Just like the title says, the ECU will not trigger the fuel pump relay to prime the injectors. When the truck is cold it fires and runs great. Once the truck reaches operating temperature, it wont start unless i pour fuel down the throttle body to start it. Once the truck has started the ecu signals the fuel pump to run as it should. I have tested voltages to the relay, and it is doing its job when the truck is running. If I use a wire to trigger the relay manually, the fuel pump runs and the truck starts right up. What circumstances/sensor would cause the ECU not to trigger the relay when the vehicle is hot?