turbo problems?

[mattman]

hi again my bros astina has been running strong on 13 psi for a while now but today it started playing up when it gets to about 4g it would hold back and mis and wont go any higher (its not boost cut i know what that feels lik)so we downed the boost to stock and droped the fuel pressure down to 40psi and it drives alot beter but at 4g it would hold back a tiny bit but you can rev it right out im stumped

any ideas

cheers matt

[NaughtyGT]

Well that sounds like a spark problem. Have you stock dizzy & cap or are you running coil packs? Firstly, check leads & cap/coils for anything that may be exposed that is possibly shorting. Replace leads if they are old or your not sure of their age? It may also be the coil packs if your running them.

Start trouble shooting with ignition system first. Failing that, check the fuel system