When you refer to the 'max' mark, you mean the end of the yellow band, right? That's not really the max mark, as it's not uncommon for the needle to go somewhat into the red on a normally operating car.

Also, I want to emphasize that there is no 'blow off valve' that limits max boost by bleeding off boost air. Boost is regulated by the APC system, and it only affects the wastegate on the exhaust side; it doesn't act on the intake air side directly. There is a 'turbo bypass valve', but as I explained previously, it's only supposed to operate when the throttle is closed. If yours is opening under boost it is faulty, but I think you'd be jumping to conclusions if you assume the TBV is your problem.

When you see the boost drop unexpectedly, do you also feel a corresponding drop in performance? In other words, if you couldn't see the gauge or hear the 'whoosh' noise (there is one, right?), would you notice anything otherwise? I ask this to determine if you might have an indication (gauge) problem. One time I had a case where the pneumatic line that goes to the gauge had a leak. Boost was there, but it didn't register on the gauge. In my case the leak was in the engine compartment, so I didn't hear anything, but if the leak is in the dash somewhere you might hear the air leaking out.

Otherwise, I'd check all the connections between the turbocharger and the throttle body, particularly the rubber boots (4) that connect all the ducts, for splits or cracks. Also inspect the rubber grommets in the intake manifold, where the various vacuum lines connect, and for that matter you might want to inspect your vacuum lines to the TBV, distributor, charcoal cannister, brake booster, etc. It's possible (though it seems a little unlikely to me) that one of these things is leaking but only when boost is high enough, but not under vacuum or any other time.

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
    • 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 <-- Viewing This Message
  • 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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