I am having an issue that I thought I had once resolved. I recently purchased a low mileage garage kept 03 Vitara. After troubleshooting the lack of a 4x4 light, I discovered the pump was not working while also determined that the front diff was holding vacuum (in lieu of pressure). I repaired the pump on the bench and replaced some hoses, the 4x4 light came on and the wheels engaged while on my lift as they should. Forward a few weeks and I am pulling a small bush out in our yard (on loose gravel) and only one rear wheel spins. 4x4 light is on as normal but no engagement of front wheels. On the lift again this morning and the diff checks out with vacuum, the light is on, but no engagement. This time I put a low pressure gage on the hose at the front diff and it is getting the required 5 psi. So the diff holds vac, and the pump puts out. Any experience with this out there? thx

Update; I applied regulated shop pressure to the diff. 9 psi actuated the diff and engaged the wheels. The pump cycles off at 5 psi and is the normal pressure switch pressure setting as for as I recall. It was initially actuating at 5psi when I first repaired the pump, now it seems it is inefficient. No changes other than I recently changed the diff oil, using Lucas 75W-90. Still puzzled.