W900 air leak only when driving

Discussion in 'Kenworth Forum' started by redgod7, Feb 2, 2015.

  1. redgod7

    redgod7 Light Load Member

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    May 18, 2013
    Detroit, MI
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    Hi I have a 2007 w900 and it leaks air at 110psi and won't stop until I let off the throttle. Then it builds pressure normal and spits at 130psi like it should. Everytime it goes down to 110psi it leaks again. Usually if I'm light on the throttle it's just a quick hiss and goes away. Anyone know what it could be. I can't find no leaks when truck is parked.
     
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  3. JAL1972

    JAL1972 Bobtail Member

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    Feb 15, 2014
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    run the tractor only and see if leaks again. If not, at least you know the problem is in the trailer, and can pressurize the air lines at the shop and try to recreate the leak. Look at hoses moving while driving too. Tell us how's going.
     
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  4. Powder Joints

    Powder Joints Subjective Prognosticator

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    Sounds like maybe the dryer or govenor. Cant really say without having it here to check, this is where Id start the hunt.
     
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  5. Oscar the KW

    Oscar the KW Going Tarpless

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    Sounds like a purge valve, or possibly a unloader valve.
     
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  6. redgod7

    redgod7 Light Load Member

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    May 18, 2013
    Detroit, MI
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    I pull company trailers so I switch often. It's done it with everyone so far. The governor was my first thought too. I'm probably gonna replace it when I get back home. The hissing sounds like it's coming from the drier area but can't duplicate the problem when stopped.
     
  7. redgod7

    redgod7 Light Load Member

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    May 18, 2013
    Detroit, MI
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    Unloader and purge valve on the drier, right?
     
  8. Oscar the KW

    Oscar the KW Going Tarpless

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    Purge valve is on the drier, that's where the air gets spit out at. Unloader valve is in the head of the compressor.
     
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  9. redgod7

    redgod7 Light Load Member

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    May 18, 2013
    Detroit, MI
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    Thanks I guess I have some work to do this weekend.
     
  10. maggard359

    maggard359 Medium Load Member

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    Nov 20, 2013
    Florida
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    Boost leaking thru drier due to bad valve in compressor head. You will need to get a head kit for compressor or just exchange it. Drivable just let off fuel until compressor kicks off and it will stop.
     
  11. redgod7

    redgod7 Light Load Member

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    May 18, 2013
    Detroit, MI
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    So you're saying boost is leaking into my air system and forces purge valve to open? It sounds like you done that before. Is rebuilding the compressor top end an easy job? I do have plenty of tools from wrenching on cars. Wrenching on trucks is new to me tho. I just bought this truck last month and want to work all the kinks out.
     
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