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Thread: NA gas fume problem SOLVED

  1. #1
    Forum Sponsor revlimiter's Avatar
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    NA gas fume problem SOLVED

    I just did a blog post about fuel fumes. I'd done one back in 2012 which helped, but I was never able to figure out exactly what was causing them to return until now.

    I did three things:

    -Removed the little white check valve after the rollover valve
    -Added header wrap to my exhaust under the fuel tank
    -Put in a new evap canister and retired the old one.

    Read about everything here. But I feel that the magic bullet was the check valve. I'll paste all of that below.



    After my trip to Grand Canyon and Bryce with my daughter, I went on a mission tearing things apart in Sharka to fix the gas fume problem. In the heat of the summer and with the huge elevation changes, the fumes were really really bad. Happily, not so bad when driving but if we stopped for even a minute, they would start to creep into the cabin.

    So I started investigating once we were home and Sharka could be on jack stands for a few weeks. I started by popping a hose off the charcoal canister (evap expansion tank) and pressurizing the fuel tank manually with some compressed shop air. Not a whole lot of pressure, just a few puffs from the air gun so that I could hear the tank expand. Then I held the hose to my hand (or cheek, lol) to feel the pressure escape.

    Nothing. No pressure ever escaped.

    Suspecting I had a lot of crud built up in the hardline between the evap tank and the fuel tank, I opened up both ends of that hardline (the other is right near the tank) and powered a huge amount of pressure through it with my air compressor in both directions.

    This hard line cleaning didn’t do much for me and almost nothing was jammed in that line. A few specks of dirt came out of either end, but air flowed freely through the line all the time.

    The only other things between the tank and the charcoal canister are the rollover valve and that little white check valve. As it was the easiest next step, I swapped a piece of straight hose in place of the check valve hose and reconnected the hard line.

    I pressurized the tank as before. The tank expanded audibly. Then I released the air gun and… THE TANK RELEASED PRESSURE.

    So the failure mode of that little valve – WHICH IS SUPPOSED TO RELEASE PRESSURE – is to not ever release anything and become blocked. Cleaning it lasts for a few months to a year and then it is back to its previous dangerous behavior.

    I deleted the valve permanently and used a piece of silicone hose instead. And I did this months ago – back in August 2018. I’ve been sitting on this post since then, driving around and making sure the pressure didn’t return.

    The fuel tank fumes and overpressure condition never returned.

    CAUTION! This may not be a good solution. I’d suggest sourcing a new valve from Mazda and replacing the old one.

    I hope this helps some folks out. Summer will be here before you know it. Replace that ancient stuck white valve with something better.

  2. The Following 9 Users Say Thank You to revlimiter For This Useful Post:

    Agent☣Orange (02-17-2019),Greasemonkey2000 (02-17-2019),HarryB (02-18-2019),MiataQuest (02-17-2019),Phatmiata (02-17-2019),Roadster7 (02-17-2019),RotorNutFD3S (02-26-2019),speedypenguin (02-19-2019),vote4pedro (02-17-2019)

  3. #2
    4,000 rpm - entering the fun zone Roadster7's Avatar
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    This has been on my to-do list for ages. Thanks for the write-up Adam, will be doing this in a few days.

  4. #3
    Forum Sponsor revlimiter's Avatar
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    I probably should have sat on this another 6 months just to make totally sure of my solution, but... folks have their cars torn apart during the cold weather right now. I wanted to post it.

  5. The Following 4 Users Say Thank You to revlimiter For This Useful Post:

    Agent☣Orange (02-17-2019),Greasemonkey2000 (02-17-2019),Roadster7 (02-18-2019),RotorNutFD3S (02-26-2019)

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