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Evap system repair from manual

Discussion in '1st Gen. Tacomas (1995-2004)' started by Bruciebbb, Oct 9, 2019.

  1. Oct 9, 2019 at 11:57 AM
    #1
    Bruciebbb

    Bruciebbb [OP] New Member

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    I have a 2001 2.7 tacoma. I have been fighting the dreaded p0446 all year. Its emmisions time and i cant get it to pass. I am at the end and ready to take it to the dealer . Ive tried every test i can find on the internet to find something wrong. Everything so far works. I think i need the Toyota repair manual portion that has the evap system testing. I found the whole manual on this site but the evap portion doesnt work. Does anyone have the complete tests to perform to find the problem. Ie, what ports to block and which ones to test. I can do air or vac tests. Im missing something and it is getting frustrating
    Thanks
     
  2. Oct 9, 2019 at 9:12 PM
    #2
    Glamisman

    Glamisman Well-Known Member

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    You might be looking in the wrong spot. IIRC... The sole purpose of the VSV, Vacuum switching valve, is to shut off the vacuum signal from the engine to allow vapor pressure to build up in the fuel tank and the related hoses etc. If this can't be done due to leakage the VPS, vapor pressure sensor, will signal that there is an issue. Fuel cap is the first and easiest to replace. Some peeps have had good luck with aftermarket ones but after you have spent hours and hours looking for a pin hole leak the $ spent on a Toyota gas cap is well worth it.

    I assume you have a OBDII scanner and can clear the codes, if not, you are wasting your time. If you do, I would clear any codes and plug the lines from the VSV and drive her around. This should allow pressure to build in the fuel tank/system. If the code still pops you are going to have to get her smoke tested or apply a vacuum source from a hand vacuum pump and see how long it takes for the vacuum to drop. The time it takes is going to tell you if it is a big or little leak. The problem is the stuff you want to get to is on the top of the fuel tank and that can be an issue. Apply vacuum to the line plug the other end and see if it leaks, if no leak, go to the next line and repeat. You are either going to find it immediately or hours later... there doesn't seem to be any intermediate step. Best money might be spent on a smoke test with a good tech. This could be the VPS, the fuel filler tube or the fuel tank.

    There is something else to consider... the tests for the evap portion of the drive cycle only happens when a defined set of parameters are met. Fuel tank between 1/4 and 3/4 full, the Intake air temp sensor and the engine coolant temp sensor with in a few degrees of each other and the truck hasn't been started for apx 8 hrs and this has to happen twice.

    I have attached 2 files. These are from a 2000 tacoma factory manual but the tests should be close enough.

    Good luck sir.
     

    Attached Files:

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  3. Oct 10, 2019 at 2:56 PM
    #3
    Bruciebbb

    Bruciebbb [OP] New Member

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    Thank you for helping. Not having a complete manual to tell me the logic of this system makes it hard to work on. Ive tested both vsv's and they seem to work. I applied vacuum to the purge port and covered the air in port and it holds vacuum. I figured that would include the whole system. Can the vac sensor be tested. I hate to just throw money at it for no reason. Every test ive read to do shows nothing wrong. If i apply vacuum at the tank vent hose should it hold vac? When you say plug the vsv, you mean the purge solenoid right? Wouldn't i get a code saying thats not working. Everyone also uses a few different terms for the components, that makes it difficult. This thing is consuming me and i just dont get it. I would love to find something wrong
     
  4. Oct 10, 2019 at 3:18 PM
    #4
    RysiuM

    RysiuM Well-Known Member

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    Sorry to hear that. EVAP system is a bitch to diagnose. Especially when the code will pop-up after many different driving cycles so you can't just see stuff working like "live data" on the scanner. So the only way to diagnose it is check each component for functionality and making sure there is no leak. And inspecting those components sucks because they are in difficult to access places (fuel tank, canister, rubber hoses).

    I feel your pain as I was chasing "small leak" in Sienna I used to own. It was popping up and disappearing for weeks. Replaced VSV, fuel cap and nothing. I even bought a vacuum testing set from HF. Finally I took a charcoal canister out (in Sienna it was relatively accessible) and run a diagnostic procedures as described in FSM (block these pipes, blow this and see if air goes that pipe). One test failed. When I cut the canister open one of the diaphragms was cracked. New canister shut up that "small leak" forever.

    Not saying it is a case in your truck, just saying you have to run all tests on individual components to see which one is failing.
     
  5. Oct 10, 2019 at 6:59 PM
    #5
    Glamisman

    Glamisman Well-Known Member

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    IIRC and if I am wrong someone please chime in... it is my understanding that certain states allow for one smog monitor to be incomplete and this usually the evap system monitor because of the difficulty of it. If this is the case and your state allows for one monitor to be incomplete and you have a OBDII scanner that shows which monitors have run, completed and passed, I would always drive on a full tank so that that monitor will never start. If the CEL is out and there is only the evap monitor to run you should pass the inspection. There is a breakpoint around 2000 - 2001 where you can get away with one monitor not running as opposed to all have to have run and passed. I understand that this is "gaming" the system but there are other things more important in life than smoging a truck.


    I was You Tube surfing and I came across a posting on the "South Main Auto Channel" where he has a 03 Chevy truck with a P0446 code. He goes into detail about his thoughts and his diagnosis... this was a 2 part problem. He shows where the vacuum reading that the vapor pressure sensor is sensing is tripping the CEL due to the charcoal canisters charcoal... it has turned into mush and not allowing the vacuum to drop when the VSV valve opens. It is worth the time to watch it.
     
    Last edited: Oct 11, 2019
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  6. Nov 27, 2020 at 11:41 PM
    #6
    RockRat

    RockRat New Member

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  7. Nov 28, 2020 at 5:20 AM
    #7
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Stock. EZ pass.Dump pass.Inspection sticker.Convict printed lic.plates.FG cap.
    Focus on Purge Selnoid, fuel tank Vapor pressure sensor and switch.
    I have tested VSVs that checked out but worked intermittently causing P0446. Purge Selnoid was the culprit.
    20 year old $90 switch and $30 thick wall Silicone Vac lines CEL light went off on its own.
    Screenshot_2017-10-15-10-28-54.jpg
     

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