uniberp Posted March 24, 2008 Share Posted March 24, 2008 Does this thing stick open when it fails? http://www.subarupartsforyou.com/cp_partdetail.php?partid=6374 I want to just buy it and swap it, but that would be not be diligent on my part. Is it a common failure part? 155k miles. I disconnected it, and the very rich stink at idle disappeared on the next startup. If it stuck open or opened on start that would make sense, sincve vacuum is highest at idle, and any available source will be sucked in. Does it activate by default when the engine is first started? Does vapor build up and trigger it through some other pressure sensor? I suppose I could run some solvent through it to see if it clears up. I understand that vapor can build up and exhaust to atmosphere if it is not connected. Sorry about the eariler thread aboutthe CoolanTempsensor, but that may come in handy after this is solved. mpergielelmhurstil97legato"sport"99forester. Quote Link to comment Share on other sites More sharing options...
aircraft engineer Posted March 24, 2008 Share Posted March 24, 2008 I can't tell you how it fails, but I can tell you what it does - It's there to pull air thru the charcoal canister that collects the gas vapors off the tank. The "purge" means that it allows the "excess" collected vapors to cycle into the engine intake manifold and be burnt in combustion. If you are smelling a "rich" mixture right at startup, that's actually normal because the purge doesn't start until the engine is warmed up and the gas isn't well "gasified" from the injectors so the engine runs "rich" (and smells like "raw gas" sort of) I SUSPECT (don't know for sure) that it would fail closed unless there is a restriction in the solenoid to hold it "open". Most of those are spring loaded to close because of "roll over" issues in fuel system integrity. You might want to check the hoses first and see if there are cracks Quote Link to comment Share on other sites More sharing options...
EVOthis Posted March 24, 2008 Share Posted March 24, 2008 i always wondered what the pressure exchange solenoid did.......thanks for the info aircraftengineer...... Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted March 25, 2008 Share Posted March 25, 2008 i always wondered what the pressure exchange solenoid did.......thanks for the info aircraftengineer...... Actually what he described is for the canister purge solenoid. The pressure exchange solenoid is used to switch between taking readings from the atmosphere, and intake manifold vacuum readings. This is done to compensate for barometric pressure changes due to weather and elevation. Quote Link to comment Share on other sites More sharing options...
EVOthis Posted March 25, 2008 Share Posted March 25, 2008 i took a look at some pics and they seemed the same....look the exact same and mounted in same location......thanks legacy777.... Quote Link to comment Share on other sites More sharing options...
uniberp Posted March 26, 2008 Author Share Posted March 26, 2008 I can't tell you how it fails, but I can tell you what it does - It's there to pull air thru the charcoal canister that collects the gas vapors off the tank. The "purge" means that it allows the "excess" collected vapors to cycle into the engine intake manifold and be burnt in combustion. If you are smelling a "rich" mixture right at startup, that's actually normal because the purge doesn't start until the engine is warmed up and the gas isn't well "gasified" from the injectors so the engine runs "rich" (and smells like "raw gas" sort of) I SUSPECT (don't know for sure) that it would fail closed unless there is a restriction in the solenoid to hold it "open". Most of those are spring loaded to close because of "roll over" issues in fuel system integrity. You might want to check the hoses first and see if there are cracks I'm replacing the part because it makes a consistent night-and-day difference in the rich smell and drivability when it was disconnected and reconnected several times. What I suspect is that it is opened at startup to purge and possibly provide a little richness as a side benefit. This one is aged and sticks open and wrecks cold drivability. Positive gas vapor pressure may be produced when the car is simply sitting, just like a gas can will pressurize if left outside. Quote Link to comment Share on other sites More sharing options...
uniberp Posted March 26, 2008 Author Share Posted March 26, 2008 Actually what he described is for the canister purge solenoid. The pressure exchange solenoid is used to switch between taking readings from the atmosphere, and intake manifold vacuum readings. This is done to compensate for barometric pressure changes due to weather and elevation. Is that what they call the "bypass valve" in the Haynes diagram? Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted March 27, 2008 Share Posted March 27, 2008 Is that what they call the "bypass valve" in the Haynes diagram? Probably not. What context was Haynes using the term bypass valve? Quote Link to comment Share on other sites More sharing options...
uniberp Posted April 2, 2008 Author Share Posted April 2, 2008 Probably not. What context was Haynes using the term bypass valve? (From memory) Look at the diagram of the fuel injection system for N/A engines. There is a 'control bypass valve' in the upper middle somewhere. From what I can see underhood ( and the diagram), it simply shunts air bypassing the throttle plate for some reason, from near the air filter to the intake near the head. It could be an auxiliary air valve for cold start. How would it explain the increased performance and gas mileage is disconnected. The valve tests OK. I'm sure it's responding to some other input, but what? Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted April 3, 2008 Share Posted April 3, 2008 The air bypass valve is again something different. It's also known as the idle air control valve. Here's a picture of the IAC valve http://www.main.experiencetherave.com/subaru/images/injectors/DCP_2470.JPG Picture of the canister purge solenoid valve http://www.main.experiencetherave.com/subaru/images/injectors/DCP_2471.JPG The pressure exchange solenoid can be seen near the top left of the picture. It has the brown connector facing up http://www.main.experiencetherave.com/subaru/images/ej22t/32/DCP_6012.JPG Quote Link to comment Share on other sites More sharing options...
mwbean Posted November 8, 2011 Share Posted November 8, 2011 Thanks to Legacy777 for the PIC of the Vapor Canister Purge Valve I have a 1992 Legacy Outback Wagon and it appears to be under the intake manifold on the R/H (passenger side) it has a blue connector. the haynes book says to chek the valve, measure the resistence it should be between 10 and 100 ohms. does sound about right?? Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 8, 2011 Share Posted November 8, 2011 No - it should be about 35 ohms. The book is pretty vague. GD Quote Link to comment Share on other sites More sharing options...
mwbean Posted November 8, 2011 Share Posted November 8, 2011 Thanks to Legacy777 for the PIC of the Vapor Canister Purge Valve I have a 1992 Legacy Outback Wagon and it appears to be under the intake manifold on the R/H (passenger side) it has a blue connector. the haynes book says to chek the valve, measure the resistence it should be between 10 and 100 ohms. does sound about right?? Thanks GD I Checked it with a VOM and it has a open. Guess I will have to buy a new one ugh Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 8, 2011 Share Posted November 8, 2011 Thanks GD I Checked it with a VOM and it has a open. Guess I will haveto buy a new one ugh You don't *have* to buy a new one. Replace it with a 35 Ohm, 5 watt resistor for about $1 and the ECU will quit complaining. The job of that solenoid is to open the port that pull fuel vapor from the charcoal canistor. You won't miss it if you just just plug the lines and fool the ECU. GD Quote Link to comment Share on other sites More sharing options...
LeolaPA Posted January 31, 2012 Share Posted January 31, 2012 Does this solenoid have anything to do with the MAP sensor and it's pressure solenoid? If I have incorrect voltage at the map sensor could this solenoid cause that? Quote Link to comment Share on other sites More sharing options...
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