Injector dry firing?

[Craighell]

During a test session inside the trailer, our injectors lock up (at least make a drastic change in sound) at any opening event requiring more than 15.7 m-sec PW. ~85% duty cycle. The test is very short taking less than 30 seconds to complete, but I wonder if that matters.

Note there was no fuel being supplied to the injectors and I am curious if this totally invalidated the test. I understand that the fuel pressure will tend to help close the injectors, that seems straight forward, but what is the effect?

Thanks
Craig

 

[schmidtj86]

I know I wouldn't put my injectors through much testing without fuel going through them at high duty cycles, but it shouldn't kill them, unless you hold them static (100% duty cycle).
What kind of injector are they: Peak and Hold (low impedance) or Saturation (high impedance)? And are you sure they are the right type for the injector drivers in the ECU?

How are you measuring duty cycle? With an Oscilloscope (right way) or by looking at the fuel injection system's output of pulsewidth?
Why are you dry testing them anyway?
Hopefully you can put an oscilloscope on the driver side and see if they are going static, even if the fuel injection software says they aren't.
I would check that and see what is actually going on.

 

[jons999]

I think your best bet would be to run some fuel through them, even at low pressure, when you test them since the fuel lubricates and cools the injectors. Running them dry could heat them up and change the resistance of the coils, making your test results very inaccurate. Theres also the possiblity that you could burn out the injectors dry firing them, but thats unlikely in that short of a test.

-Jon

 

[Craighell]

Thanks for the replies guys,

The folks at BDS said I shouldn't have a problem with the dry fire mode provided the test duration was short.

Turns out we were not really at 85% Duty Cycle. Opening time and closing time was really eating up the cycle and we were on the edge of static.

Ouch!