Valve Controls and Automation

We currently have a problem of loosing lots of downtime in one of our Product Filling Machine. If we get underfilled bottle, we kind of struggling to find a fault quicker. We 120 Filling valves and each has a bank of solenoids: Vacuum solenoid, return gas solenoid and pretension solenoid. So when we have underfills on certain valve we first change the probes(filling/level); if the problem is still there then we swop the valves, if the problem moves with the valve, we then replace the valve with a spare unit. But if the problem doesn't move we then change the solenoids. The procedure takes bout 45 to 50 min. We therefore lose lots of time considering that we have to drop all the product to drain as we cannot remove the solenoids while there is still product on the bowl, it's sprays all over (that's another problem we having). I was thinking of installing pressure switches for each solenoid bank to monitor the pressure from each solenoid but it's very costly as we have 360 solenoids all together. Each bank is controlled by an interface card and the bank consists of 24 solenoids that operates on 8 valves and each valve has 3 solenoids (vacuum solenoid, return gas solenoid and pretension solenoid). Is there a better way of trouble shooting that will pin-point whether it's the solenoid or valve that is a problem or the probe, because the total downtime we get is about an hour considering start-up. Any ideas or quicker solutions? I'm prepared to spend on my budjet for extra installations or modification.