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'88 760 Turbo vacuum question... (261,000) and going strong... 700

posted by  vincentfc on  Wed Oct 6 09:42 CST 2004
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last visit: Fri Jul 20 10:32 CST 2012
[RELATED]

When I have the blower switch on and driving normally (out of turbo range) the blower motor operates fine... When I step on the gas the blower motor decreases in output and at times completely stops until I let up off of the gas pedal... When I let up off of the gas pedal I hear a 'popping' sound like a vacuum switch is closing (or opening)...

I'd appreciate any guidance on determining what specifically is wrong and how to repair this...

Thanks,

Frank








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    '88 760 Turbo vacuum question... (261,000) and going strong... 700

    uid 55's pic
    posted by  john sargent on  Sat Oct 9 10:35 CST 2004
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    last visit: Wed Oct 22 09:07 CST 2014
    [RELATED]

    I experienced the same problem on our 1988 760T. On our car, the vacuum leaks were at the engine where the vacuum check valves are. I installed worm drive clamps to seal the old hoses better. Problem solved. See the clamps in the picture.

    --
    john








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      '88 760 Turbo vacuum question... (261,000) and going strong... 700

      uid 27's pic
      posted by  Art Benstein on  Sat Oct 9 14:06 CST 2004
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      last visit: Fri Oct 17 20:10 CST 2014
      [RELATED]

      Neat trick, John. Just this month I've found two of our non-turbos have defective check valves, made evident by the wheezing sound from inside. Couldn't find them on-line, so I visited the junkyard. Interestingly, to me, the three I pulled there were all fine. Something else to dissect, I guess.

      Looking at all those clamps, I wonder if you've pressurized the intake as a method for weeding out small leaks? I was thinking of a ~15 pound setting on a regulator from a large tank.
      --
      Art Benstein near Baltimore








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    '88 760 Turbo vacuum question... (261,000) and going strong... 700

    posted by  someone claiming to be 760 on  Sat Oct 9 09:45 CST 2004 [RELATED]

    hi frank
    i had the same problem and it turned out to be a faultly vacuum pump motor
    when i hit the gas fan motor would stop and no heat foot of the gas it will work again
    check your vacuum lines as well for leaks
    good luck lindon







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    '88 760 Turbo vacuum question... (261,000) and going strong... 700

    posted by  someguyfromMaryland on  Thu Oct 7 05:48 CST 2004
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    last visit: Thu Feb 8 05:22 CST 2007
    [RELATED]

    This does not sound like an actuator problem to me. It sounds like you can't maintain the vacuum for the system when under boost. This is most likely caused by either a leak in the in-car vacuum system or a failed vacuum check valve in the line from the manifold to the firewall. Look for a white and black valve (ITE makes it). It it's bad, try to find one in a boneyard. Nobody sells them but the dealer and I paid over $20 from Borton. They either work or they don't, so grab several from the boneyard. The by operators never know that the little valve is worth that much.

    HTH,

    someguyfromMaryland








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    '88 760 Turbo vacuum question... (261,000) and going strong... 700

    posted by  dan52 on  Wed Oct 6 17:31 CST 2004
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    Sounds like one of the vacuum actuators that operate the various dampers in the heater distribution box have failed. There are three in all, but the dual acting actuator is the most famous for failue. When the output is decreased, check the airflow out of the defrost vents. In the normal failure mode, the air is directed to these vents.

    The bad news: not an easy fix. It requires quite a bit of disassembly of the dash and beyound to get at it - much like replacing the heater core. Check the FAQs and archives. As I remember, you can remove and plug one of the vacuum hoses and get by. You do loose partial function of this damper, but as I recall, not a catastrophic loss.

    Good Luck,

    Dan






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