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Re: Boost Guage Accuracy

This slowness kinda goes against my experience in the 91 200q. My turbo
whines loud enuf to clearly hear.  When I reach max boost of 1.8 bar on the
gauge, the turbo whine stops increasing in pitch. It's not like the turbo
quits spooling up and 2 or 3 seconds later the gauge catches up and reads
1.8.  In 2nd or 3rd gear, it takes less than 3 seconds to go from .5 to 1.8.
The gauge, the turbo whine and the "seat of the pants" all seem to just
about coincide with each other. Did the 91 200q get a faster responding
gauge? When I lift throttle, the gauge drops to .4 or less in well under a

mike miller

-----Original Message-----
From: Scott Mo. <scottmo@teleport.com>

>No, actually it is much simpler than that, the analog signal from the
>pressure transducer gets split and sent off to the boost gauge. An op
>amp is used to buffer the signal. If you remove the ckt. boards from the
>metal frame, you can easily trace out the circuitry because only two
>layer boards are used. The gain of the op amp can be changed to rescale
>the boost gauge readout. This is normally done in the case when you
>change out the stock pressure transducer with the 2.5 bar Motorola
>MPX4250 unit. IC2 on the analog board is the quad op amp used for this.
>There is a uP/controller in the dash assembly (dash computer) that is
>used to convert and display this analog boost signal on the LCD. The
>response of this display is VERY slow. You can change the analog voltage
>input to the display and it takes several seconds before it changes to
>the correct value. This would make for a good project for someone, to
>sort out why it responds so slowly.