Pulsed injectors on/off times

[Paul Nicholson]

At 5:19 +0100 2/12/01, Jorgen Karlsson wrote:

>There is a simple way to measure the time it takes for the injector to open.
>A signal generator an oscilloscope, a .1ohm power resistor and a drive
>circuit is needed to do this. Using a car running at idle works.

Results will vary depending on the drive circuit and voltage. The opening time dependent on the current and the rise time of the current is dependent on the voltage. The closing time is also important, as this can vary according to the drive current (some circuits switch to a lower hold currents once the injector is open) and the load dump circuit.

>Connect the resistor in series with the injector, measure the voltage over
>the resistor with the oscilloscope, when you have got it to trigger
>correctly you will have the shape of the current on the display. It will
>increase rapidly at the beginning and then start to stabilize. Then at a
>well defined point the current will start to increase quicker again, this is
>the point where the pintle bottoms out, the injector is fully open.

If you vary the pulse width, you can easily hear when it gets wide enough to open the injector. Jorgen is right about the current wave form. There's a vary pronounced discontinuity in the current when the injector opens. You'll both hear it with your ears and see it on the scope.

Paul