Tuning problem - any ideas?

[fullahotair]

A friend of mine has a 84 GN and is experiencing some tuning issues. I haven’t seen the car personally or experienced the problem, but over the phone he has told me that the car kind of pops/misses at the top end with the pedal floored. He then gets a Code 31 which is a waste gate issue. He has installed a bigger fuel pump, modified the stock fuel regulator for higher fuel pressure, new plugs/wires, and has performed an 86/87 coil conversion. He doesn’t have a scan tool yet or have a knock sensor, so I understand the info is limited, but I was wondering if any of you guys could offer some insight/advice based on what we know.

I told him that the first thing to do is to get a scan tool and some guages to know exactly what is going on, but I thought maybe someone here could help out.

Thanks,
Nathyn