lack of boost

[add]

Well,once again i've got boost issues,the car seems ok up until around 4000rpm when it just seems to go flat with very little boost at all,it's not cutting boost as i've had that before and it nearly puts you through the window.it almost seems like the turbo has dissapeared from 4000rpm onwards under heavy acceleration.
I'ts had a new maf,and recently been given a once over following the previous boost leak i had-does this sound like a familiar problem to anybody?
Any help greatly appreciated as it's really annoying-i struggled to over take a vauxhall corsa!-nuff said

[HPmuirt]

Need more info such as: -
- Have you got any fault codes
- What the boost gauge shows
- Does it reach full boost at 3000rpm and them just fall off
- Can it boost above 0.4 bar (or is it in limphome mode)

Most likely it's airleak or the WGFV but lost of folks are having issues with the MAF connector at the moment. I have a hesitation at 4000rpm which is known to be my Lamda sensor hence asking about your fault codes.

Cheers n

Si

[add]

thanks for the reply,
I havent retrieved any fault codes as yet but i will be plugging into it at somepoint,unfortunately i don't have a boost guage as yet so i can't tell what it's boosting to ,although below 4000rpm seems ok, after that it just falls off boost quite quickly,i don't think i'ts in limphome mode as it doesn't seem too bad if driving normally,
i forgot to mention that it's had a new lambda sensor so that's ok-although it has been chipped,by whom i don't know but maybe this could be causing the problem-it runs quite rich so i don't think theyre well suited to the car,i've ordered a new wgfv today as the old one looks ancient to be sure-it just seems strange how this has happened all of a sudden