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Thread: Raw Gas Smell Inside the Car While Driving

  1. #1
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    Default Raw Gas Smell Inside the Car While Driving

    Before everyone burns me up about using the search feature, I promise you that was the first thing I did. I used several posts to help me search through and check the connections at fuel pump, tank, expansion tank, filter, fuel rail and everything in between. All connections are tight, no hoses are ripped or failing, and there's no evidence of any gas leaking anywhere. So why is there such a crucial raw gas smell while driving?

    It only happens when the car is driving and typically at decelleration. Doesn't have to be after a hard accelleration, but take your foot off the gas and the cabin becomes full of fuel smell. I can't smell it at any other time. I can't get the car to recreate the smell by revving it while sitting in the driveway.

    Any ideas what I should look at or how to make it happen while not driving so I can try to identify the source of the smell?

    This is a suddenly new issue that we hadn't ever experienced through the many years of owning the car. Exhaust smell has been an issue, but whatever, it's an old car. However the fuel smell is so strong there's no way to ignore it.

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    The BCDD system is designed to clean up the exhaust from excess HC (unburned fuel) under certain conditions. there's actually a little gizmo on the speedometer that measures road speed, and engine speed is involved too. Has anything else malfunctioned or have you modified some things?
    1976 280Z, with some minor modifications

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    Zed,
    We had done some mods recently which I had a post going for a while because we had a terrible time getting proper fuel pressure after the mods were done. We swapped to a non-egr intake and palnet fuel rail. We installed new injectors, FPR, pump, filter, and hose. When the car was getting warm it would lose power almost completely leaving us stranded a couple of times. Let it sit and cool off and we could drive it for a short period of time again. It was losing fuel pressure. In the end it turned out to be that we forgot to fill up the coolant after the intake swap so the temp sensor was getting some nasty info that had seriously negative affects on the car.

    Anyway that's been remedied and the car is running great, however we're left with this raw gas smell that we can't find the source of. Hopefully that gives you a little insight into our history and might help you to lead me in the right direction.

  4. #4
    Z geek at large FastWoman's Avatar
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    I would two general sources:

    (1) Gassy exhaust smell entering the cabin through rotted or misfitting hatch seals (or rust hole in body).

    (2) Problem with fuel tank ventilation system or filler neck. It's possible you have a leak in one of your vent hoses, such that when the gas sloshes just right, you get a little glurp of raw gas inside the car, behind your rear passenger trim panel (where the fuel/air separator and filler neck run). If you haven't replaced all of those hoses, you should. Also check the nipples on your fuel/air separator (the big, irregular can-like thing behind the trim panel). Mine had a cracked braze joint one one of the nipples that sometimes leaked raw gas.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Nova Scotia,Canada,Earth Blue's Avatar
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    I concur with FastWomen #2
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

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  6. #6
    Registered User madkaw's Avatar
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    I had some success with my 71 system by pressurizing the vent system and looking for leaks with some soapy water. Use very little pressure.
    I hooked up air at the vent line that is in the engine compartment .
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Can you tell me which line in the engine compartment is a vent line? I'd line to try pressure testing the system that way as well.

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    Z geek at large FastWoman's Avatar
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    It's the one that goes to the carbon canister.

    BTW, don't apply much pressure. Remember that it's a large tank.

    Besides that, there's a weird little check valve between the vent system and the carbon canister. It actually flows two ways, but it flows easily in only one direction. That might make it difficult to pressure test from the carbon canister connection.

    If I were you, I'd just replace the hoses for peace of mind. If they're as old as the car, then they're due.
    Last edited by FastWoman; 09-20-2014 at 11:20 AM.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Registered User madkaw's Avatar
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    Please only use enough air to fill the system. I think I had 10psi set on my airbrush compressor.
    Good luck
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  10. #10
    Registered User siteunseen's Avatar
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    On my '77 there's a round plate covering the fuel gauge sending unit in the hatch, by the spare tire. 3 screws I think to remove it and check to make sure the sending unit is locked in place. It also has an o-ring that could be missing or distorted.
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    Registered User txvepr's Avatar
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    Are you sure its gas and not exhaust? As Z drivers we get to become aficionados on the subtle differences!
    Another thing I have found it the rear wheel wells will have seams that have opened up. Put a drop light under neath in the well, and then open the back and remove the interior panels and look for light. I had to reseal them with RTV or silicone and it helped alot.

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