Installed a rebuilt crate engine due to a broken rod in the original engine. Old engine still ran with broken rod. Installed new engine and get code P0336. Truck will NOT run. New AC Delco cam and crank sensors. New connectors to the sensors soldered and heat shrunk. Get constant spark while cranking. Injector 3 and 4 only fire twice when cranking. All other injectors seem to fire constantly. We have checked, double checked, triple checked, and quadruple checked grounds. Have crank signal on scan tool. Swapped pcm and got the same results. We made a crankshaft sensor only harness and wired it straight to the pcm to rule out bad wiring within the harness, still no start and same code. Any ideas to help end this 4 month ordeal?