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Thread: EVAP and tank pressure issues - where to start

  1. #1
    Huh? What?

    '03 p5 and '89 4Runner; M5 (wife's)

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    EVAP and tank pressure issues - where to start

    Awhile ago my P5 started throwing a P0455 code, EVAP leak etc. If I clear it, comes back in around 50 miles or so.
    Since there are tons of things that can cause this and there was no sign of performance change... I did what any red-blooded American would - ignored it

    Just this week I went to fill it up, and the gas pump clicked off after 0.5 gal. No matter what I tried, it kept auto-shutting off after tiny amounts of gas.
    I tried another pump, same thing. Been to 2 other stations, same, so yes, it's the car.

    I'm assuming that something is causing a vent problem that's bad enough that pressure is building in the tank and can't escape when filling up.
    Any tips on the most common place to start?
    If it matters - for the longest time, I've had a slow accumulation of black specs (like soot) around the gas cap door. The inside looks like a chimney, it would slowly accumulate on the body just above the door. I assumed this was some mild venting issue, but again, figured it'd be a PITA to pin down so just ignored it.
    However - that dosn't seem to be happening now.

    So to me thats more proof of a clogged vent somewhere... but where to start?

    Thanks
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  2. #2
    Old and slow, unlike my 5 KBrian's Avatar
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    Registered Member P-Funk!'s Avatar

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    As soon as you open the gas cap - you vent the system.

    Does it make a big pssssh?

    The evap leak could be the gas cap - replace it.
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    '03 p5 and '89 4Runner; M5 (wife's)

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    Quote Originally Posted by P-Funk! View Post
    As soon as you open the gas cap - you vent the system.

    Does it make a big pssssh?

    The evap leak could be the gas cap - replace it.
    No, no woosh.
    And that wouldn't explain why every gas nozzle auto-shuts off quickly.
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  5. #5
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    Protege5

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    I had that damn P0455. There's a pinhole, somewhere....

    A smoke tester is really the fastest way to do it. There is an article or forum post somewhere that shows how to make one with a fog machine.

    There is also apparently a spider that is attracted to gas fumes, and likes to make nests in the vent hose. I'm not shitting you either, pcb knows more about it.
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  6. #6
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by MrGiggles View Post
    ... There is also apparently a spider that is attracted to gas fumes, and likes to make nests in the vent hose. I'm not shitting you either, pcb knows more about it.
    I found this...



    Quote Originally Posted by RatLabGuy View Post

    So to me thats more proof of a clogged vent somewhere... but where to start?

    Thanks
    Start with what's easiest... The non return valve is inside the gas tank and the fuel shutoff valve is hard to get to as well... They require removing the gas tank.



    If it were me, I'd disconnect the rubber hoses and try to stuff something like a bicycle brake cable though the piping to find any blockage.
    Check the "air filter" and catch can to see if they are full of gas.




    Last edited by pcb; 12-21-2015 at 09:07 AM.
    The Diagram Dude

  7. #7
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by P-Funk! View Post
    As soon as you open the gas cap - you vent the system.

    Does it make a big pssssh?

    The evap leak could be the gas cap - replace it.
    I don't think that's right... My car has never made a whoosh when I open the gas cap...

    But... +2 on replacing the gas cap...

    The fuel and emission sections of the FSM are kinda hard to follow.... I assume the air being pushed out when filling the gas tank flows through the catch can and air filter to the nozzle??... So any blockage or liquid gas will "trip" the nozzle.

    More pictures to puzzle over....








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  8. #8
    The Diagram Dude pcb's Avatar

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    This might come in handy...





    And remember BE CAREFUL.. you may encounter drug crazed arachnids !!!


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  9. #9
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    '03 p5 and '89 4Runner; M5 (wife's)

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    Thanks.
    So now that it's not rediculously cold I finally started back at this...

    First, it's not a gas cap issue - b/c it happens when I'm filling up w/ gas. Clearly something has caused a blockage of air to get out during the filling process. Now, yes, there may also be something else causing the CEL but I'll deal with that if it persists after the fill issue.

    I dug around under the rear of the car, no obvious bug infestations. Plenty of rust though ;-).
    I disconnected the lines going in and out of the charcoal canister there, and bypassed it - blowing through it was hard so I tink it may be filled w/ moist fluid like it got gas in it.
    So now the lines go from the CDCV right to the air check valve.

    I was all excited when I started pumping gas, and it didn't click off... until I noticed some dripping out of the check valve. Doh!

    I've since added gas a couple of times, and it has dribbled some gas out of the check valve behind the CDCV each time. Not gushing like I'm losing gallons, but enough that the EPA would not be happy...
    What this tells me is that something else is clogged and gas is getting pushed through this whole end of the system b/c it has nowhere else to go.
    So - looking at the diagram on P 7 here - http://www.mazdaspd.com/manual_files/01-16.pdf
    just to be clear, there should not be gas going to anywhere right? Only vapors?
    Next I suppose I'll try checking everything going in and out of the charcoal canister. My assumption is that if I disconnect the line coming out of that which goes towards the font of the car, I should be able to blow from there up the line to the catch tank and purge vale... right?
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  10. #10
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by RatLabGuy View Post
    My assumption is that if I disconnect the line coming out of that which goes towards the font of the car, I should be able to blow from there up the line to the catch tank and purge vale... right?
    The FSM is hard to follow... There's no flowchart ???

    My assumption is that you should find no liquid in any evap system ?? ( that and spiders of course...)
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  11. #11
    Huh? What?

    '03 p5 and '89 4Runner; M5 (wife's)

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    Well I took the small line off of the charcoal canister, and blew through it - nothing.
    Then I realized the purge valve may be closed. Disconnected it at the purge valve - then I could just *barely* blow through it. So I used my compressor to try and open it up a little bit, first at the catch can, then from the can to the purge valve. No resistance between the can and valve, but best I could get was still a bit of resistance between the canister in the back and the catch can. Better than it was before though.

    After going through all that, and connecting it back up, it occurred to be though that if the normal state of the purge valve is to be closed when the vehicle is off, then than whole line is blocked while filling gas anyway. so it shouldn't be used as a vent line. I'm sure cleaning it out was good for it - but now I have it narrowed down (I think) to teh charcoalcanister itself. Will pop it off later tonight and inspect.
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  12. #12
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    '03 p5 and '89 4Runner; M5 (wife's)

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    Quote Originally Posted by pcb View Post
    The FSM is hard to follow... There's no flowchart ???
    actually page 1-16-6 is pretty helpful. It dosn't show direction of flow but you can figure it out.
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  13. #13
    The Diagram Dude pcb's Avatar

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    I've stared at that a few times... It doesn't really tell what to look for... There's valves and things involved... You don't know whether or not they're supposed to be open or closed and at what pressure ???

    There a whole bunch of tubing it doesn't show...

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    Ive taken mine apart twice now. I had gas pooled in the canister the 1st time. It helped one gas fill up. I tried just now to clean everything and had liquid in the canister and the cdcv. The check valve had nothing in it. I had air flow through all of these in both directions. Should the cdcv be closed off in one direction? The spring inside moves freely.

    I put about 4 gallons in it just now and had no issues where I could only do about .2 of a gallon before shut off.
    I hope it doesn't come back

  15. #15
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    protege5

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    When mine was doing that I found a check valve on the vent line under the car was caked in mud because I live on a dirt road, and it was unable to "vent" because it had so much mud on it. I blew it out/off real well with compressed air and have had no issues since then

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