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lench

Overboosting on Wastegate pressure - (almost) Stock RB25det neo

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So I've been chasing problems for a while now, but this one has me at a dead end.
Either way, I've currently got my car running on wastegate pressure (vacuum line from turbo outlet to wastegate actuator, bottom pipe has been plugged up) so i'm running .5bar steady, but when it gets to around 4500-5000, the boost spikes suddenly to to 1 bar.

Currently running:

Stock turbo.
Stock wastegate actuator.
Stock Intercooler.
Stock Bov/recirc valve
Brand new 3" exhaust (but was doing the same thing on the original stock exhaust, just at .75bar instead of 1 bar, pretty much running on R&R)
All vacuum lines pre-throttle body and recirc/BOV have been replaced.
(essentially a stock car minus the exhaust)

I've checked for boost and exhaust leaks, which is another dead-end
Anyone have any ideas on what to try next? 

 

Edited by lench

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disconnect wastegate and check flapper operation on turbo housing. If it doesn't open and close smoothly by hand, could possibly be the issue. Would be a good place to start anyways.

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thanks, i'll give that a go tonight!

I've also pumped some compressed air into the actuator, it starts to move at 5psi, fully open by 14psi (tested it to 20) seemed to move ok, but i'll check the flapper as well

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RB25 wastegate pressure is 5 psi.  Only gets to 7 by the action of the stock bleeder solenoid.  Should be all open way before 10 psi.  I suspect that there is something sticky/bent/broken.

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is your CAS fully retarded?

I've had cars with aftermarket turbos stock actuators shoot up to 1.4bar 1.5bar of boost when timing is super retarded (CAS off by 10~15 degrees). Happened last week actually, was doing some basic street tuning before the dyno next week and the car kept shooting above targetted boost.

Checked the CAS again and it was off by about 15 degrees lol.

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not heaps experienced with this, but i've had a mech put the timing light on it and told me it was fine
ran ECUtalk with the consult cable and it seems that the timing is between 11 and 15 BTDC on idle

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16 minutes ago, lench said:

not heaps experienced with this, but i've had a mech put the timing light on it and told me it was fine
ran ECUtalk with the consult cable and it seems that the timing is between 11 and 15 BTDC on idle

ECU might think it's whatever you saw on the ECUtalk, but is it synchronised with the motor?

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Can't 100% confirm that, but my mechanic said it was within in spec with what the service manual says (guessing 15 degrees?)

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