I tapped a couple of LEDs into the front and rear diff solenoids (at the start of the FDCM loom.), to get an idea of the QDII behaviour (when it locks and unlocks each diff, the duty cycle, etc.).

Pin #14 (Dark Green / Yellow) is constant +12V. Pin #22 (Dark Green / Dark Blue) is the front solenoid control. Pin #23 (Yellow / Violet) is the rear solenoid control. Both #22 and #23 are +0-12V and appear to be 1KHz PWM, so you can think of them as a variable ground (as far as the LEDs are concerned.).

If it proves useful as a driving aid (like knowing when clutch-pack pressure has been released before making a sharp turn at a switch-back.), I’ll mount them a bit more neatly - Probably just embed them within the ScanGauge like I did with the MDS activation LED.

The points demonstrated in the video (which are annotated) are;

  • In high-range, front and rear solenoids activate after some spin, but deactivate immediately after backing-off throttle. Therefore, front and rear diffs will "lock" in high-range, providing that you stay on the throttle.
  • The solenoids will activate even if there is no pressure available to "lock" the diffs. The diffs are primed with pressure by the gerotor pump (through differential action; turning, spinning one wheel, etc.). So if you've been driving casually along a straight road, immediately enter low-range and drive straight (without much turning.) into a cross-axle or low-traction situation, it'll take a little bit of wheel spin until the diffs "lock" and get you moving.
  • In low-range, the solenoids remain active (diffs "locked", assuming there's enough pressure.) for some time after releasing throttle and traction is regained.
  • When the diffs are primed with pressure, they "lock" pretty-much immediately when the solenoids activate. This is the main improvement in QDII over QDI. QDI diffs don't have a solenoid to control when pressure is applied to the clutch pack, so the pressure is always "applied" (with some bleed off you'd presume.). Thus, QDI effectively always requires a bit of wheel-spin before "locking", and will also always "lock" slightly during normal driving (sharp turns in car-parks, etc.) - Which is probably why QDI diffs seem to suffer more from incorrect oil or friction modifier.
  • The solenoids deactivate immediately when returning to high-range.

The main conclusions I take from all that are; take it easy with any sharp turns immediately after the diffs have “locked” (just to minimise wind-up, you might consider shifting to high-range temporarily to force the diffs to “unlock” in some situations.). And don’t be too quick to return to high-range when driving a road/trail with varying conditions… if you remain in low-range, the diffs are more-likely to be primed with pressure and thus lock immediately when you need them, avoiding excess wheel-spin.

There might also be some interesting discussion where I’ve posted this on the AJOR forums.