my motor smoked. had it checked, said hi low stuck open in #5. replaced #5 injector, wire harness, and valve cover gasket. then not only smoked but ran very ruff. tested agin, no more hi low buy contibution test #5 low. compressoin test #5 200psi , half of what it should be. put in a motor with 45,000 miles, old motor had 198886. i know it should get more then that but my point is you should do a compression test, it won't lie. who ever had the truck before me was driving it without #5 and scared the cyclinder. maybe if you just got the truck, could have same problem? i had no knock though.