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Discussion Starter #1 (Edited)
magik8 said:
This is a common misconception and really needs to be clarified as it seems people still don't understand what the stock boost solenoid is for. The stock boost control solenoid does not work like a Manual Boost Controller (MBC). It is completely different and is used for a diffrent purpose than an MBC. The purpose of the stock boost control solenoid is to allow the ECU to put the turbo in "low boost" mode when the ECU sees knocking.

When the stock boost control solenoid is open (normal condition, 99.9% of the time), the air pressure coming from the compressor and reaching the wastegate is divided between the solenoid-to-intake hose, and the solenoid-to-wastegate hose. The stock boost control solenoid is only closed when the ECU sees detonation (knocking) from the knock sensor. When the solenoid is closed (should be a rare occurrence), the solenoid-to-intake air hose is closed off and the full pressure from the compressor reaches the wastegate, opening it earlier and hence regulating boost to a lower level.

An MBC works completely differently in that it "intercepts" the air pressure from the compressor, and allows it to reach the wastegate after it reaches a certain pressure. The stock "boost control" solenoid does not work like this in any way, shape, or form. It does not close off the air to the wastegate under any circumstances.

If you read this over a few times and think about it, you'll realize that your stock boost solenoid cannot be used as an MBC. Stock boost solenoid has three vacuum line connections. an MBC has two.

The actual test according to the shop manual:

Disconnect small air tube from air hose (the one underneath)
Disconnect the solenoid wiring and blow through the bottom hose. Check that air does not move. (0% Duty Cycle)

Apply 12v to the solenoid. (100% Duty Cycle)

(the way it's described in the manual is with the plugs tang at the top, the lead on the right would be + and the one on the left would be ground)

Blow through air tube and see that air passes.

It looks like this:

With 12v applied, all ports are open and pressure is divided between the three nipples. When voltage is cut, the bottom nipple closes leaving boost pressure to come through the L shaped nipple in front, through the solenoid, and exiting through the rear nipple l on its way to the wastegate. This gives the wastegate full pressure from the turbo and will lower the boost pressure up to 2.2 psi with a fully functional wastegate actuator that is working properly. The ECU of course has the capabilty to retard timing up to 6º depending on load as well.

Meaning that above 4,500 rpm, duty value will change to lesser voltage on the solenoid (lowering boost) as you approach redline.

Here we see that the duty value is 100% (fully open) under warm and cold conditions, under medium load. Value changes during acceleration as well as under heavy load (when knocking occurs) and is controlled by boost pressure.

Scan from Magik8:

And stock boost solenoid discussion:

I think this should pretty much clear everything up.

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