Engine Misfire Issues – Causes, Symptoms, Diagnosis, Potential Damage

Engine Misfire Issues - Causes, Symptoms, Diagnosis, Potential Damage
Engine Misfire Issues - Causes, Symptoms, Diagnosis, Potential Damage

Engine misfire issues always cause engine performance to suffer. As well as fuel economy, emissions and idle quality.

When a misfiring vehicle is subjected to an emissions test; it will usually fail.

This is what happens when you feel your engine stops for a fraction of a second; then regains its momentum.

Also, engine misfire issues can be constant or intermittent.

So, no engine fires every cylinder 100 percent of the time. Consequently, a few misfires are to be expected and should not cause, major performance problems. But, if misfires occur too often, they can make the engine idle or run rough. More seriously, engine misfire issues can cause damage to other engine parts. Like the oxygen sensors or catalytic converters.

Engine misfire is the name for what happens; when a engine skips over one of the processes of its combustion cycle.

This generally causes the engine to run rough, jerk or buck. Consequently, causing the engine to run inefficiently.

Engine Misfire Issues, What Can Cause Them ?

There are a number of issues that can cause engine misfires. Your engine depends on dozens of parts and systems to work together simultaneously. And, with precise timing in order to function as intended. Engine misfires can be caused by many faults. But, there are a few that occur more often than others.

The most common causes are:

  • Loss of spark.
  • The air/fuel mixture is too far out of balance to ignite.
  • Loss of compression.
Low Compression Causing Engine Misfire Issues
Low Compression Causing Engine Misfire Issues

There are other worse causes:

  • Computer or wiring problems.
  • Breakage in the rotating mass (pistons, rods, crank bearings).
  • Valves and cylinder heads can fail or distort.
  • Cooling difficulties might permit overheating.
  • Leaking or blown gaskets.

Engine Misfire Issues, What Are The Symptoms ?

Symptoms usually vary by vehicle type. But, are usually described as; a stumble or brief hesitation, in power delivery. An engine misfire can be temporary or continuous. And, will sometimes generate a check engine code.

The following are the common symptoms of engine misfiring issues:

Poor Acceleration

When a misfire occurs, you can feel it; like a light or massive jerk coming from the engine. Most of the time they are worse under load. Rough acceleration is also, a typical sign that your engine is misfiring.

Lower Than Normal Fuel Economy

Lower Than Normal Fuel Economy
Lower Than Normal Fuel Economy

Decreased gas mileage is also one of the issues. Poor gas mileage, especially a sudden drop in fuel efficiency; can be blamed on a number of issues. It can also be an indicator of a much more serious issue; that can develop into an expensive repair. There are dozens of other problems that can lead to a drop in gas mileage.

Rough Engine Idle

If your vehicle is experiencing rough idling, you’ll probably know it immediately. While some cases are less severe than others; a rough idle is usually identifiable by, a shaking and bouncing sensation. You may also notice odd sounds. As well as an inconsistent (RPM). Normally, a vehicle should have a smooth and consistent (RPM) rate of around 1,000.


During a misfire, the engine will begin to shake. Misfires don’t always happen consistently. So, the vibration may come and go under different driving conditions.

Check Engine Light On

Check Engine Light On
Check Engine Light On

If your car has poor acceleration; as well as consuming more fuel than usual; check for any engine codes. That warning light on your dash is the vehicle’s computer. It will let you know that it is seeing something wrong.

Engine Misfire Issues, Diagnosis ?

The common misfire can be classified into one of three different categories:

  • Your fuel system.
  • Your ignition system.
  • Mechanical issues.

Fuel System

If your ignition system checks out, then move on to your fuel system. Misfires related to fuel system issues are far more noticeable; at idle or low-speed driving. Not enough fuel getting into your cylinder; leading to an oxygen heavy explosion. There are a number of components that regulate, how much fuel enters a cylinder.

Ignition System

When air and fuel combine in the cylinder; they need a spark in order to ignite them. When they don’t get that explosion; the cycle still continues; and more air and fuel combine. In most cases, this simply means you have a faulty or intermittent spark plug. As spark plugs wear and corrode; they lose their ability to ignite on command. In most cases, replacing your spark plugs and or wires; will solve a misfire problem.

Mechanical Issues Including Loss Of Compression

Finally, mechanical issues could be what’s causing your misfire. First, check your vacuum lines connected to the intake manifold. Make sure they aren’t leaking or cracked in some way. There’s also a chance your timing belt or chain may have jumped or slipped. Loss of compression will cause it to lose most of its air/fuel mixture; before it can be ignited.

Burnt Exhaust Valve Causing Engine Misfire Issues
Burnt Exhaust Valve Causing Engine Misfire Issues

The most likely cause is a leaky (burned) exhaust valve or a blown head gasket.

If two adjacent cylinders are misfiring; it’s likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant; it’s likely the head gasket is leaking.

Head Gasket Leaking Between Cylinders
Head Gasket Leaking Between Cylinders

Engine Misfire Issues, What Potential Damage Can They do ?

Damaged Oxygen Sensor

Oxygen Sensor (O2) Failure Symptoms Chart
Oxygen Sensor (O2) Failure Symptoms Chart

Oxygen sensors are used to measure the amount of oxygen in the exhaust gas. However during the misfire, the fuel mixture remains unburned. As a result, causing damage the sensors as well.

Damaged Catalytic Converter

Catalytic converters can overheat; because of excessive amounts of unburned fuel. Usually caused by a misfiring spark plug or a leaky exhaust valve. In addition, a faulty oxygen sensor can cause overheating.


So, get in the habit of conducting regular vehicle maintenance. It will extend the life of your engine. Finally, you can handle basic routine vehicle maintenance yourself. Always follow a regular schedule as outlined in your owner’s manual.

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