GMECM Digest V1 #160 (VSS / DRAC)

[Don.F.Broadus at ucm.com]

The DRAC modules main function is to correct for tire size and gear ratio so
that the speedo reads correctly, I would think if you add the correct pulses
coming out of the DRAC( 2002 pulses per/mile) to the ECM VSS input you will
not need the DRAC. I have been trying to reverse engineer a AGM DRAC it has
7 spots for jumpers 3 are used in the AGM. I think all DRAC modules are the
same except when the jumpers are placed for a specific vehicle tire / gear
ratio then it gets its AGM or what ever designation.
             Please post the 555 circuit when you get it finished.    Thanks
 
Don
> ---
	  

> --Original Message-----
> From:	Jim Sloan [SMTP:leroy at sunflower.com]
> Sent:	Thursday, June 24, 1999 9:55 AM
> To:	gmecm at efi332.eng.ohio-state.edu
> Subject:	RE: GMECM Digest V1 #160 (VSS / DRAC)
> 
> > Hi I'm hoping some one can give me some info.I'm building a pulse
> > generator
> > with a 555 to make aake VSS signal. I order to feed this signal to the
> ECM
> > do I have to go thru the DRAC (its a 7749 Syclone computer) or
> > can I feed it
> > directly to the ECM?
> 
> According the the Syclone Service Manual, " The DRAC processes inputs from
> the VSS and output signal to the speedometer, ECM, and cruise control
> module. The DRAC takes the voltage pulses from the VSS and uses them to
> open
> and close four solid state output switches to ground at a rate
> proprotional
> to vehicle speed."
> 
> This makes it sound like you need the DRAC. Of course, the service manual
> has been wrong before.
> 
> Jim Sloan
> leroy at sunflower.com
> Syclone VIN# 1206
> http://www.sunflower.com/~leroy
> Lawrence, Kansas