rover 416 k series non start ?

can any1 help, have a r416 is k series engine, vehicle started missing a beat then got worse to the point of when accellerating fully vehicle lost all power until acce llifted then regained drive!, have replace fuel pump. spark plugs, fuel filter, oxygen senor coil and leads and dist cap and rotor arm all in the last year vehicle has park and fuel now just turns over and wont fire up, any ideas ???