i get code po281 what can cause it

Question

motor missing and and virates but no noise are rod knock sounds normal other than runing bad it shows code po281

Answer 1

This code is the cylinder balance test where the number 7 cylinder is identified as not contributing, Yes it does run rough and there is a terrible noise, You try this is not a fool proof test but it the direction if the injector or engine, with the engine running open the oil cap if it get worse its a sticking injector