BOOST CONTROL SOLENOID - this is only on '89-91 Turbos. If you're at the point where you're removing the solenoid rack, your car is modified, and you need to ditch this anyhow - it will give you some serious overboosting problems. Remove it, and cap the hole on the turbo inlet duct and the nipple on the metal hard line that feeds the wastegate actuator.


thats from the write up in the archive on emissions removal..I was just curious how the silenoid causes over boost problems??

 

I don't know how much you know about these, so apologies if I cover stuff you alrteady know.

Electronic boost controllers (factory and aftermarket) work by using a solenoid valve to bleed pressure out of the wastegate actuator line, so the wastegate opens later. The amount of air bled out, and hence the boost achieved, is varied by pulsing the solenoid open and closed and varying the duty cycle (i.e. the open time per pulse). They also bring boost up quicker by leaving the solenoid open until just before the max boost setting. The ECU is programmed to start restricting the bleeding air at the right time to stop boost climbing and not overshoot.

When you remove airflow restrictions (intake and exhaust mods) the turbo is able to build boost quicker, but the ECU doesn't know this. It controls the solenoid like it always has, but now boost rises above the boost set-point before the system can react, and you get a boost spike. This is a common problem when modifying any car with factory electronic boost control.

Removing the solenoid will prevent this problem, but it will also dull boost response. You could replace it with an aftermarket EBC, but a much cheaper option is to add an adjustable restriction (a ball valve) in series with the solenoid like this:

http://us1.webpublications.com.au/st...8/1836_9mg.jpg

This allows you to tune out the spike. Here's the result on a WRX:

http://us1.webpublications.com.au/st.../1836_14mg.jpg