I replaced an Isuzu 4HL1 common rail engine dual mode. I replaced it because it sucked water and the block was damaged. I used all the other components from the old engine. Such as the fuel pump and the gallery. But this problem occured: first it takes few seconds to start and than when the REV counter goes up to 2000 and 3000 RPM it works fine but when it goes down again to 1000 RPM the engine goes off. I need your help! The ECU is fine and when we attached the computer it didn't give us any faults. Thank You. Waiting for your reply.