fuel pump dying??

[dubslug]

i got a mk2 8vgti pb engine code done 134000 miles

right my problem is this, a guy came out to tune the car as it had been running rough on idle etc, anyway he plugged all his stuff if and went to adjust the co mixture, say he set the level at 3%(dunnno the real number) and left it to idle the co went up to 7.5% than dropped back down to .5%, ive replaced the blue and black sensor on the front of engine, cleaned the isv(did the same with it disconnected to)... the guy says all my ignition side of things is spot on etc, so he thinks its fuel or ecu related.

Anyway my fuel pump is proper noisy all the time even after new lift pump and fuel filter, it buzzes real loud when priming but then buzzes abt half level all the time, sounds like i got an air leak in exhuast but hvent if u get wot i mean, also some mornings it sounds like its struggling to crank over, does this sound like main fuel pump failure???
also would that cause the co levels to change so much??

plz help guys as its nmy first gti and i wanna keep it lol

[free]

yeh it could b, ?but i dont no about the co levels changing

[dubslug]

im thinking maybe the pressue drops so the mixture becomes lean or rich if u get wot i mean??

[Gambit]

u need to check the fuel pressure properly. noise level doesnt determine fuel pressure.

my fuel pump is very noisy but its still providing perfect pressure

[dubslug]

how do i do that gambit??
how come it sounds like its stuggling to turn over sometimes??
cheers for replies ppl keep em coming

[Gambit]

you just get a pressure gauge and connect it between main fuel line coming from the tank to the fuel rail

is it the pump that struggles to prime or is it that the pump aint getting enough power to prime it, like a dirty itermittent connection?