Fuel Injector polarity

[gordon54]

I see that most all MPI fuel injectors have a "+" polarity marking on them.
We have measured the injector "on times" using an accelerometer and don't see any difference in operating times with either polarity.
I'm sure it is there for a reason.... Who can enlighten me?

 

[ufe777]

I'm not familiar with the internals of injectors but perhaps it has an inbuilt Diode to supress voltage spikes when the magnetic field in the solenoid coil collapses?

 

[dgallup]

I have been testing and designing electronic fuel injectors for more than two decades and have yet to figure out why Bosch and some others indicate polarity. There is nothing but a coil inside conventional electromagnetic injectors. I have done extensive magnetic testing and there is a small difference the shape of the first pulse when you reverse polarity due to hysterisis. Any trace of this is gone by the 3rd pulse so it is insignificant.

There is a significant back EMF when the magnetic field collapses but this is absorbed by either an RC or (more commonly) zener circuit in the ECU. The breakdown voltage of the insulation is typically more than an order of magnitude higher than the back EMF voltage.

Siemens, Delphi, ourselves and many others do not indicate polarity.

 

[schmidtj86]

Maybe it's so that people don't ask "does it matter which way I connect the wires on the injector?" If you just tell them one way is right, with a simple mark, it may save a lot of emails and phone calls, and wasted time.

 

[turbocohen]

The mark allows a technician to match the terminal polarity to the terminal of the harness.. helpful for diagnostics.