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98 TA fuel smell coming out of the fuel tank neck/cap

This is a discussion on 98 TA fuel smell coming out of the fuel tank neck/cap within the General Help forums, part of the LSx Technical Help Section category; Hi guys. I have been dealing with this issue for almost a year and it is getting worse. If I ...

  1. #1
    Senior Member JayTA98's Avatar
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    1998 Trans Am

    98 TA fuel smell coming out of the fuel tank neck/cap

    Hi guys. I have been dealing with this issue for almost a year and it is getting worse. If I take a long drive and park the car in the garage or when I step out of the car I can smell fuel. It only happens when I drive the car for a long time. Doesn't matter if the tank is full or half. You can see the fuel cap gasket damp with fuel.

    Today I filled the tank and drove for about 1.5 hrs mostly highway. I didn't dripped any fuel on the side of the car and the fuel cap was dry when I finished fueling. During the few stops on the way as soon as I opened the door I can smell the fuel odor. When I got home I noticed a fuel stain on the side of the car underneath the fuel door. I heard this hissing noise and I confirmed the noise is coming from the fuel cap area. there is pressure building in the tank. I removed the fuel cap and heard the pressure release. I put the cap back on and after a minute I can hear it hissing again(not as loud). This happened after I just got home from driving, as the car sits out longer the hissing noise stops.

    I have replaced the fuel cap 3 times in an attempt to rule out a bad cap but it hasn't work, so I know is not the fuel cap.
    During my research I have found information about other possible causes. It could be the EVAP purge solenoid not working, a clogged EVAP hose, bad EVAP canister(rare) or fuel tank vent valve.

    I'm going to check the evap hoses. I'm not sure if I should start by replacing the vent valve or the evap purge solenoid. Any suggestions?

    I have found the fuel tank vent valve on gmpartsdirect.com but I don't know the part number. Does anyone know the part numbers of the evap canister, evap purge solenoid and fuel tank vent valve? Thanks.

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    Junior Member tekkauto's Avatar
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    Mystic Teal
    1999 Formula WS6

    Do you have a service engine soon light on? If you do then there could be a failed evap vent valve or purge solenoid. These two items are monitored by the pcm and will set a fault code. If you DON'T have a service engine soon light on then there is a possibility of a plugged or failed charcoal canister or a pinched evap hose/pipe. If you take the car to a gm dealer they do have the proper test equipment to find out where the problem is at. It's obvious that your evap system isnt venting properly. Throwing parts at it isn't the way to go because most of your evap system is located on top of the fuel tank and is hard to access.

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    Senior Member JayTA98's Avatar
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    no SES. I will take to my friend mechanic since it will be way cheaper than going to GM. I did checked the lines going to the evap canister and the one going to the evap vent valve is clear. I actually blew thru it and I can feel the air out coming from the evap vent valve so I know it is clear. I did the trap door years ago so I need to check the line from the tank to the canister. I did pull the line out at the canister and immediately smelled fuel. I have to checked the evap purge valve tomorrow after I take car for a drive to test if it is opening.

    I'm suspecting the canister is clogged because the line coming from canister to the evap vent valve is open when the car is off so the tank should be venting thru there. If the line from the tank to the canister is clear then I believe the canister might clogged. I think there is a filter inside of it.

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    Junior Member tekkauto's Avatar
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    Mystic Teal
    1999 Formula WS6

    To the best of my knowlege there is never a filter inside a gm canister. I see cars and trucks come into my shop every day with plugged canisters due to gravel road dust (may sound crazy but in rural Minnesota, most roads are gravel, not paved). This typically causes fuel spit-back or gas pump shut off when filling. There is a slim chance you could try blowing out the canister with compressed air but usually it does not work. If the canister is restricted, replace it. Also, the vent soleniod is normally plugged when a canister is plugged, but that should turn on the ses light with a P0446.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by tekkauto View Post
    To the best of my knowlege there is never a filter inside a gm canister. I see cars and trucks come into my shop every day with plugged canisters due to gravel road dust (may sound crazy but in rural Minnesota, most roads are gravel, not paved). This typically causes fuel spit-back or gas pump shut off when filling. There is a slim chance you could try blowing out the canister with compressed air but usually it does not work. If the canister is restricted, replace it. Also, the vent soleniod is normally plugged when a canister is plugged, but that should turn on the ses light with a P0446.
    So does it makes sense to you that if the canister was not clogged it should be venting fine? I checked the canister vent valve tube. when I disconnect it and I blew air thru it comes out with no restriction at the end of the vent exhaust. If I suck air in the canister vent valve tube I have no restriction either. Is the canister vent valve supposed to be open when the engine is off? I think it should stay open when the engine is off and then it fluctuates when driving around.

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    Senior Member JayTA98's Avatar
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    If I pull the canister and I blew thru the ports. It should allow air with no restriction thru all the ports, right?

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    Junior Member tekkauto's Avatar
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    Mystic Teal
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    If you blow air thru the canister, It will not prove weather or not it's plugged. Thats why I am referring you to a gm shop that has evap pressure testing equipment. Most independent repair facilities don't have this machine. It flow-checks the evap components using pressure. The canister can be a bit of a mystery to test. It sounds like the canister may be your problem but I'm not sure. I'm not sure if the vent valve or purge solenoid shoud be open or closed when the engine is off, but If I get a chance I can check the service manual tomorrow. I would guess they should be closed in order to monitor for evap leaks?

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    Senior Member JayTA98's Avatar
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    I agree with checking to make sure of what's wrong 1st before start buying stuff. the problem is that the gm dealers here charge an arm and a leg. even if I buy all three parts together I believe it will be cheaper. I qouted $150 for all parts from rockauto. the expensive one is the canister. I have a local place that parts our cars. I might call and see how much an used charcoal canister cost.

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    Senior Member JayTA98's Avatar
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    I got an used charcoal canister and canister vent valve for $5 at my local place that parts out fbodies. I installed the canister 1st. I will update my results

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    Senior Member JayTA98's Avatar
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    It seems the used canister and used canister vent valve did not help. I just put the EVAP purge valve. I'm wondering if the tank wasn't venting correctly if it could have damaged my fuel cap. It keeps leaking fuel by the neck every time I drive around. The tank is 3/4 full.

    I disconnected the lines and blew compressed air from the purge valve (by the engine) to the back, from the back to the canister. I also did from the canister to the canister vent valve. All of these were clear. There was no resistance and I can hear the air coming out at the end.

    I did from the canister to the fuel tank and I can hear it bubbling with a little resistance but I figured it should be normal since the air is exiting under the fuel level inside the tank.

    So my understanding is that the lines are not obstructed. I guess if after the fuel cap I doesn't get better I will have to take it to the dealer.
    I'm also wondering if the filler neck is not sealing with the fuel cap gasket. IS there any type of grease or sealant I can use to test this out?

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    Moderator Cutlass's Avatar
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    I have seen this before...one time. And I can't remember what fixed it. I'll have to ask the guys are work and see if anyone remembers. I'm kinda surprised the gas caps, vent valve solenoid, and canister haven't fixed it. Those would be my top 3 fix ideas for sure. Purge valve solenoid valve is another good idea. If its not working, it can't suck the fuel vapors out of the tank and canister. Eventually the canister will become saturated with vapor (resulting in liquid gas) and cause your same problem.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by Cutlass View Post
    I have seen this before...one time. And I can't remember what fixed it. I'll have to ask the guys are work and see if anyone remembers. I'm kinda surprised the gas caps, vent valve solenoid, and canister haven't fixed it. Those would be my top 3 fix ideas for sure. Purge valve solenoid valve is another good idea. If its not working, it can't suck the fuel vapors out of the tank and canister. Eventually the canister will become saturated with vapor (resulting in liquid gas) and cause your same problem.
    Thanks for the response Cutlass. I think I might find out what the issue ia. I'm still testing but I had a suspicion about this a long time ago. Since I replaced the OEM original gas cap that came with car I started having issues. I don't have the OEM cap anymore (since I tossed it out) but I did noticed it was a little different from the new ones.

    The first thing made start thinking about it was every time I tried to order a gas cap for a 98 the majority of the local places will not have a replacement part in their system but it will have one for 99-02. 98 is the only year that has the metal tank with metal fuel neck(if i'm not mistaking). What I have noticed in all the replacement caps I had bought(3 to be exact) is the gasket feels like is not sealing tight enough. There is a plastic ring in front of the gasket that is part of the plastic in the cap. This ring stops the cap from going too far in the fuel neck.

    Since I had a spare gas cap (that I marked as bad because it never fixed the issue) I decided to pull the gasket and with my dremel tool get rid of this plastic ring. My reason behind this was if the ring was gone it will allow the cap to set in deeper. This will cause the gasket to seal tighter. I put the gasket back in the gas cap and tested the fitment. I immediately noticed and heard the gasket making better contact with the fuel neck. It had enough pressure to hold it in place and the cap comes off normal.

    I cleaned all the residual spilled fuel. I took 3 trips today and I have not noticed any more fuel spilling. No fuel smell in the garage either. It is early for me to say it is a fix but it makes sense if the gasket was not sealing properly.

    I will put some picks later once I confirm this fixed the issue. If anyone has an OEM gas cap can you please post a picture of the side and inside of it? It will help me visually confirm the difference. Thanks.

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    Senior Member JayTA98's Avatar
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    Oh I forgot to mention the purge valve was working. I pulled the hose out and I can feel the pulsating vacuum.

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    Senior Member JayTA98's Avatar
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    well so far no leak coming from the fuel cap. I do still get the vapor smell when I fill the tank up and take a long drive on a hot day. I hae to check the fuel pump gasket to make sure is not leaking from up there. It shouldn't. It sounds like the car it is still venting but I tought the vapor go thru the charcoal canister before the vent valve. So the canister should collect the fuel vapors.

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    Smiles for 9.5 Years cammed goat's Avatar
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    For some reason, I'm thinking fuel tank vent valve. When you tank up the car, do you have any issues with the nozzle popping early as if the tank is full?

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    Senior Member JayTA98's Avatar
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    well the tank valve I believe is over pressure as a safety device. the regular canister vent valve should vent the tank normal but it has to thru the charcoal canister before the vapors exit the valve. so the canister should filter the fuel smell. I changed the canister but it was for an used one. not sure if the canister is bad but it sounds like a coincidence that both are bad.

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    Smiles for 9.5 Years cammed goat's Avatar
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    Any updates?

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    Senior Member JayTA98's Avatar
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    it has not happen again. im trying to make sure it was not residual left over from the previous spill and when it got hot it would smell. if I notice the smell I will check the lines.

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    expensive tires az gt eater's Avatar
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    So, it was the cap? I was trying to follow, and it seemed like that was your problem.

  20. #20
    Senior Member JayTA98's Avatar
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    Quote Originally Posted by az gt eater View Post
    So, it was the cap? I was trying to follow, and it seemed like that was your problem.
    Well initially it appeared to be a cap issue and it was. I have been dealing with the cap not fitting right on my car for a long time since i replaced the original. I ended up altering it. It fits and seals fine no more leak. Like a week later i tool the car out on a hot day, i filled the tank and drove for about 1 hr. I got home and put the car in the garage. About 30 mins I decide to go in the garage and I smelt the fuel vapors again. I checked the fuel cap and fuel neck(where it normally leaks) and there was no leak.

    I did noticed alot of leaft over split on the fuel tank neck so it made me wonder if when it gets hot it wound smell. So far it has not happened again. It seems it happens only in very hot days. The weather is cooling off now but i will keep and eye on it.

    Before with the cap that was leaking I will hear the vapors leaking thru the cap seal, like the tank was over pressurized. I only noticed that once.

    I will post pics of the cap mod I had to make today .

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