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Fuel System

Does fuel injector polarity matter?

Cummins X12 Injector
Some engine manufacturers such as Cummins, use injectors without connector plugs or with unmarked terminals. If this is the case, how should we connect the cables on the injector? Will the ECU show injector faults if we reverse the polarity? Does injector polarity matter?

Fuel injectors operate on a very simple principle: electromagnetism.

In any type of solenoid-based injector, we will typically find the following components:

  1. A coil
  2. A plunger or needle made of metal

The plunger or needle (depends on the injector type) is held down by a spring and closes the injector outlet. This “traps” the fuel inside the injector body and allows for pressure to accumulate.

For injection to start, the plunger or needle has to lift and allow fuel to escape through the injector orifice.

The whole process is controlled by the ECU, which at the right time provides Voltage to the coil. The Voltage creates Current flow (Amperes), which in turn creates a magnetic field around the coil.

The plunger or needle is attracted by the magnetic field and as long as the magnetic field is stronger than the spring’s force, the plunger or needle remains lifted which allows fuel under pressure to be injected.


Does fuel injector polarity matter?

No it doesn’t. The metalic plunger or needle of an injector will always be attracted by a magnetic field, regardless of the field’s polarity (North or South).

So, even if the coil’s polarity was reversed, the only thing that would be affected, would be the polarity of the magnetic field.


Post author
Picture of George Sarimpalidis

George Sarimpalidis

I've got a long experience as technical trainer and training course developer. My specialization is diesel engines and electronic management systems. I love learning about how everything works and then explaining complex systems in a way that everybody understands. The more complex, the better!

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