It is decelerating any time it is not accelerating or is stopped. Decelerating means slowing down.
Signs of a worn timing chain are difficulty starting in cold weather with backfire and sudden brief loss of power while accelerating or decelerating ("stumbling").
It can mean that this engine is out of time. You may need to have it timed.
while driving yur car reduces speed then pulls off with speed and backfires what can cause that
That usually means it's lean. Check all vacuum lines and gaskets for leaks.
Backfire is an explosion produced by a running internal combustion engine that occurs in the intake or exhaust system rather than inside the combustion chamber,
When a car slows down at a traffic light, it is decelerating. This means that the car is reducing its speed or coming to a stop in response to the signal.
A car can backfire and die if the spark plugs are bad. The car could also have a problem with the timing or the catalytic converter .
When the car is coming to a stop, it is decelerating--or it has negative acceleration.
Slowing down or decelerating
Because you are decelerating sharply
Probably a major backfire.