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Rb25det Neo not revving past 5k?

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Before anyone asks, yes i've done the usual searches but I couldnt find anything definitive :10_wink:

Background: Stock Rb25det NEO. standard intake, exhaust, boost and ecu.
Engine shuddering or hitting fuel cut whenever WOT and high boost (bucking like a mechanical bull), other than that, it ran fine. boosted down low ok, seems to run smooth(ish). didnt run rich, was getting on average about 450k's per tank
Replaced spark plugs with NGK coppers (1.1mm). Car then had absolutely no torque down low, would backfire constantly when cold or after WOT (which was necessary to get the friggin thing to move) and wouldn't rev over 5000rpm. It felt like it hit Rich and Retard. No codes were thrown

I noticed that the boost gauge was reading a little high after the plug change, and found a vacuum line from the charcoal canister had frayed and cracked causing a vacuum leak. Replaced this and boost reading went back to normal.

I then replaced the Airflow sensor (2nd hand from wreckers), Coilpacks (splitfires), Coilpack lead (Genuine) and Sparkplugs (NGK BKR6EIX-11).
This made a HUGE difference. the old coilpacks were likely from the factory and were just producing a weak spark.
Reset the ECU, still ran rich when cold (but not as rich), low-down torque came back but still cant rev over 5000rpm (feels like the engine just goes back to the R&R state)
It does backfire a little when cold or after WOT (more like a few pops instead of a full blown backfire). Still no codes thrown

Does the ECU lock out the top 2000 RPM when its 'learning'? or is it something else?

What should I be looking at next?
O2 Sensor?
Replace/check all Vacuum and Intake lines?
Cam angle sensor?

Really running out of ideas here

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Check fuel pressure.  Under load.

Also just maybe an outside chance that the ECU's water temperature sender is not right....or even the thermostat is stuffed and it's too cold.  Check that too if needed.

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you could have a boost leak under boost and its hitting the air flow cut.  block your bov and pressure test the system and search for leaks

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So this saga is still going on.
Taken it to two separate mechanics, both said that it 'seems' fine.. (despite the fact it cant even get close to the rev limiter in 2nd) 

Ran a boost leak test using my puny ryobi tyre inflator, it held 5psi for about 20 seconds which appears to be ok.. it seems that there's something else going on.
I've plugged in the consult cable and engine temps appear normal as far as i can tell.

Also appears that i'm running .75 bar of boost now (up from .5).
I changed the vac lines to and from the turbo and solenoid hoping that it was just a leaking line that was throwing everything off, still no joy (hiss/whistle noise cant be located with soap and water on any of the couplers)

I'm starting to think now, no power past a certain rev range + hiss/whistle noise + higher boost..  could it be an exhaust leak? or am i just reading too much into this?

Edited by lench

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