Water won't go in!

[nutron]

I've fitted two aquamist kits now, one to a 2.0 common rail diesel Mondeo (which work perfectly) and the other to my 1.9CDTI Vectra. As I say, the Mondeo had no problems and worked wonderfully; the Vectra is being somewhat of a pain though. The only difference I can see between the kits is the pump, the both claim to be the race pump, min 100psi. The Mondeo had quick release fittings though and the Vectra one has a quick release output but screw grip inlet. This doesn't seem relevant though as the pump is directly below the tank and there is no cavitation in the feed line (so far as I can tell).

The facts -

The inlet air pressure on the road peeks at about 30psi, on the rolling road though under less load it makes a little over 26psi.

I've hooked the race pump upto the same pressure sensor while running the car on the rollers and recorded 109psi.

The problem -

When the car revs up the fluid starts to move the wrong way down the tube then stops, as if the manifold pressure was pushing it back until the pump comes on. The fluid then stays there, rather than flowing back to the nossel and injecting. It was suggested that air might be being force back down to the pump and causing air lock. So I fitted a Halfords washer pump non-return valve just before nossel to try and prevent this but it's still not injecting.

I've tried the pump and nossel into air and they mist fine. I tried turning the pressure sensor right down to come in at about 8psi and I think it does come on because the car displayed some rough running at low revs (turned it off quickly). I've increased the nossel to a 0.7mm orifice and still nothing, so I'm now out of ideas. I can't understand how 109psi can be overcome by 26psi...

The pressure sensor is placed just after the intercooler and the nossel closer to the intake.
The pump sits directly below the washer tank and the pressure line feeds up (about 500mm to a custom made alloy pipe)
The nossel is in the bend at 90 deg to the air flow and sits flush with the interia surface.

I would love to know what's wrong as I now have 50 ltrs of methanol doing nothing and I want to have it sorted before Santa Pod reopens to improve on my 15.1 from last year.