RS2 Overboost and surging issue

[Canadian RS2]

It’s possible you have a leak that doesn’t appear till pressure gets above 1 Bar, smoke is good but not as good as pressurising the inlet tract to 1.5Bar.
Otherwise yes, removing the cats can definitely cause overboost if a chipset is mapped near the limit. I had exactly this on my RS4 (also mapped by PRJ) when the stock exhaust was changed for a full Miltek without cats.
However, it would only overboost occasionally when I really slammed the throttle and then it would drop into limp mode.

Thanks Newsh.

I'll retest with pressure and see what happens. If it is being caused by the removal of the cats, would a Manual Boost Controller help limit the boost to 1.5 and stop the surging?

[newsh]

It’s possible you have a leak that doesn’t appear till pressure gets above 1 Bar, smoke is good but not as good as pressurising the inlet tract to 1.5Bar.
Otherwise yes, removing the cats can definitely cause overboost if a chipset is mapped near the limit. I had exactly this on my RS4 (also mapped by PRJ) when the stock exhaust was changed for a full Miltek without cats.
However, it would only overboost occasionally when I really slammed the throttle and then it would drop into limp mode.

[Canadian RS2]

I am experiencing an overboosting issue. The engine boosts strong to 1.5bar up to 2nd gear but once in 3rd it overboosts to 1.8 then cuts back to 1.5 and continues to surge up to 1.8 and back to 1.5 through 4th gear and up. I've replaced the N75 valve which fixed a problem I was having with the turbo fluttering but the surging problem persists. I smoke tested the vacuum lines and replaced a few vacuum hoses that were leaking. There does not appear to be any more boost leaks.

I've inspected the waste gate diaphragm and it looks fine.

The main change I've made is installing a turbo back Supersprint exhaust with a straight downpipe so the cats have been removed. Could this be causing the turbo to boost to quick for the ECU to respond? The RS2 is chipped with a set of PRJ chips.

Any ideas what the issue could be?

Thanks,
Dave