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boost guage needle postion 89T 700

posted by  Azureblue on  Thu Feb 3 04:34 CST 2005
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bringing this up from another thread---
My boost guage- 89T 740 auto- usually rests at about 9:30, and I gather this is a symptom of a vac leak. I am told it should be at about 8:00 postion on the guage. It's cold here, so I am not interested in spending too much time under the hood until it warms up a bit, so is there a way to isolate the culprit? And I gather the idle speed motor has something to do with it. Should I disable the IS motor until I find the problem?
Thanks in advance

R








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    boost guage needle postion 89T 700

    posted by  someone claiming to be bob on  Thu Feb 3 05:01 CST 2005 [RELATED]

    Idle speed motor has nothing to do with boost guage operation. There is a single hose coming off the manifold that runs inside the car, where it tee's to the boost guage and the overpressure switch. Look for a broken tee in the hose under the dash.








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      boost guage needle postion 89T 700

      posted by  Azureblue on  Thu Feb 3 07:35 CST 2005
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      I disagree: When the car is warming up, the idle speed control motor will raise the idle speed to 1000RPMs or a bit more, and allow in more air, and will raise the idle speed to 1000RPMs when the A/C is on. The vacuum changes can be seen on the vac / boost guage along with the RPM changes. At decel, the vac / boost guage drops almost to the peg, then the idle speed control motor will bring the idle RPMs back up to 750.
      Do I need to disable this thing before I go hunting for a vac leak?








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        boost guage needle postion 89T 700

        posted by  jmars on  Thu Feb 3 08:25 CST 2005
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        last visit: Wed Jan 2 02:18 CST 2008
        [RELATED]

        Instead of disabling anything why not find a way to draw a vacuum on the line without the engine running? A brake bleeder tool is what I use - you don't need much displacement to check a leak. This way you can start at the hose connection on the intake manifold and work back until you find the leak. Sure beats starting the engine over and over and disabling components and various systems.







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