How do I correct a Code 54? Fuel pump relay circuit voltage low...

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New engine installed, new distributor, coil, plugs, wires, fuel pump/filter, truck work fine for 4 mos. Now it will crank but not start. There is fuel to the TBI, used noid light on injectors, have spark to plugs, new relay. Will start and run when using starter fluid. I get a Code 54 and Code 43 knock sensor, replace knock sensor. Fuel pump comes on and shut off, also replace oil pressure sender. Could I have a bad ECM? thanks