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Boost leak through secondary air pump? 06 WRX 2.5

5048 Views 2 Replies 1 Participant Last post by  NCW
Exhaust leak through secondary air pump? Valve open, no code? 06 WRX 2.5

First post! Thank you all in advance for your advice and help.

---Info about the car---
The car in question is a mostly stock 2006 WRX Wagon. The only mods that are really notable to the engine are a catback exhaust, and Mishimoto turbo inlet. I purchased the car September 2016, and it has ran pretty well other than the fact that it seems to only have wastegate boost pressure (about 7psi max). I only knew that there might be an issue since I installed my boost gauge last month.
I checked all the common stuff: BCS is clean, clicks when power is added, even swapped for a known good one. The line from the compressor has the proper restrictor pill, and hoses are in good shape. Wastegate actuator operates normally. I have an Autometer Tee'd off the BPV line and it reads generally about 20-21 vacuum at idle.
I had borrowed an accessport from my brother, to do some data logging. Car hits 7psi boost in all gears up to redline, DAM is 1.0, no knocking, Wastegate duty cycle hangs around 28-32% at WOT. No roughness counts on any cylinders.

The car has all new OEM gaskets on the engine, I have the paperwork showing it has had proper maintenence following the book. Timing belt, idlers, water pump replaced at 100k miles.

I tightened all the hoses and vacuum lines that I can get to, I don't hear any vacuum leaks.

The car throws no CEL's except occasionally (maybe once a week at most) a 'P0442 Evap Emission Control Small Leak Detected'.

---Here is what I found---

The other day I took a 20 minute drive around and decided to pop the hood while the engine was running. I saw a wisp of smoke/vapor coming from the edges of the secondary air pump. There seemed to be moisture seeping from the edges of its plastic 'turbine' housing.

I pulled the large hose off the output of the pump, and I could hear and feel pulsing exhaust coming out of it. I had my brother slowly rev the engine up to about 4000rpm and with my finger over the hose I could feel boost pressure blowing out, along with some vapor/smoke. If I plug the hole with my thumb completely, and have the car revved up to 3-5k, I can feel considerable pressure pushing out. The below photo shows what I am talking about. Is this normal operation?

My question is, without and CEL codes (unless the P0442 pertains to this, or is it possible that the codes were eliminated before I bought it?) is my air injector valve(s) stuck open allowing exhaust to blow up into the secondary air pump? Would this explain why my boost is limited to 7-8psi?

Again, thank you all for any help you can give me. I appreciate it!


[Hose removed from pump to show exhaust vapor leaking out (it was 20ºF out) and the car had been warmed up to temp and driven for about 15 minutes]

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I ordered some blocking plates, the type that get installed between the valve and the exhaust pipe going to the block. I figure at least that will stop the exhaust from backing up into the air pump. Hoping that will solve the low boost issue I've been chasing for a month!
I was able to get the job done. It was not as easy as one would think but it is doable in an afternoon.

My valves were so badly rusted and corroded inside, they just passed air straight through- despite them being "closed". Even the check valve flapper was not seating properly. Capping them off was definitely necessary.

It didn't completely solve my low-boost issue, but I think it helped. Before I was only able to reach about 7psi, now I can hit 9 at about 4500rpm in 3rd. Going to keep working at it and figure it out.
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