Has your car started to backfire? If so, it can raise concerns that your car has a serious defect. It can also be annoying and somewhat embarrassing.


What causes a backfire?


The chances of most modern fuel-injected cars ("port" or "direct") backfiring are very low because of the way their intakes are designed. But older cars can be susceptible to backfiring.


Spark plugs in the wrong place


If your spark plugs are incorrectly installed it will cause the pistons to fire out of order. For example, if spark plug 1 is placed in the position of spark plug 4, it will ignite the air-fuel mixture in the wrong piston (4) and pass through the carburetor.


Bent valve


Poor piston timing might damage a valve, which results in a leak, causing a detonation in the piston which spreads into the carburetor.


Poorly-adjusted ignition timing


This happens when a spark is fired while the corresponding intake valve is still open. This creates a flame that ignites the air-fuel mixture and travels back through the carburetor - the backfire. This is one of the least likely causes of a backfire.




Technically, a "backfire" in the exhaust system is called an “afterfire”. Typically a flame is emitted from the exhaust pipe. Here are the main causes.


Rich air-fuel mixture


Too much fuel and too little air means some fuel can pass into the exhaust, and will, if it's hot enough, cause a combustion in the exhaust pipe.


Ignition delay


If ignition occurs in the piston too late, the explosion can continue into the exhaust manifold - creating an afterfire.


Lean air-fuel mixture


A lean air-fuel mixture burns more slowly than a rich air-fuel mixture. This can mean combustion takes place for longer, spreading into the exhaust system and firing out of the exhaust pipe.


A lean air-fuel mixture could be caused by:


     A fault in the ECU (Engine Control Unit)


     Vacuum leak - causing excess air and thus a low air-fuel mixture.


     Fuel injector defect - when the injector does not inject the right amount of fuel (too much air).


     Fuel pump fault - meaning the amount of fuel entering the engine is insufficient.



Is backfiring bad for cars?


If your car backfires or afterfires it is unlikely to cause any damage to your engine or exhaust system. However, such a scenario does mean there is already a fault in one of your car's components, and it should be addressed swiftly - if only to stop the loud bangs coming from your exhaust.