What is an Engine Backfire?


Backfiring occurs when unburned fuel ignites outside of the internal combustion engine instead of inside a cylinder. This could be for many reasons both mechanical and / or air-fuel ratio.  If the combustion goes wrong there is a loud bang and sometimes fire or smoke is released which if strong enough can cause damage to intake or exhaust components of the car.


What are the Causes of an engine backfire:

  • Vacuum leak – A vacuum leak is created by the engine’s pistons pumping inside the cylinders. The vacuum is filled by the air drawn in through an intake system. A leak in an engine part after the air intake creates additional air that is not being noticed by the engine computer which can trigger the “check engine light” because there is more air than necessary causing the car to run lean. For more information on Vacuum, leaks click here: Vacuum leak
  • Running rich – Opposite to running lean running rich is when the engine has more fuel than it can burn. When this happens the unburned fuel can’t be forcefully burned by the extra air and will be spat out when the exhaust valve opens. This can cause a backfire and is most commonly caused by a dirty air filter.
  • Bad timing – If the fuel-compression-ignition-exhaust is out of sync with the other parts of the cylinder e.g igniting before the exhaust valve is fully opened a backfire can occur due to the lack of timing.
  • Cracked distributor cap – A car without ignition coils on the spark-plugs may have a distributor cap over the spark-plugs. If this cap becomes cracked then it is possible for moisture to creep in, which causes electricity to jump to the wrong cylinder which can lead to a backfire.

For a guide to how to diagnose the problem with your car backfiring click here:
Car Backfiring – Diagnosis and troubleshooting


Symptoms/ consequences of backfires

A backfire is usually accompanied by a bang or a loud noise from the engine or exhaust. If the noise is really loud then this could potentially mean damage to the cars intake or exhaust system. If the car exhaust is smoking after backfiring then the car might need to be checked. If the car is putting out black smoke then the car might be running rich or the spark plug might be covered in soot or partially damaged. A little bit of light white smoke after a backfire does not mean that the car is damaged in any way and can be the engine warming up. However, if there is constant white smoke there could be a problem with the engine and could be a symptom that there is a problem within the intake manifold or head gasket.

Engine backfires diagnostics & servicing in Hamilton

Is your car backfiring and needing an inspection? If so, we can help! At Grimmer Motors, our team of skilled mechanics can quicxkly diagnose the issue, then service the various parts of your car’s engines intake and exhaust system. The results can greatly improve the operation of the engine and keep your vehicle safe from costly repairs.

For engine backfire diagnostics services in Hamilton, contact Grimmer Motors today!


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