Vauxhall Astra car willnt rev above 4000rpm and engine light is on all the time

my car willnt rev above 4000rpm and engine light is on all the time when i got the car the head gasket was away so we fitted a vectra 1.6 16v engine it ran fine for 2 weeks but now it limits at 4000 rpm and i think its gettin way 2 much petrol we have changed the throttel body crank sensor coil leads plugs and its still doing it gose to 4000 rpm them limits if its not fixed soon it will gan on ebay lol