We have found from working on all engines with an ECU (Electronic control Unit), sometimes referred to as an ECM (electronic control module), that the battery voltage is critical during start up.

as the starter motor is engaged, a large amount of current causes the battery voltage to drop and below certain levels, the ECU will fail to start the engine.

This seems to be a particular problem on large Cummins engines.

In order to solve this problem, it is essential that the battery is fully charged and that the appropriate sized leads are used to carry the current to the starter motor.