Boost issues

[Jesubi11]

So I have an 04 wrx wagon with 107000 miles on it. The only relevant mod is an V2 ap.
The problem is a lack of boost. I never reach over 8.5-9.5 psi. Also when I disconnect the boost control pressure line I still only achieve the 8.5-9.5 psi range. I have reset the ecu (several times) and still no difference. What I don't get is why disconnecting the pressure line would not make it build pressure like crazy. I'm under the impression that the default position for the waste gate is sealed, and that when actuating it opens. So why then would it not build pressure when it sees no pressure. Also I'm fairly certain that it is not stuck in the open position because of the position of the actuator arm. It is in the default position. My only thought is that the waste gate itself is cracked or gone, or maybe I have a crack in my turbo that just lets it through. Am I just being dumb and overlooking something simple. Any input would be greatly appreciated as the only thing left I can think of is to pull the stupid thing out. I almost forgot the ap says that my waste gate is actuating both the same with and without the pressure line connected.

Jeremy

[100_Percent_Juice]

I have 80,xxx miles on mine and my boost control solenoid went out not too long ago. I tested it by taking mine out and swapping it with my friends. Takes about 10min to do.

[kidatari]

Psst... disconnecting the wastegate line reverts to 'wastegate boost' which it typically set low to prevent the motor from self-destructing in case of the pressure line getting disconnected. That would be why it stayed around 9psi when you disconnected the vacuum line.

I'd wager that Mr. Juice is heading the right direction with the boost control solenoid.

[knucklesplitter]

Originally Posted by kidatari

Psst... disconnecting the wastegate line reverts to 'wastegate boost' which it typically set low to prevent the motor from self-destructing in case of the pressure line getting disconnected. That would be why it stayed around 9psi when you disconnected the vacuum line.

Psst... Not true. If you disconnect the pressure line or the line going to the wastegate then the wastegate will not open until pre-turbo *exhaust* pressure gets very high. Overboost will occur before that happens.

If you disconnect the line going to the the boost solenoid (and plug it), then the turbo reverts to wastegate pressure. (This assumes stock bleeder-type boost control).

Jesubi11, which line did you disconnect?

[Jesubi11]

Originally Posted by knucklesplitter

Psst... Not true. If you disconnect the pressure line or the line going to the wastegate then the wastegate will not open until pre-turbo *exhaust* pressure gets very high. Overboost will occur before that happens.

If you disconnect the line going to the the boost solenoid (and plug it), then the turbo reverts to wastegate pressure. (This assumes stock bleeder-type boost control).

Jesubi11, which line did you disconnect?

I disconected the boost control side of the "T" fitting. This was precisley what I was trying to test, boost control failure.

[knucklesplitter]

Originally Posted by Jesubi11

I disconected the boost control side of the "T" fitting. This was precisley what I was trying to test, boost control failure.

Then 'Juice is prolly right about the boost solenoid being bad. The solenoid is a normally open one, so when you disconnect it it will act the same when the solenoid is bad. Your ECU or AP will not know if the line is disconnected or the solenoid is bad - it just thinks it is cycling the valve like normal.

[Jesubi11]

What do you guys mean by boost solenoid, are we talking about the boost control. If so then why when I disconnect it from the system should the car not over boost. Also late last night I pulled the heat shield off and was able to actuate the wg arm so it is not seized in there.

[sperry]

Think of it this way:

If you have nothing connected to the wastegate, it stays shut all the time and you overboost.

If you have a simple pressure line from the turbo outlet to the wastegate, the wastegate opens based only the resistance of the spring pressure of the wastegate to the absolute boost made by the turbo, which is around 6-7psi IIRC. This is known as "wastegate boost".

If you T a boost controller solenoid into that simple pressure line, the solenoid can bleed off pressure in the line making the build up of pressure on the wastegate actuator delay opening the wastegate, thus allowing higher levels of boost than the base "wastegate boost" level.

If your boost control solenoid is out, then your car should boost like it's got a simple boost line between the pressure side of the turbo and the wastegate, with a hole in it. Which would result in slightly higher boost than "wastegate boost". Which is exactly what you're seeing. So try trading the boost solenoid and see if it fixes the issue.

[Jesubi11]

Oic... ok then i'll try and source a solenoid to test it then. So if on an otherwise properly running wrx you were to disconnect the line as I specified you would get the same results. I did not know that I just figured it was the same as disconnected entirely. Do I have this right now. I had misunderstood how our wg actuators worked. I thought that they would basically stay closed until they were told to open.
Thank you for all your help guys.

[sperry]

Originally Posted by Jesubi11

Oic... ok then i'll try and source a solenoid to test it then. So if on an otherwise properly running wrx you were to disconnect the line as I specified you would get the same results. I did not know that I just figured it was the same as disconnected entirely. Do I have this right now. I had misunderstood how our wg actuators worked. I thought that they would basically stay closed until they were told to open.
Thank you for all your help guys.

They do stay closed until they're told to open. It's the pressure from the turbo that opens them. Without a boost controller, you're limited to less boost. A boost controller lowers the pressure on the line between the turbo and the controller actuator, allowing more boost than the wastegate would otherwise.

Here's the plumbing:



Here are the actual parts:



Without the boost controller bleeding off pressure in the line, the actuator sees all the boost the turbo's making and opens too soon.

[Jesubi11]

Nice. Thank you so much for spelling that out for me. So the boost control actually introduces vacume in to the wg actuator. Now it makes sense to me why having it disconected would yeild slightly higher than wg boost.