Hi Brains Trust, 
 
Been having this issue for a while. I have a 3S with a CT26 and Electronic Boost Controller and Fuel Cut Defender. 90% of the time it boosts perfectly and responds perfectly. But after I drive it hard and do some hard cornering and boosting the engine drops the psi of the turbo. It's likely pulling timing as the ECU has no control over the turbo as it go's through the EBC. What I want to know is why the hell its doing it. If I turn the car off and wait 5min it's fine so it's likely a sensor somewhere not doing what it should. I'm not getting any CEL lights so no codes to check. If someone can suggest an idea or provide me with a list of sensors I should replace please provide this. Any help is welcome at this point. 

Normally with the EBC at no settings the stock boost is 12.5 but when this issue happens it reduces to 7psi and just feels like someones taken over the throttle and lowering it.

If you are still on the OEM ECU it is probably detecting detonation and doing exactly what it's meant to do and pulling timing to safeguard the engine.

If the knock sensor was picking up detonation then that would cause a CEL light though, wouldn't it?
 

You would expect it would. BUT. Not always.
Cold dense morning air. A fair old bit of boot into it in third gear and it would no longer boost at all.
Drove gently just fine. I'm crapping myself. After a couple of minutes it came back as though nothing had happened.
No CEL at all. Boosts to 15 PSI just fine. Sometimes on the track when I'm giving it what for it will kinda go off song and it will chuck a CEL. No apparent reason but I assume it's detecting detonation. It's a Gen 3 with OEM ECU and a bit better turbo than stock. Hopefully someone with way more experience than me will come in on this topic.

What condition is your turbo charger in? I've had the same symptoms in a friend car, ended up being a worn seals in his turbo from memory. I'm sure there are other like reasons.

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I've never really had the issue on cold mornings. If anything its when the engine is hot. Could be detonation but I hope it isn't.
 
I actually hope its the turbo because I have a CT20b ready to go on. The existing CT26 turbo has done 270,000k's so it's probably time for the upgrade. The only thing that bugs me is, wouldn't the problem be consistent if it was turbo related? This is why I think it's a faulty sensor or some electrical gremlin. 

i fail to see how even if the ecu has detected detonation and retarded timing that the boost pressure would be dropped, the turbo will still boost to what the ebc is set to.   

These were my thoughts as well the turbo is not monitored by the ECU anymore. But it gets killed by something in the engine which I assume is it pulling timing given there's little else it could do that would reduce boost pressure. 

timing retardation doesn't reduce the amount of boost from the turbo.