Solenoids were applied to fuel injection in 1913. To this day, physics still limits their force and speed.

Relatively weak and slow, the solenoid is confined to operating a servo valve in the injector. The solenoid and servo valve cause significant, and now unacceptable, time delays.
  • The servo valve directs fuel pressure to operate the injector needle. Finite time is required for a pressure wave to propagate through the fuel between the servo valve and needle.
Very finely tuned for some speed, operation is then sensitive to fuel properties.