After washing oil from engine it started backfiring and eventually stop running

For what I can understand the engine was washed and rinsed with water. IF that is that case, my feeling is that some vital electrical connectors got water in them and now they cannot make a good contact thus no spark thus the wet spark plugs. you will need compressed air to clean the connectors. If that does not work you will need to bring it to a shop. Carlos M. call me for more info if you'd like 818 701 4061. Omega Automotive.