mmmh i had a gander on clubgti and there was athread where a guy had changed his injectors, but the new injectors did not have the silver 'caps' on them, so he swapped them them over from the old ones, but it turns out the bosch techy he took it to removed 'caps' and car ran fine
have a look over on clubgti and do search of 16v fuelling
really you need pressure guage to diagnose fault otherwise its gonna be very hit and miss, oh and try a brand new fuel filter in case other one has been partially blocked