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Recirc vacuum leak? Whistling 900

posted by  The Rod on  Mon Dec 9 14:25 CST 2013
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last visit: Fri Oct 17 12:15 CST 2014
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I just broke out my older 940(94 NA) and to my dismay noted a whistling sound in dash when accelerating or deccelerating right around 30-35 mph Sounds like the whistling noise you would hear in cartoons when they drop a bomb and you hear it whistling high pitched and getting lower as it approaches the ground. Sorry only way I can think to describe. FAQ's seem to point to Recirc vacuum motor. Any experience the whistling in conjunction with such a failure?








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    Recirc vacuum leak? Whistling 900

    posted by  HillBilly on  Tue Dec 10 09:22 CST 2013
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    last visit: Thu Oct 16 08:26 CST 2014
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    My guess is that you have a crack in a rubber vacuum hose inside the dash.
    Either that or one of the vacuum operators has a small leak.

    To trouble shoot, I install a vacuum gage in the vacuum hose that's located on the firewall.
    This line has a vacuum check valve installed and goes to the heater controls under the dash.
    The check valve looks like a small Oreo cookie with a small rubber hose into and out of it.
    Place the vacuum gage in the rubber line on the heater side of the check valve, that way, the check valve will hold vacuum on the system after you stop the engine.

    Watch the gage after you stop the engine.
    If it leaks down, you have a vacuum leak in the line or under the dash.

    Hope this helps
    steve








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      Recirc vacuum leak? Whistling 900

      posted by  The Rod on  Tue Dec 10 09:34 CST 2013
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      last visit: Fri Oct 17 12:15 CST 2014
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      Thanks for the reply Steve. I would go and borrow a vacuum tester today, but for the fact I already know I have a leak. I got lazy yesterday and failed to mention that if my fan is set to blow at head level and I accelerate it switches to blow at my feet. Classic symptom per the FAQ of a split line or failed vacuum servo. I have simply ignored it for years as I only use A/C once or twice per summmer. I am only chasing the "source" of the leak now(because the noise annoys me :). FAQ's point to a split line or servo, just looking to see if anyone else has had a significant whistling with said leak in hopes of pointing me to one location. I am resigned to getting up under there and looking around this weekend. Its a shame you cant do a "smoke test" on the vacuum lines to pinpoint the leak. TTYL.








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        Recirc vacuum leak? Whistling 900

        posted by  Amarin on  Tue Dec 10 19:37 CST 2013
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        last visit: Thu Oct 23 22:42 CST 2014
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        Hello,

        Have a look at the plastic vacuum hose coming out of firewall just below the distributor. Be VERY gentle in handling this as the hose might also crack during checking. The hose became hardens after being exposed to exhaust heat all this while. A leak could be there.

        In my case the plastic hose was cracked. I repaired using the usual flexible vacuum tubing all the way to the 'Oreo' valve. The symptom was the vent blows to the floor during accelerating. But there was no whistling sound inside cabin.

        In your case I think the rubber diaphragm in one of the vacuum servos might have a leak producing the sound you've described.

        Hope this helps.

        Amarin.








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          Recirc vacuum leak? Whistling 900

          posted by  The Rod on  Wed Dec 11 09:59 CST 2013
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          last visit: Fri Oct 17 12:15 CST 2014
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          Morning
          Thanks for the reply. What is the "distributor" you speak of? Would I be best able to see it on the passenger side or the drivers side? Do I need to remove anything to see? I am quite comfortable removing the radio and climate control if need be. I will be chasing this weekend.








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            Recirc vacuum leak? Whistling 900

            posted by  Amarin on  Wed Dec 11 12:49 CST 2013
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            last visit: Thu Oct 23 22:42 CST 2014
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            Hello,

            The distributor I'm referring to is the ignition distributor inside the engine compartment where all the spark plug wire goes into. In my case the leak was inside engine compartment. But in your case I think the leak is in the cabin which involve the vacuum servos.

            A helper is needed I think. First you need to remove the covers underneath the dashboard. Drive around with acceleration or drive uphill with someone to locate the whistling sound.

            Hope this helps.

            Amarin.








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              Recirc vacuum leak? Whistling 900

              posted by  HillBilly on  Thu Dec 12 09:33 CST 2013
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              last visit: Thu Oct 16 08:26 CST 2014
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              You can also use a small manual vacuum pump.

              Pump up the vacuum on the back side of the check (Oreo) valve and look for the leak at your leisure.

              Something like this.
              Every shop should have one.
              http://www.harborfreight.com/mityvac-vacuum-pump-39522.html

              steve







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