in the fuel system that is causing the misfire.

Check the Vacuum Systems

A leak in the vacuum also can cause a misfire. If your car misfires while you driving at a slow speed that indicates that there can be a leak in the vacuum system.

Checking the vacuum system for leaks is quite easy compared to fuel line check. You have to look for a lose-connection, check the hose for cracks. Check the hose with your bare finger, if it feels too hard or soft then change the hose.

Start the engine and push break, hear the sound carefully. A hissing sound can prove that there is a leak in the pipe.

Your hose gasket can leak also. Put your car engine at idle and put your ear on the one end of the hose. Use the other end to follow the length of a vacuum hose or the edge of a gasket area. If you heard a hissing sound then you found the leak.

What If You do Not Find Anything?

If this type of scenario comes up that there are two kinds of things that can happen. One is either you miss something or the problem is in the sensors.

There are lots of sensors in modern cars. You should look at the MAF (Mass airflow) Sensor, Oxygen (O2) sensor, Engine Coolant Temperature (ECT) sensor; throttle Position Sensor (TPS).

In the end, good maintaining of a car can prevent any kind of misfire. As you can see from the above it is not easy to find the main reasons for a misfire.

It takes a lot of time and hard work to fix the problems. The best way to prevent misfires from occurring in the first place is to perform adequate car maintenance.