Tech Help > Fuel Delivery Problems Some will need to be "back flushed" Let Kent show you why some older C.I.S. fuel injectors can not be thoroughly cleaned by normal pressure flow cleaning. There is something inside the fuel injector that will need to be back flused with cleaning fluid. Watch the video to learn more. Problem & Solution Common among these chassis: R107 W116 W123 W124 W126 R129 W201