Hi Colin, i done a Caddy not long ago it turned out to be the o ring seals around the injectors VW do a kit for these which includes a new set screw for the injector about £18 per injector.

As Mark said you are checking the cavity pressure not the pre supply pressure the one i done had about 2 bar cranking after about 20 secs of cranking when i replaced the seals it fired up instantly and run about 4 bar

be careful setting the injectors up when you replace the seals there is a procedure to follow
if you don't you could damage the injector

And they are about £400 a pop

hth

Kev Gundry