Engine Backfires While Driving

The engine backfires on the tail pipe while driving mainly because of the problem on the air injection system, another reason is the valve is not sealing or the engine timing is off.

Possible Cause of Engine Backfiring while Driving

There is a Problem with Air Injection System 

When there is a problem with air injection system, the engine backfire trough tail pipe when the car is decelerating. Air injection system is an emission control device that pumps fresh air going into the exhaust manifold so that unburned gasses will burn before it goes out the tail pipe into the surroundings. It has a component that called the air injection system diverter valve. If the diverter valve fails it can cause the engine to backfire through the tail pipe.

Now when the car decelerates the air/fuel ratio is rich, which means that there are a lot of unburned gasses going into the exhaust manifold. If the unburned gasses are mix with the fresh air it can cause a mini-explosion or backfire. It is the purpose of the diverter valve to divert the flow of fresh air away from the exhaust manifold when the car is decelerating. With that said if the diverter fails the engine will backfires when the car is decelerating.

Bring the car to a reputable car shop and ask the mechanic to check the air injection system, specifically the air injection diverter valve and repair or replace if necessary.

The Valve is Not Sealing or the Engine Timing is Off 

If the backfiring did not happen when the car is decelerating then the possible problem is that the valve is not sealing or the engine timing is off.

When the valve is not sealing some of the fuel will leak out into the exhaust manifold, now if the manifold is hot the fuel will be ignited and the sound that is created will comes out the tailpipe.

Also, if the engine timing is off, the spark that comes from the spark plug will occur even when the valve is partially open and part of the air/fuel ratio mixture will burned on the exhaust manifold. The sound that is created will then be heard through the tail pipe.

Bring the car to a car shop and ask the mechanic to check the valves and the timing. Usually the valves are burned or the valve will only need a simple adjustments. As for the timing that is off, the chain or the belt is slipping or worn and need to be replace.

See also: Engine Backfires when Starting