CUSTOMER CONCERN Customer states the engine misfires on cylinder 1. DTCs P0300 and P0301 are stored, and running compression measures approximately 13 psi. CAUSE Cylinder-deactivation testing confirmed the valve lifter oil manifold was not maintaining Active Fuel Management lifter operation. CORRECTION Remove and replace valve lifter oil manifold. Inspect AFM lifter and valve spring condition, clear DTCs P0300 and P0301 and verify cylinder contribution.