Hi all,

I am in the process of cleaning the boost control solenoid and would like to understand fully how this system operates as this is my first turbo car (owned many NA cars previously)

Clearly the solenoid is the gold part pictured below, but what is the black part above it? It was sat on top of the solenoid...



Then secondly, what on earth is this part here:



It is connected to the bottom of the the part pictured below, and the other side is routed to the airbox (well, to a samco hose, non standard) I would take a guess that it is a restrictor, but I am unable to remove it from the car to inspect it (tight pipe!) because if it isnt... I can't find it!



So what is the part pictured above, along with the rest of them?

Thanks,

 

top pic is a map sensor, middle is a one way valve if you blow in it you can check to see if its working. bottom pressure exchange valve.
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Whats the function of the pressure exchange valve? So I guess I dont have a restrictor pill... as far as I can tell. If I add one but there is in fact already one there, will this be a problem, or should I make certain there is not already one there?

Thanks,

 

It'll be easier to understand what it does when you realise that Subaru refer to the "MAP sensor" as a "pressure sensor". The function of the pressure source change solenoid is to switch the pressure sensor from reading manifold absolute pressure (which it does most of the time) or atmospheric pressure (which it updates every few minutes). Atmospheric pressure is read through that little black barrel filter sticking out the side of the change solenoid. MAP reads through the pipe running to the inlet manifold.

The ECU needs to know what the atmos pressure is as, among other things, boost pressure is calculated relative to the atmosphere.

Incidentally, Oadamo isn't quite correct re. the function of the white object with (the remains of) foam around it. It's a filter, not a one-way valve.

If you can't feel one in the pipework, you don't have one. Given the pictures you've posted you have a three port solenoid, and thus presumably either have an STi version 4. I don't recall whether these are supposed to have a restrictor, but if they do, you're most likely to find it in the pipe that runs from the solenoid back into the inlet tract.

What's the context of the question? Are you just asking because you'd like to know, or are you trying to diagnose some sort of boost control problem.

 

I appear to be over boosting, so was just going to check everything boost control related. I don't know whether the car (sti ver 4) has been remapped and toyed with to allow higher boost, but its hitting 1.2 bar. gears 1-3 seem to be about 1.1 then 4 and 5 seem to be about 1.2. This is using the peak function of my boost gauge. It is a digital gauge, so i'm not certain of its accuracy, therefore the ECU might think the boost is in fact lower than what I imagine it is.

So you think I might not actually need the pill? Good to know, I guess. I couldn't feel one when I had a quick check earlier, but I would have to look again to confirm.

Thanks for the replies,

 

1.1 bar is normal. 1.2 & 1.3 obviously means your over boosting. However some gauges are not the best in reading the boost correctly as the needle goes over slightly. I had a universal boost gauge in one of my Impreza's along with an Apexi AVCR & the AVCR was giving me the correct reading whereas the Pivot boost gauge was giving me 5psi more. I tried my mates Defi gauge just to make sure & the reading was perfect. Just a dodgy gauge!