Why would there be leaking behind the fuel injectors or the throttle body?

What is your question?

Also my truck backfires when I press on the pedal too hard, it bogs down, idles up and down...not consistent, wont stay started, sometimes has a rich smell, check engine light will sometimes come on and fuel consumption is worse. Have changed spark plugs and wires, starter, water pump, oxygen and coolant sensors and battery. I have read so many different things could be causing this...just not sure what exactly. So I thought I would ask and see what ya'll think could be the problem. Thanks!