What is an engine misfire?

A misfire occurs when your vehicle’s engine misses a process in its combustion cycle, causing un-burnt fuel to go into the exhaust and atmosphere.  Over time, misfiring can cause damage to your engine and exhaust components, as well is increase fuel consumption, decrease engine power and increase your vehicle’s emissions.

If your vehicle has a misfiring engine, the most cost-efficient option is to have your vehicle serviced immediately. This way, mechanics can quickly diagnose and fix the problem before they cause more damage to your vehicle’s engine components.

What are the signs of a misfire in your engine?

During a “severe misfire”, you will often hear a loud popping sound coming from your engine. This popping will often be accompanied by backfiring in your exhaust pipe.

A misfiring engine has a particular smell. If you can smell petrol mixed with coolant or engine oil, you should get your car serviced as soon as possible. This is often a sign of a damaged cylinder.

Your vehicle will lose power when it misfires. This often means that the engine will shake or vibrate, particularly at different RPM. This shaking is caused by your engine’s components moving unevenly. Over time, this will increase wear on your engine and cause damage to your engine mounts. If you lose power on a busy road, this can be a safety hazard. If you have to drive a misfiring vehicle, be careful and try to avoid high long journeys, as long journeys can cause major, expensive damage to engine and exhaust components such as the catalytic convertor.

catalytic converter light on dash

This is an example of a catalytic converter dashboard warning light.

Failed catalytic convertors can cost up to many thousands of dollars to replace on many cars. Therefore it is cheaper in the long run to get a tow truck if your engine is badly misfiring (hesitating / surging), rather than drive too far.

What are the main causes of a misfire?

There are several common causes for a misfire in your engine. These include:

Ignition-related misfires

An ignition problem is the most common reason for a misfire. The spark plugs, wiring, ignition cables and ignition coils will wear over time and this can compromise their ability to ignite the vehicle’s air/fuel mixture correctly.

Air to fuel balance misfires

Engines have a recommended air to fuel ratio. When this ratio becomes imbalanced (too much air or too little fuel), a “lean” misfire can occur. These types of misfires are common when the vehicle is idling due to high vacuum, and can often go away once you reach higher speeds (lower intake manifold vacuum).

This type of misfire can be caused by a weak/damaged fuel injector, a weak fuel pump, a blocked fuel filter, a malfunctioning air flow sensor, faulty EGR valve or a vacuum leak.

Mechanical misfires

Sometimes, a damaged engine component can cause misfires. There are many different reasons for a mechanical misfire. These include:

  • Worn cylinder walls
  • A leaking head gasket
  • Damaged valves or pistons
  • Damaged fuel injectors
  • Worn or slipped cambelt/timing belt

Unlike air to fuel balance misfires, these misfires will become more intense as your car gains speed. If you suspect that you have a mechanical misfire, you should take your vehicle to a qualified, experienced and trusted mechanic as soon as possible. Mechanical misfires can cause expensive engine damage over time.

Engine Misfire Repair and Diagnosis in Hamilton.

At Grimmer Motors, we can use state of the art diagnostic tools to quickly diagnose an engine misfire of any type. We can then fix the problem and get your car running correctly again quickly.

Sometimes, a misfire can be so subtle that the driver won’t even notice. We can generate advanced diagnostic reports that determine the misfire rate of each engine cylinder. This service comes free of charge with any workshop labour or parts purchase over $49.

misfire check graph

When a misfire remains untreated, the following will happen:

  • You can see an increase in fuel consumption.
  • Your car will produce more emissions. you may notice black smoke coming from the exhaust.
  • Your car can become shaky, surge or hesitate.
  • You will run the risk of seriously damaging your engine, resulting in expensive engine or engine mount repairs.
  • You can risk serious exhaust damage. The misfires can cause the catalytic converter in your exhaust to overheat, which can costs thousands to replace.


To save money and keep your car in good condition, get your vehicle serviced with Grimmer Motors today. Contact our friendly team to book your appointment.

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