Help! Need rpm activated switch w/ hysteresis!!

[Bruce Plecan]

-----Original Message-----
From: Jason <srgnt03 at earthlink.net>
To: diy_efi at esl.eng.ohio-state.edu <diy_efi at esl.eng.ohio-state.edu>
Date: Wednesday, March 10, 1999 1:57 AM
Subject: Help! Need rpm activated switch w/ hysteresis!!

Use two rpm switches.  The on turns on a SCR, off interupts power to SCR.
Bruce


>I need some help here, and soon. I have a variable geometry manifold
>(Schrick VGi) that uses vacuum to open up an interior flap that changes
>the runner geometry and thus the torque curve. It uses a controller,
>two-way vacuum switch, and a vacuum tank. 
>
>The controller has a ground, switched 12V+, an rpm signal tap from the
>factory Bosch ECU, and a two pin connector that it uses to activate the
>two-way vacuum switch (that's connected to a little diaphram that opens
>the flap in the manifold). The controller has an adjustable rpm set
>point for the rpm opening point (adjustable from 2K-6.3K rpm), and it
>has an adjustable hysteresis setting from 0-200 rpm. The best torque is
>made when the settings are 4K for the flap to open (short runners, high
>hp up top), and a 50 rpm hysteresis (so it closes at 3950 rpm). Works
>VERY well when all is functional. Rpm set points are made by DIP
>switches (8 of them). Test mode will cycle the switch on/off (set all
>DIP switches ot OFF), and turn the LED from green(closed flap) to red
>(open flap, and back...
>
>The controller is done for. It will not even function in test mode. A
>new one is $300. That's insane, for such a simple PCB. I tested ALL my
>connections for continuity, and all check out. The wiring is sound, and
>everything checks out. The controller will activate the two-way vacuum
>switch as soon as it gets switched power. Regardless of rpm signal, or
>set point. I looked at the PCB (encased in epoxy, except for the DIP
>switches)and there appears to be a little discoloration or corrosion in
>there. I'm an ME, not an EE...so I need a replacement controller.
>
>I looked at my Summit Racing catalog (pg. 119 & 126)and found a couple
>rpm switches...but I don't think any of them have a hysteresis function.
>The MSD one has a "low" and a "high", but that's it. I need something
>that offers me adjustability from 3500-4500 rpm, with about a 50-100 rpm
>hysteresis. I don't want to fab a PCB, I don't want to spend over $100,
>and I need something soon. Without a controller, I have to choose
>between low end torque, or high end power (by having the flap closed, or
>open all the time). Drive-ability is less than perfect.
>
>So, does anybody know of an rpm switch that has an adjustable "on", but
>also has a hysteresis setting too? Maybe I could get the MSD unit, and
>set the "off" rpm set point lower than the "on" set point (an have a
>negative overlap, making my own hysteresis)???? Thoughts?
>
>Jason
>'93 VW Corrado VR6 w/ failing Schrick VGi controller!!
>