The turbo bypass valve is not intended to limit boost. It opens when you close the throttle rapidly, in response to the sudden increase in manifold vacuum, to prevent the high-pressure intake air that's now trapped between the compressor and the throttle plate from stalling the turbocharger. The only control for the turbo bypass valve is pneumatic (vacuum line to manifold). The turbo bypass valve should never actuate unless the throttle is closed.

When you say, "the boost gauge does not even indicate full boost", what do you mean by that? I'm assuming you mean it doesn't go all the way to the end of the yellow band, but if you mean something else please clarify. At most, the gauge should only go part way into the red under normal circumstances.

If your boost gauge goes about half-way into the yellow band and stays there when you're accelerating, you're stuck in 'base boost'. This can happen for many reasons. You'll have to search the archives about this if this is your problem, because a) I don't have the gumption to write about it now, and b) there's lots of good info in the archives.

If your boost gauge goes above the middle of the yellow and then jumps back, it sounds like the APC system may be backing off your boost, which IS what it's supposed to do, and it will do it in response to engine knock (there's a knock sensor on the block) or over-boost (sensed by the turbo pressure transducer). If you're running low-octane fuel, or have a lean mixture, the APC system may be doing exactly what it's supposed to. If you have a faulty pressure transducer, the APC system may be limiting your boost early, or the knock sensor may be picking up 'noise' (did you change your plug wires recently?).

Give us some more info (a more detailed description), and we might be able to help you further!

posted by 67.183.219...

• 87 Turbo Keeps Opening Blow Off Valve Under Load - HELP, Adriaan Van, Sun, 16 Oct 2005 15:22:14
  • I had same on my 87 Turbo >, ChipJ, Mon, 17 Oct 2005 05:23:46
    • "It will invariably be the last one you check", Bill S., Mon, 17 Oct 2005 08:11:05
  • Re: 87 Turbo Keeps Opening Blow Off Valve Under Load - HELP, Bill S., Sun, 16 Oct 2005 20:06:43 <-- Viewing This Message
    • Re: 87 Turbo Keeps Opening Blow Off Valve Under Load - HELP, Adriaan Van, Mon, 17 Oct 2005 02:46:14
      • Re: 87 Turbo Keeps Opening Blow Off Valve Under Load - HELP, Bill S., Mon, 17 Oct 2005 05:14:02
  • Re: 87 Turbo Keeps Opening Blow Off Valve Under Load -, nuysdog, Sun, 16 Oct 2005 17:34:03
    • 87 Turbo Keeps Opening Blow Off Valve Under Load -, Adriaan Van, Sun, 16 Oct 2005 19:18:09
  • Re: 87 Turbo Keeps Opening Blow Off Valve Under Load -, Simon S, Sun, 16 Oct 2005 16:25:57
    • Re: 87 Turbo Keeps Opening Blow Off Valve Under Load -, Adriaan Van, Sun, 16 Oct 2005 19:18:34

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