Fuel Cap tighten message

Discussion in 'Engine & Drivetrain' started by latvius, Jun 13, 2018.

  1. latvius

    latvius Full Access Member

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    I keep getting the "tighten fuel cap" error alert. I used to have the problem of not able to fill gas tank. I have replaced the evap at the rear of the vehicle, the charcoal canister (blew out all the beads) and the one at the engine (dont remember the name of it). All this fixed my fuel fill problem. I also replaced the gas cap with an ac delco one.
    I put a smoker on it and the only place smoke comes out is at the rear evap (I think this is normal??).

    Assuming the smoke is supposed to come out the evap with engine off (I tried with key on as well) than I am at a loss on what to check next.
     
  2. Doubeleive

    Doubeleive Elite Member Supporting Member

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    Maybe try putting a factory gas cap back on it first, that's probably the cheaper option
     
  3. latvius

    latvius Full Access Member

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    Not sure if I have it still but I'll take a look when I get home.
     
  4. M1Gunner

    M1Gunner Full Access Member

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    Purge valve (intake manifold side) normally closed, Evap vent (fuel tank side) normally open. So, yes unless you manually close the Evap vent with a scan tool then it’s going to be open. UNLESS it’s running a monitor in which it will close the vent and the pcm will continuously monitor the fuel tank pressure sensor.

    When it comes to smoking the system, remove the schrader valve from the test port and use that to pump the smoke, DO NOT touch the gas cap, leave the vent valve open until you start to see smoke and then close the vent valve. The entire system should now be roughly filled, slowly check all lines from front to back. The reason you don’t want to disturb the gas cap is that it could be leaking and then when you fiddle with it the damn thing may seal properly.
     
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  5. latvius

    latvius Full Access Member

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    "remove the schrader valve from the test port and use that to pump the smoke" Is that schrader valve on the purge valve?

    "leave the vent valve open until you start to see smoke and then close the vent valve" Where is this vent valve?
     
  6. M1Gunner

    M1Gunner Full Access Member

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    The Evap test port has the green cap on it. Looks like a little green valve cap. It’ll be on the Black Evap line that runs to the purge valve that is on the intake manifold.

    The vent valve has to be commanded closed with a scan tool. It’s the Evap vent valve solenoid I believe is gm’s name for it.
     
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  7. latvius

    latvius Full Access Member

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    Gotcha, I don't have a scan tool though...
     
  8. easterr

    easterr Full Access Member

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    I replaced the gas cap, the solenoid near the rear axle and the valve on the engine and that fixed it. Replacing the gas cap alone, the easiest of the 3, did not fix it.
     
  9. easterr

    easterr Full Access Member

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    I now see you've tried all these also. Sorry.
     
  10. latvius

    latvius Full Access Member

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    np, I have done some searches but did not find my answer.
     

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