I need to vent...Outback slow filling

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  • Trindaddy
    Senior Member
    • Jan 2010
    • 339

    I need to vent...Outback slow filling

    Hi gang. Got a story for ya. This 99 Outback (AWD) will only take fuel very slowly. So, to pinpoint the problem I've done a few things and raised some questions. 1st i checked the drain/vent valve and bypass valves. The drain works well and the bypass quietly clicks but i couldn't test its flow as it is in a bad spot and the lines are rusty. Anyhow, the one good source i had indicates that few things are involved with venting during fueling. Regardless, i began opening all the lines in hopes of finding a blockage while using the EELD to push air into the filler neck. No matter what i did, no flow. As the leads narrowed i had to get access to the tank vent valve. It is located at the top of this rusty tank and requires removal of tank to access. Now as you may know, this is not an easy task on these Subarus. On this one, its not worth doing. This ol girl is very rusty (like most 12yr old cars in New Hampshire) is will not be coming out without consequences. So, i made my own access panel in the cargo floor. After gaining access i found the vent line is not blocked and i removed the vent. With vent in hand, i taped the side holes shut and blew into the one remaining opening to find it works. However, their is a smaller line at its top with a diaphragm that effects operation. It goes into the tank cavity and also to the top of the filler tube above the 2 hose valve that closes when filling. Here is the question (i know, you thought I'd never ask!), when any vac, pos. pressure, or block is applied to this port the vent wont open. How then does it work? It appears that this small port is going to "see" the same pressure build as the tank when filling. Does anyone have some good test for this? There is some apparatus in the tank that also has me concerned and i cant reach it. I ordered a new valve out of desperation and the car is scheduled to return in 4 days. I am not sure how this valve is supposed to work after my interrogation and how other parts could impact my "diagnosis". Could use some advise. Thanks again.

    Neil
  • SnapOnKid
    Senior Member
    • Jan 2011
    • 870

    #2
    I am supprised some one else has not run into this...

    Since you mentioned the heavy rust, I wonder if there is debry blocking the flow/ function of that valve you mentioned... Sounds like maybe a Bypas valve or something. Un-fortunintly I have no evap experince with that brand.

    I Hope some of our resident Guru's can help you out as they have me today.

    Comment

    • SnapOnKid
      Senior Member
      • Jan 2011
      • 870

      #3
      No buddy has any advice on this one???

      Comment

      • Trindaddy
        Senior Member
        • Jan 2010
        • 339

        #4
        Hey thanks "SO kid", i'm no worse off than when i started anyway. Tomorrow i'll have the car again. I think i'll come to work with no shirt that way i can't lose it again! I'll post results soon.

        Neil

        Comment

        • SnapOnKid
          Senior Member
          • Jan 2011
          • 870

          #5
          Originally posted by Trindaddy
          Hey thanks "SO kid", i'm no worse off than when i started anyway. Tomorrow i'll have the car again. I think i'll come to work with no shirt that way i can't lose it again! I'll post results soon.

          Neil
          I read up on these piles on a forum at lunch and a dealer said they sale a lot of the filler neck assembles with a valve that is attached to it Or some how goes to it. I'm guessing there must be a bypass valve or vent. Have not had time to look it up yet myself. Thought I would try and give you an idea on things to look over... Keep us posted on what you find.

          Comment

          • Dan Cam
            EBI Application Specialist
            • Dec 2006
            • 43

            #6
            Had one in the shop last Month same issue also from back east we found that the filler tube & the SHUT valve (at the top of the filler neck) had become block from the rust in the filler neck if your going to replace the SHUT Valve you should replace filler neck. The Shut Valve is suppost to shut when filling the Tank if stuck open causing pressure to build up in the tank not letting you fill the tank I got this info from a Master Tech Subaru technition Hope this helps any questions let me Know Dan

            Comment

            • SnapOnKid
              Senior Member
              • Jan 2011
              • 870

              #7
              Originally posted by Dan Cam
              Had one in the shop last Month same issue also from back east we found that the filler tube & the SHUT valve (at the top of the filler neck) had become block from the rust in the filler neck if your going to replace the SHUT Valve you should replace filler neck. The Shut Valve is suppost to shut when filling the Tank if stuck open causing pressure to build up in the tank not letting you fill the tank I got this info from a Master Tech Subaru technition Hope this helps any questions let me Know Dan
              Thanks for the reply Dan!

              Thats sort of what I have found on the net and pieced together from various descriptions. Glad some one could confirm it with an actual Fix. Even found this picture of the new parts in one of the links I read...

              Comment

              • Trindaddy
                Senior Member
                • Jan 2010
                • 339

                #8
                Hello again kind contributors and staff! It was smokin hot around here today, one of the hottest days i can remember. Good day to lose your shirt . Here's what i learned:
                The tank vent (at top of tank) is only allowed to remain open if atmospheric pressure is "seen" at the diaphragm above it. I believe this line is called the differential pressure sensing line, and is open inside the tank and also goes to the top of the filler neck above the mentioned shut valve. The venting of air during filling is actually much simpler than the rest of this system. I goofed this up starting the other day with my initial diagnosis. I figured to simulate the entrance of fuel and therefor the release of air from the tank cavity i would use the EELD tester to push air into the tank via the filler tube. When i did this, the tank air wouldn't vent despite all the lines being open. What was actually happening was the psi introduced into the tank at the neck was essentially blocking the sensing line at both the tank cavity and the neck. When ANYTHING but atmos. is on this line the tank will not vent. So actually, today i realized i really didn't have a problem. The air from the tester would not vent FROM THE TANK using my method. By simply unplugging the line at the tank vent top or at the filler tube end it vented fine. After i realized this i removed the fuel from the tank with my caddy then filled it again as fast as i could. It filled normally. Then i went to the station and filled it with 5 gals more at full speed, normally. Flow testing this system may be handy to check for leaks and verifying canister vent operation, but i feel it does nothing to verify the tank's ability to vent air during filling. In the end, i believe that the customer's slow filling event was most likely caused by an intermittently sticking canister vent as is often the case with these cars. we replace many around here as they are in a poor spot to survive the snow, salt and dirt roads. Usually though we see a code that suggests this drain valve is the issue. This time i had a code P0453- High pressure input. I hope i don't see this again because i don't have a way to figure this using the Modis and the chart for it. Turns out the chart requires the use of the tank psi pid IN INCHES OF MERCURY and the Modis doesn't have this PID at all, nor do i have a chart that shows the psi/voltage relationship. For example, i measured 2.5v at the signal wire at the pcm from the tank press sensor but the chart only refers to measurements in inches of mercury. Unfortunately I don't see a way for me to properly prove out this code using the Modis. No where in this lengthy chart is the tank vent or the canister vent indicated as the problem! Go figure. Perhaps i have 2 problems here. I gave away my time today as i felt there was too much i didn't understand to be proficient. I did learn a lot on this one but i still don't have a very clear picture of what the possibilities for one result or another is with this system and my scenario. Again i found this site and you guys make a tough job more rewarding and fun. Thanks for the help again guys.

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