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Thread: Fuel Tank Pressure

  1. #1

    Default Fuel Tank Pressure

    In conjunction with a new Sniper I purchased & installed the 12-304 for my 1970 Camaro. Tank is a new aftermarket "stock style" tank and I've replaced the gas cap, but the tank becomes pressurized when I'm driving. I hear the tank go "bmpfff" when I shut the engine down, it whooshes when I take the cap off, and I can hear it hissing through the cap for a few minutes after I shut the engine & fuel pressure off. Is this a problem? If so, how do I fix it?

  2. #2
    Join Date
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    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  3. #3
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    Oct 2020
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    @rustles: Seems that 1970 Camaro has two different schemes for venting the gas tank. Old-school vented cap or sealed tank to charcoal canister. If your car has been modified or the cap replaced in the past you might not have a proper vent. You could try running the car with the cap loose in place (not sealed) to confirm the lack of venting. If the symptoms are improved, your vent is absent or inadequate. Read this NastyZ28 forum post for tank venting info and pictures: gas fuel tank venting, return lines, charcoal canister
    Last edited by Candu SNO; 05-05-2021 at 07:15 AM.

  4. #4

    Default

    Quote Originally Posted by rustles View Post
    In conjunction with a new Sniper I purchased & installed the 12-304 for my 1970 Camaro. Tank is a new aftermarket "stock style" tank and I've replaced the gas cap, but the tank becomes pressurized when I'm driving. I hear the tank go "bmpfff" when I shut the engine down, it whooshes when I take the cap off, and I can hear it hissing through the cap for a few minutes after I shut the engine & fuel pressure off. Is this a problem? If so, how do I fix it?
    It's very likely that what you're hearing is not pressure build up, but vacuum is created in the tank as fuel level goes down. When you open the sealed gas cap, air rushes in. Andrew
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  5. #5
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    Dec 2009
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    Connecticut
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    Yes, that's exactly what's happening, especially after long drive. The fuel tank simply must be vented, see post #2 above.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

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