I have a 1998 Dicovery. I have had it for about 2 and a half years, and since then I have had to replace the entire cooling system, (machine the heads, head gaskets, hoses, water pump, etc.) I have replaced the computer that is under the hood against the front left fender, new master cylinder and booster, new ignition switch, and new fuel pump, but I still have 5 check engine codes, and it will not hit a lick. I believe it is not firing. Codes are P0158, P0300, P0420, P0451, and P1447. Any advice is greatly appreciated.

 

Have you checked for spark?
What is the fuel pressure at the fuel rail?