504 gas fumes in trunk
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  1. #1
    Fellow Frogger!
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    Default 504 gas fumes in trunk

    When I open the trunk to my '74 504 GL (running or not) I smell gas pretty strongly. The rubber filler hose to the tank looks OK to me and all the other connections look intact as well although honestly I havent quite figured out the plumbing back there. Any thoughts as to why I have this pronounced gas smell or is this just normal?

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  2. #2
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    I sggest lifting up the rubber bung which hides the fuel gauage and checking to see that everthing is tight, and that the seal is still intact. It's also possible that the rubber fuel line between the tank and the pipe has perished. It did on my 504, and I haven't had a problem since.

    Also if your car has the return line which comes into the fill neck, it might be broken at that point, though I think this may be only an off chance.
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  3. #3
    Fellow Frogger! Tom_95's Avatar
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    It would be worth checking the hoses to the "evaporative fuel emission box" in the top corner of the boot near the light. The box itself may be cracked?

  4. #4
    Fellow Frogger! Bruce Llewellyn's Avatar
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    Default Venting,

    Quote Originally Posted by Tom_95 View Post
    It would be worth checking the hoses to the "evaporative fuel emission box" in the top corner of the boot near the light. The box itself may be cracked?
    The 74 should not have an evaporative emmission system from memory. Early 504s had the same fuel cap as a 404. Then there was a non vented version of it, marked with a red sticker (it doesn't have a pinhole vent on the underside) Last (79 -80) had a cap similar to Japanese cars.

    Putting a late type non vented cap on an early car can cause petrol fumes in the boot, as the vapour gets out either past the rubber filler neck or around the gauge sender when the gasket goes hard. Also produces fuel starvation problems if you drive fast for long periods. The givaway was the bottom of the fuel tank sucked up.

    Unleaded fuels have more volitiles than leaded fuels to get the octane rating up, so putting a non-vented cap on an early 504 or a 404 probably produces more smells and less fuel starvation.

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  5. #5
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    Hmm, very interesting. My '74 504 definitely has an evap system and it also has a fuel cap with a red square sticker on it, original i assume. Coincidentally just this weekend i took a fuel cap off a '69 404 and the 404 cap as you stated has the same shape as the one on my 504 but has a pin hole on the metal part that is ringed by the rubber gasket, would never have noticed it if you had not brought it up. But as for my problem, the smell seems to be coming from the fill tube area despite the fact that the rubber filler hose is definitely clamped to the metal pipe that comes up from the tank. The rubber stopper that fills the hole on the trunk floor dosent fit snugly to pipe that comes up from the tank, not sure if this matters. Looks like I'll have to take this all apart, will report back.

  6. #6
    1000+ Posts Beano's Avatar
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    Quote Originally Posted by rpieper View Post
    The rubber stopper that fills the hole on the trunk floor dosent fit snugly to pipe that comes up from the tank, not sure if this matters. Looks like I'll have to take this all apart, will report back.
    In Australia they are plastic. No, it doesn't matter. The fuel gauge sender underneath that should be sealing the top of the tank.
    Every other connection needs to be perfect.
    I had fuel vapour coming into the boot from where the filler neck joined the body, just behind the petrol cap.

  7. #7
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    Does your car have the rubber " funnel" overflow? Check that the pipe is runing outside the car.

  8. #8
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    Had a chance to take a closer look at everything this weekend which reminded again why I love my 504, nothing could be easier to work on. Anyway, took apart the entire filler neck system - cap seals tightly to the metal flange/fill hole, metal flange fits tightly to the rubber filler tube although I added a ring clamp here to make sure, rubber filler tube was intact and sealed tightly to the metal tube coming up from the tank, metal tube firmly connected to tank. Side vent from rubber fill tube to evap box was firm, no leaks, good connections. Cleaned all of these and reinstalled and the fumes are better, not gone but much better. Did not remove and check the evap box as the connection from the box to the tube that runs up into the roof looked like it would be a nightmare to check and re-establish. Did note that there is a rubber cup/funnel under the outer flange/fill hole that connects to a tube that drops straight down into... nowhere, the area in front of the passenger rear tire, connects to nothing. I'm very careful not to spill when refueling so I dont think this is a problem, just surprised. Forgot to check the other connection from the box to the tank itself (3 lines from the box, one to the filler tube, one to the line that runs into the roof, one to the tank directly) at the tank, will do that tonihgt, I'm getting there. Did remind me however that I used to have a gas smell inside the car that was caused by gas spilled on the foam of the back seats (since repalced). Sometimes gas spills are hard to eliminate and it may be that there was some sort of spill in the trunk long ago.

  9. #9
    Fellow Frogger! julian b's Avatar
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    It is easy to check the funnell under the filler cap ,just pour some water into it and it should come out under the car where the rubber hose comes out

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