Ca18det wont hold boost?

Hi!

I've got an odd problem and I'm stumped on what to do. Fully built engine with stage 3 and s15 bb turbo. been running 1,5bar previously without any problems.

When driving under load the car will boost fine up to about 1 bar and then the boost vanishes but the car will continue to rev all the way up, but as if it has 40hp.
If i let go off the throttle after the boost disappear it will do the same thing again, just higher up the revs. Driving the car under 1 bar it works fine.

I've checked all the pipes and hoses and can't find any leaks. No bubbles.
Tried removing the bypass valve incase it was malfunctioning, no difference.
Tried removing the controller (manual screw type) still the same.
Checked the coilpacks and plugs
AFM works and is clean (z32)
Removed fuel filter in case it was jammed
redid the earth to engine, battery, fuel pump and harness

I dont know what to try next really, has anyone had these problems before or got a good idea of what to look for?

Thanks

It’s a boost leak.

Pressurize your piping to 2 bar and you’ll see where its leaking from


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Boost leak, Vac leak or a broken actuator are most likely.

It sounds like your wastegate is opening on the turbo. To suddenly lose 1.5bar, and it not sound like a dump valve venting, it has to be more than just a loose pipework clip.
Have you tried removing the vacuum line to the actuator? (Obviously be very careful you don't over boost) It might highlight something.

1.5bar on a t28r??? Surely you're just blowing hot area at that pressure!
1.4bar is about happy on a 2871r.

Sorry off topic but you'll have bigger issues if you start detonating at 1.5bar