Jimbob

iTrader: (13)

Hi as above really what is the pressure that [if there was no controller and the pipe from the turbo was fitted directly to the wastegate actuator] would the wastegate open??

This is a MY 1995 WRX JDM, Z4 ECU, from what I can gather it should be 0.5 bar so 7psi that the waste gate opens??

Reason I`m asking is mine is boosting to 9psi then boost cut (feel it would like to carry on tbh), this is with the pipe from the turbine plumbed directly to the wastegate actuator.

I`m just checking this is wrong and I`m assuming the plan to solve would be to unwind the actuator arm until I achieve 7psi MAX, as at the moment it hits 7psi and then builds steadily to 9psi where she cuts, but feels like the pressure is building still and if the boost cut didn`t come in the pressure would exceed 9psi.

saiklon

Wastegate opening pressure is usually 0.4 to 0.5psi depending on how preloaded (shortened) the wastegate arm is.
Loosening the wastegate arm would reduce the pressure down from the current 9psi you are getting.

However the symptoms you are describing probably point to another problem. On the Z4, boost cut is at ~16psi, so there's no way you are getting close to it at 9psi, maybe you've got a faulty MAP sensor? Tried checking for engine fault codes?

Jimbob

iTrader: (13)

No codes at all, but speedo cable not the greatest.

To describe, if I plant it and do short bursts of speed like driving in lanes, then no problems what so ever, BUT as soon as the road opens up and I start to build speed up it cuts but a small bit, then allows you build it back up.
Its on prolonged boost tbh.

Its strange.

saiklon

Cuts back a small bit does not sound like the boost fuel cut. That cut is a total cut, it almost feels like the engine is switched off, till you get off the accelerator pedal.

Is the cutting back RPM related as well? And can you describe it in more detail?

Jimbob

iTrader: (13)

Solved now (so far so good anyways), un wound my actuator arm and she boosts fully now, if anything the arm is a half a turn too loose as now I have a rattle from the wastegate pluggy thing. Have re-plumbed in the boost control solenoid and shes lovely, what I think I was getting was boost spike, as the waste gate wasn`t opening when it should, so when under boost she was producing too much so cutting.

Mind you I also changed the injector loom when I un wound the actuator arm so whether that the root cause I dunno, time will tell I suppose. But will deffo be winding in another half turn to stop the rattle as its doing it at idle and then a lot louder at cruise, so must be that (wasn`t there before). And now she will allow me to put the accelerator fully down and hold it down (boosts to steady 12-13psi), where as if I did this before she`d have some form of cut, where the engine would almost turn off as you say.

saiklon

I think that if you have to loosen the actuator arm that much to prevent boost cut, you have an issue with your wastegate actuator. I remember you said that the wastegate actuator is connected directly to the turbo outlet, you should not be getting more than 7psi with that, much less boost cut.

Try pumping some air into the actuator hose to see if the wategate arm moves, or if the diaphragm is really worn out, you might be able to blow through it.