I have Toyota corolla 2000, which is difficult to start at times and it starts normal at times.... But these days I experience pop sound when starting the engine form the exhaust.. Engine of apromx. 200k miles
In my experience, a pop at start indicates excess fuel/air in the cylinder at the wrong time in the four cycle combustion process. This could be a problem in:
- valve timing (worn chain?)
- valve sealing (burnt valve?)
- or perhaps leaky fuel injectors.
Oh, and my request for a pre-start fuel pump run is to test for leaky fuel injectors.. I'd suspect you get more "pop" at startup in that circumstance...
200,000 miles on the engine is a whole lot. Frankly for that car, I'd suspect that is end of the engine's life expectancy. How long were you expecting this engine to last? How noisy is it? Any oil leaks on the ground? (both of those indicate lots of normal use engine wear...)
Backfire is caused by the exhaust system containing gasoline vapor and air from cylinders that did not fire. When a cylinder fires, flame in the exhaust ignites the vapor . If severe , it can blow open a muffler/resonator. The cat converter does not have any affect when it is cold.