Turbo spooling waaaaaay high!, need boost to come down......how?????? Options

[injection]

Hello doctors, get your surgical gloves on, because i need help.....
i have asked this question before with no solutions, so i will try again, maybe someone will pick up something i missed, hopefully!!!!!
basically, my 94 celica gt, which i swapped a st205 into, was up and running last may ( 2011 ), ever since then, my boost climbs to around 19-20psi, i have hit fuel cut twice, and smacked my face into the windshield the first time ( seatbelt safety ),
anyways, in order to stop hitting fuel cut, i have to let off around 5500-5700rpms, because im right on 18psi, and dont want to keep hitting fuel cut....cant be good
so heres what ive trouble shooted so far:
hooked air compressor up to wastegate with 15psi pressure....opened perfectly, quickly and smoothly
have an XS Power DP, checked to make sure the actuator clears the DP flange....it does
there is a line that comes off the wastegate and goes behind the bottom of the intake manifold to a sensor called a VSV valve???? i think its called, anyways, hoses are hooked to that and return up front, cant remember where the line goes up front though??
thats about it, kinda outta ideas

I was thinking of purchasing a manuel boost controller, but isnt that for turning up boost, or can you turn down boost as well ( explain please )
If that doesnt work....is there some sort of a bleeder type valve i can buy, to vent some pressure, or does that screw-up vaccum

Thanx, hope one or alot of you have an answer to my problem 6GC

[3WayStunna]

Wow zombie thread. Lol might as well as add my .02. Just wanted to add to the debate on how (and to be specific) an AVCR can lower and control boost pressure when experiencing boost creep. Just to note this is just me speaking from my experience. Not trying to stomp on ideas or promote APEXi's products.

I think the problem can be solved with an ELECTRONIC boost controller. And here is why i think that. The stock boost controller is the VSV. Basically a bleed valve. When the BCS (Boost Control Solenoid) senses an overboost problem, the ECU sends a signal to the VSV ( Vacuum sensing Valve) basically putting the turbo in the mode we all know best (boost cut/fuel cut etc.).

How this works is once the BCS sends the signal to the ECU, the ECU de-engergizes the VSV allowing bleed air to leak from the waste-gate. This works well on the stock setup but as we start to add more and more then we would likewise have to upgrade our controls to the stock system as well. How an electronic boost controller (specifically the AVCR) works is by getting rid of the stock boost controller system all together, in a manner that a manual controller cant do.

It does this by

1:) Altering the boost signals to the ecu by having them go to the AVCR first
2:) Getting rid of the VSV system completely in a manner that im sure many manual boost controllers would do
3:) Using a faster acting solenoid than can more quickly handle the amount of boost the AVCR is picking up from the BCS
4:) Fine tuning, fine tuning, fine tuning.
5:) Using an electronically controlled solenoid

You will still experience boost cut though, but you would be able to fine tune out the boost creep or just simply set a lower boost IE: .9-1.0 bar, for example.
Now im not saying that any of the other ideas wouldn't work and hopefully not beating on a dead horse. Its just the the original poster said he isnt in it to add an external waste-gate, which would also work (not sure on how well with the stock ecu), and adding restricter plates etc. IMHO is just too much for a problem with an obviously simple solution.

The only way to get rid of the boost cut btw is either through an after market ECU or FUEL CUT DEFENDER of some sort (make your own or buy one).

Also some reading, in case terms are lost on some folks.

http://www.celicahobby.com/forums/ubbthrea...ite_id/1#import

THE TURBOCHARGER
The turbocharger is a centrifugal compressor driven by the otherwise-wasted energy in the exhaust stream. It is a 2 chambered housing with a shaft through the center extending into both chambers. A turbine wheel is mounted on one end of the shaft and is in the exhaust stream, and an impeller wheel is mounted on the other end. That is the compressor end, and it is connected to tubing that goes to the intercooler, and then to the throttle body. A turbocharger is really a very simple device, and as long is it regularly fed clean , high quality oil from the engine lube system, and allowed to cool down before engine shutdown, will last nearly as long the engine itself.

THE WASTEGATE
There are two alternate paths for the exhaust flow at the turbo. One is across the turbine, and the other is out the wastegate, allowing it to bypass the turbo. Since more energy at the turbo means more air to the engine, which means more energy to the turbo, which in turn means more air to the engine, which means...well, I think you get the point. The wastegate is necessary to limit the airflow output from the turbo.
The wastegate isn't simply open or closed; it modulates to maintain very precise control over the turbo's speed and output.

SOME BASIC PHYSICS
Compressors are pumps, and pumps create flow. When the turbo creates more airflow than the engine is consuming, then the air becomes pressurized. So boost pressure will rise and fall as the turbo output increases and decreases. Thats why the wastegte controls the speed and airflow of the turbo. And pressure and flow are directly related. That means you can not get "more flow at the same pressure..."

THE WASTEGATE ACUTATOR
The wastegate actuator is simply a can with a rubber diaphragm on one end, and 2 ports with hose fittings on the front end. Looking into the engine compartment form the driver's side, it can easily be seen just to the right of the turbo compressor inlet. The hose on the left is connected to the turbo, and the hose on the right is connected to the T/VSV. (more on that later) There is a spring that holds the diaphragm in place that has a yeild value of about 7 psi.. As pressure builds in the turbo, air begins to fill the actuator and pushes against the diaphragm. When the pressure exceeds the spring value, ~ 7 psi, the actuator moves out, pushing a rod, and opening the wastegate.

TVSV
(Turbocharger Vacuum Switching Valve) is a "factory-installed boost controller". It is simply a solenoid-operated valve that, when energized (open) allows air to escape from the actuator, lowering the pressure in the actuator, and allowing the wastegate to modulate closed. This vented air actually flows back into the intake airstream between the airflow meter and the turbo intake so it does not distort the ECU's air/fuel ratio calculations.

The T/VSV is a normally closed-energized open valve. The ECU will energize (open) it whenever you boost IF 1) engine coolant temps are up to normal , and 2) ambient (intake) air temps are above ~ 32 deg F. (There may be some variation with that number). If the T/VSV is open (high boost mode) and the ECU gets a signal from the knock sensor, it will de-energize (close) the T/VSV. Likewise, if there is an over boost signal from the boost pressure sensor, it will de-energize the T/VSV as part of the "fuel-cut" sequence.

NOTE: Unless you have an aftermarket boost controller, disabling the T/VSV will lock you into low-boost mode!! It WILL NOT increase boost.

The normal range of max boost ranges from 7.1 to 11.8 psi, according to the Factory Repair Manual. Low boost problems are almost always a result of some problem in the boost control system and rarely with the turbo itself..

BOOST PRESSURE SENSOR AND FUEL-CUT
The boost pressure sensor is simply a pressure transducer that monitors manifold pressure and reports it to the ECU as a voltage value. If the voltage exceeds about 4.4 volts (~12 psi on '91, 92' and early 93's, ~16 psi on late 93's and up) the ECU initiates the fuel-cut sequence. It de-energizes the T/VSV to lower boost, retards ignition timing, and restricts fuel delivery by limiting the injector cycle. The "check-engine" light will come on for about 20 seconds, and a code 34 will be stored in the diagnostic memory. You will be in "limp mode" and unable to boost again until you shut off the engine and restart it. No other reset is required to return to normal operation. You do not have to pull any fuses or disconnect the battery (Internet legend!)

For a complete schematic diagram of the turbo and boost control system, go here:
http://member.newsguy.com/~gtfour/technicl.htm#Turbo
Click on "Boost Control"

This post has been edited by 3WayStunna: Apr 9, 2012 - 9:30 AM