Black smoke with a bang after replacing fuel filter and pump

I had the fuel injector system error coming up, as soon a I go an up hill the car switches out and everything pulls tight with lights all on, but there is white smoke visible then gone the next. Restart the error disappears and the cars goes driving fine again. it did this about five times. I took it in to the dealer they did a hoist check which revealed the fuel pump ad filter is faulty and needed replacement. They told me my injectors are fine, not even two days later the car does this again with a loud knock from the front and first white then black smoke coming out the exhaust.
what is wrong with my car? mechanic telling me I need to replace the engine. I do not feel that is right.