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Finding evap leak

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  • Finding evap leak

    On my last smog, I failed the eval leak test. Anyone have experience in hunting this down? What methods or tools are best to tackle this?
    October 1987 build date.

  • #2
    You need a evap smoke machine tool. They arenít very expensive or hard to use.

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    • #3
      Originally posted by brandonsan View Post
      You need a evap smoke machine tool. They arenít very expensive or hard to use.
      I've run a smoke test in the past where I had it hooked up to my gas cap and it looked like all the smoke was coming out the bottom of my charcoal canister which I believe is open to the atmosphere. Do you think perhaps that win the tech is running this test he's not crimping the right hose that goes to the charcoal canister? Which hose that leads to the charcoal canister should be crimped to perform a smoke test to see if everything is sealed up?
      October 1987 build date.

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      • #4
        I thought the evap test for our cars amounted to only testing the fuel cap?

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        • #5
          The test hooks up to your gas cap filler and it's supposed to draw pressure from that system. I was under the impression that we have a hose going from our fuel tank to the carbon canister which in turn creates an opening to the atmosphere.
          October 1987 build date.

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          • #6
            Hi, the carbon canister is vents to the engine and is controlled by a solenoid, just can not recall when the solenoid energises allowing the canister to vent.



            E30 M3 1987
            Mini Clubman GT
            BMW E36 323 Msport
            Toyota Corona
            KTM 200EXC
            Honda CB50 (1979)

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            • #7
              Yes, there definitely is a venting mechanism. The solenoid operates when the throttle switch is in the running position (not closed, and not WOT). There might also be a time component involved (such as do not vent until x time elapses), but I'm not so sure of that.

              What I do recall from several years ago in CA was that the only thing tested was the seal on the gas cap. They'd remove the cap and thread it onto their machine and test the seal on the cap. Nothing else was tested. But maybe they've since improved their test to test the hoses and such. But at the time, none of that system was in scope for our cars.

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              • #8
                So help me understand how this test would work. The gas filler is plugged with the evap tester and the car needs to be in the on position to activate the carbon vent selenoid? Does the selenoid need to be activated to close the vent valve?

                When I smoked my car, sending smoke through the gas filler, the car was off and i could see smoke coming from my Carbon canister.
                October 1987 build date.

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                • #9
                  Are all the hoses at the canister hooked up? Some people disconnect the hose that goes back to the engine intake and plug it to keep the engine from dieseling after it is shut off. The european models essentially work without the canister, and plugging that hose is the equivalent. I believe the purge valve stays open allowing flow back to the engine for a few seconds after the ignition is turned off.

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                  • #10
                    All of my hoses are hooked up. I guess my question for the gurus here is whether or not is when the car is turned off is the path from gas filler to gas tank vent hose that leads to the carbon canister supposed to be completely open? From my example above, when I smoked my gas filler, I could see the smoke coming out the carbon canister. So that means with the engine off smoke went through the filler to the tank to the vent hose to carbon cannister.

                    Is that supposed to happen or is that hose supposed to be closed at the gas tank and prevent the smoke from leaving the gas tank and escaping to the carbon canister while the car is in the off position?
                    October 1987 build date.

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                    • #11
                      Hi I am not 100% sure on this but think what you described is correct otherwise normal heat expansion of the fuel tank contents, vapour would have no where to go and cause the tank to balloon out.
                      Some of the hydrocarbons must get caught up in the charcoal and when the engine starts solenoid opens (or closes) then air is drawn through the vent area on the canister through charcoal removing the hydrocarbons and then in to the engine?

                      E30 M3 1987
                      Mini Clubman GT
                      BMW E36 323 Msport
                      Toyota Corona
                      KTM 200EXC
                      Honda CB50 (1979)

                      Comment


                      • #12
                        Thank you for the reply. Can anyone confirm? If this is the case, the a gas filler evap test will always show a leak! I'm deciding options here, i wonder if I research how am evap test works at this point, and determine if a test like this is not possible on our cars then.
                        October 1987 build date.

                        Comment


                        • #13
                          My little 1990 325ic failed the CA smog today. Same issue as this thread. I asked the guy EXACTLY what the test is. He takes a compressor and pressurizes the gas tank and looks for leaks. The takes a long need nose pliers and reaches down and clamps off the cable at the evaporator, then does the pressure. He said that it is like a rubber fitting near the gas filler. He said some people put smoke in the tank and see where it comes out. Did you guys ever figure out where your leak was, and what you did to fix the issue?

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                          • #14
                            When i ran a smoke test for my car, the smoke was pouring out of the charcoal canister, exactly how it should. I suspect when i failed the evap test that the technician didn't properly crimp the tube leading to my charcoal canister to get a good seal. It will still be an issue for the next smog and i need to find a technician who can test my car prior to smog.

                            In the past i never had anyone test the evap system, they will just put n/a for that test and this last time was the first anyone actually did it. It appears as if some of our fellow Cali members have stations they know about that don't do this test, maybe they can share?

                            Originally posted by tdennehy View Post
                            My little 1990 325ic failed the CA smog today. Same issue as this thread. I asked the guy EXACTLY what the test is. He takes a compressor and pressurizes the gas tank and looks for leaks. The takes a long need nose pliers and reaches down and clamps off the cable at the evaporator, then does the pressure. He said that it is like a rubber fitting near the gas filler. He said some people put smoke in the tank and see where it comes out. Did you guys ever figure out where your leak was, and what you did to fix the issue?
                            October 1987 build date.

                            Comment


                            • #15
                              Close off the bottom of te char coal canister so smoke can no longer escape there. At the same time energize the solenoid so the smoke can pass on to the intake manifold and exit at any leak along the way thereby showing where said leak is.

                              Another way is to open the Throttle bodies hook up the smoke machine to one or all of the ports that are used for syncing the throttle bodies and watch where smoke exits on its way to the charcoal canister

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