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Thread: Gas vapor smell while driving.

  1. #11
    Senior Member DMCVegas's Avatar
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    Quote Originally Posted by Rich View Post
    ++ See Dave's post #4. Your charcoal canister vent hose and the fuel filler neck should have a direct and normally-open connection, one that prevents pressurization of the tank. A simple air flow test from the canister connection forward with the fuel cap off will verify satisfactory venting or troubles from blockage.
    Umm, yes and now. Quick and dirty explanation:

    When the car is at rest the Charcoal Canister collects fuel vapors from the fuel tank. There is then a tube that connects to the Intake Manifold, BUT there is a diaphragm controlled valve that keeps that particular tube closed while the engine is at rest. Once the engine starts, vacuum will be applied to the diaphragm causing it to open. Engine vacuum then takes over and evacuates the accumulated fuel vapors from the Canister. The only difference between older cars like the DeLorean and any modern one is that the vacuum line has since been replaced with a solenoid valve.

    So yes there is a constantly open tube, but ONLY when the engine is running.

    HOWEVER it should be noted by everyone that Canisters can in fact malfunction if exposed to raw, liquid fuel. They will clog up and prevent the unit from purging once the engine starts. This is key to maintaining the fuel pump as well as to prevent vapor from leaking out. I've had this same problem with my own DeLorean. I replaced the Charcoal Canister and it went away. I also had a Jaguar XJ6 that had this EXACT same issue. Fuel pump would buzz, and there would be a strong smell of gas at the back of the car. Pop the cap off and you would hear the pressurized vapor escape and then the car would be quiet again. Hell even at my last job we had a memo sent out about this same issue. Lots of field techs were complaining that their trucks had strong gasoline smells. They ended up dropping several thousand dollars at the local Ford dealer to get all those canisters replaced because the techs were topping-off and causing liquid to contaminate the charcoal canisters.

    You don't normally see this issue with cars simply because the fuel cap is aft of the windshield, so the vapors simply get blown away. But if you're ever stuck in traffic and are nowhere near any gas stations and smell that strong sickly-sweet hot petrol vapor, you know that someone's car around you has a failed charcoal canister. Even California has since taken to testing these components since ODB-II can't detect the problem. The DeLorean is excluded of course because our canisters are not readily accessible for testing.

    If you're ever wondering if you've got a bad Charcoal Canister and want to test it, it's simple, but it's best done on a hot summer day.

    1. Remove your gas cap. A little pressure hissing is normal. But if it sounds like a deflating balloon, you've got a problem.

    2. Disconnect the Vacuum Hose, then plug it up. Connect a hand-held vacuum pump to the Canister and start pumping, You should see a change in the engine's RPMs right away. If not keep pumping. Apply enough pressure to get the valve to crack open. Once it does you'll hear the engine go crazy as the LAMBDA system goes haywire trying to adjust the fuel mixture. This method will tell you if it's just the diaphragm that's bad, but either way you're going to be replacing that canister since it's a non-serviceable part.

  2. #12
    Senior Member WelmoedJ's Avatar
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    Quote Originally Posted by DMCVegas View Post
    2. Disconnect the Vacuum Hose, then plug it up. Connect a hand-held vacuum pump to the Canister and start pumping,
    Call me stupid, but....
    The canister has three vac lines, which one you refer to for disconnection?
    Which of these lines you intend to use to crack open?

    Or do you mean "take out the canister and then test?
    But even then which are the connections to use?
    And what does one do with the remaing connections/lines ("plug the vacuum hose")?

    Thanks for explaining.
    Welmoed
    Black D 1981-11 sold
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  3. #13
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by Nicholas R View Post
    Make sure your sending unit cap is tight, very tight. I drove around with that smell for a few years, turned out my cap was just dirty and wasn't compressing the fuel sender gasket so when the gas would slosh around, it would leak out there.
    +1 here, I had a bad gas odor as well and this was my problem. The gasket has a notch that must line up with the tank as well as the sender, and whoever installed mine last did not line them up. Small amounts of gas were sloshing out and the smell was pretty strong. Removing the sender, cleaning up the mess and reinstalling it with a proper seal eliminated the odor completely.
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
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  4. #14
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    Before going through a lot of testing check the vent hose that comes out of the bottom of the vapor canister. I see them plugged up with insect cr-p all the time. Stick a wire up inside. The hose should be sticking out of the bottom of the driver's side pontoon. If it isn't you will have to open the pontoon and route the hose properly. I would still start at the fuel tank and check all of the components there first. A little pressure is normal on the tank, especially if you park it outside and the car gets hot.
    David Teitelbaum

  5. #15
    Senior Member QuadcityDMC's Avatar
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    I took that cover off today and found nothing twisted or bent. No fuel leakage around the tubes. Is it possible that I might have a bad seal on the gas cap?

    I did find a hole in the body tube, looked like someone tried to add another trunk cable and drilled into the back of some wires but stopped short.

  6. #16
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    You should at least remove the cover boot and make sure there is no fuel in the pump boot. If everything is nice and dry you will have to look elsewhere. Make sure the tank sender is sealed. If all of that is good you will have to follow the vent hose to the vapor cannister to make sure it is not kinked, blocked, or cut.
    David Teitelbaum

  7. #17
    Senior Member QuadcityDMC's Avatar
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    I took the "vapor" hose off the roll over valve and to the carbon can out to see if any thing was up with it.





    This is what it looked like when i took it out, the bottom was off and a hose was not connected. I took the hose to the tank off and checked it. It was clear but I did cut the hose off at the 90 because it was leaking through the hose.

    I connected all the hoses back and but the bottom on the carbon can. Checked fuel pump boot, which has new DMCMW hoses. I will have to drive around and check again if there is any leaking from the pump. Gas tank is 1/2 right now.

    Going to order a new gas cap also.

  8. #18
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by QuadcityDMC View Post
    I took the "vapor" hose off the roll over valve and to the carbon can out to see if any thing was up with it.

    This is what it looked like when i took it out, the bottom was off and a hose was not connected. I took the hose to the tank off and checked it. It was clear but I did cut the hose off at the 90 because it was leaking through the hose.

    I connected all the hoses back and but the bottom on the carbon can. Checked fuel pump boot, which has new DMCMW hoses. I will have to drive around and check again if there is any leaking from the pump. Gas tank is 1/2 right now.

    Going to order a new gas cap also.
    Well time and your checks will tell, but I'd be willing to bet you found your problem. I didn't know the bottom could come off the canister. I wonder if it might be up for replacement, but others may have more info than me on that.
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, March 2011 to present
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  9. #19
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    The bottom comes off so you can get to the filter to replace it.
    David Teitelbaum

  10. #20
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by David T View Post
    The bottom comes off so you can get to the filter to replace it.
    David Teitelbaum
    Learned something new today. I didn't know it had a replaceable filter, I thought the whole canister was a sealed throw-away unit. Good to know!
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, March 2011 to present
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