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Old 03-27-2013, 08:34 PM   #1
IA Performance
Former Vendor
Member#: 25194
Join Date: Sep 2002
Chapter/Region: RMIC
Location: Boulder, CO
2008 Forester XT 5mt
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Default FAQ: Subaru EVAP Purge Control Solenoid Valve Information for EJ205

After receiving quite a few questions regarding the EVAP Purge Solenoid hose routing we figured it best to start a FAQ thread dedicated to the ej205 (WRX 2.0L).

Note: We are learning more about the system along the way so please bear with us as we aren't experts in this field.

General EVAP FAQs
What is EVAP
Evaporative Emission Control System

What is the function of an EVAP System?
I tried to make this as short as possible: The EVAP system was designed to decrease fuel vapors as a source of pollutant. You see, gasoline vapors contain hydrocarbons. These hydrocarbons mix with air and sunlight to create smog, a pollutant. To curtail the smog output the car's gas tank vent's the fuel vapors, via the vent tube, to the charcoal canister, which serves as a temporary holding tank. So what's inside of a charcoal canister? You guessed it, charcoal. This activated charcoal absorbs the vapors and holds them until the car is fully warmed and driving. At this point, the ECU sends a few signals out. One, to the charcoal purge alerting it to open, as well as one to the EVAP purge solenoid, alerting it to open under vacuum. The vapors are then drawn from the charcoal canister, by vacuum, into the intake manifold, where they are ultimately burned up.

For a more in depth description we suggest doing a internet search. There are several good sources out there. *

Subaru WRX ej205 2002-2005 Specific FAQs
Is the EVAP Solenoid Open or Closed when at rest (no power)?

Is there a specific flow direction for the EVAP purge solenoid?
Through research, it appears the direction does not matter since the solenoid is simply creating an open or closed path for which the vapors to flow. When open, air can pass either way through the solenoid. Although, we still recommend following the factory Subaru diagrams for your specific model.

Is there a specific flow direction for the purge valve?
The Purge Valve (round black thing) is direction specific and should have an arrow painted on the front of it. Please take note to diagram A for direction.

Which hose goes where?
Please see the diagram below for 2002-2005 ej205 applications. Note, if you have a 2.5L turbo motor please refer to our EVAP purge FAQ for ej25 turbo models here.

It looks like spaghetti, can I decrease the EVAP clutter?
Yes, you can install the purge control solenoid without the use of the Purge Valve (black round item with 3 ports on it). A perfect example of a EVAP system that does not require the Purge Valve is the JDM Subaru ej207. This model still uses the same EVAP purge solenoid, but the mess of hoses is cleaned up considerably (only 2 hoses now). A WRX ej205 can be setup in the identical fashion. There does not appear to be an affect on performance, nor does it trigger a CEL. In short, all it takes to run the EVAP purge solenoid is the valve, 2 hoses, and 2 hose caps to block off the unused nipples. Disclaimer: We do not know how this affects pollutant levels.

Do I need to be concerned with leaks (vacuum as well as pressure)?
Yes, a pressure, as well as vacuum, leak can have a great affect on the way the car performs. A vacuum leak will allow non metered air into the intake manifold, which creates a lean condition when the intake tract is in vacuum. As the car builds positive pressure (PSI) it will then allow air form the intake tract to escape through this leak. Since the ECU is unaware of this leak it continues to add the same amount of fuel, which leads to a rich condition during positive manifold pressure conditions (full throttle is especially affected).

We suggest using zip ties at any hose connection on the intake manifold, EVAP system, as well as turbo inlet tube. P.S. don't forget to do the same for the Fuel Pressure Regulator hose

Below are the most common EVAP related leaks that we've run across that will affect the performance of the ej205:
1) The junction of hoses at the blue 'T' connector, located behind the P/S pump. As the hoses dry out they become lose and come apart.

2) The next most common leak area is the ~1" long, straight, hose going from the intake manifold to the Purge Valve. Since there are no hose barbs at either end of this hose it can easily come off the manifold and/or Purge Valve. As a rule of thumb, any hose nipple should have a barbed end on a boosted motor. If this hose is lose we suggest replacing it with a new one. Just about any vacuum line will do, assuming it has the same ID.

3) One of the more expensive leaks is created when one of the EVAP Purge Solenoid nipples is broken off. This seems to happen the most when people [cough] carelessly install an aftermarket turbo inlet tube. If this happens do NOT glue it back together. Rather, spend the $100+ and replace the unit with a new one from Subaru. There are way too many negative side affects with a broken valve (pollution, loss of power, etc).

*rabech27 contributed the following on 9/18/2014:
The charcoal you refer to is actually activated carbon pellets. I worked at the only plant in the world that can make the grade of carbon that goes into those canisters. Mead Westvaco is the company that makes it and their plant is located in Covington, Virginia. I worked there as an engineer for three years. It is made with sawdust and phosphoric acid, heated in a large rotary kiln (100 ft long), then shaped into pellets, and run through another kiln that activates it and creates the adsorption characteristics that hold the fuel vapors. The activated carbon has millions of pores that hold the fuel vapor molecules until the purge system opens and purges the vapors off the carbon. Just thought I'd share that with you in case you were interested.

Last edited by IA Performance; 09-22-2014 at 01:30 PM.
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