You cannot place a sensitive analog voltage sensor trace next to a pin driving a high-current fuel injector. The electromagnetic interference (EMI) would drown out the sensor signal. Pinout work requires strict Signal Segregation:
This guide covers the design-side process of creating an ECU pinout:
Not covered: Reading pinouts from an existing unknown ECU (that is reverse engineering).
When routing wires from the ECU to the engine, always leave 2-3 inches of extra wire length at the ECU connector. This "service loop" allows you to re-pin the connector 3-4 times if you change the design without building a whole new harness.
Connect CAN/LIN tool or laptop.