GMECM Digest V1 #160

[Peter D. Hipson]

That is what a DRAC is... <g> Some GM vehicles use the DRAC to feed just
the speedometer, and the TCM/ECM is fed from another sender. Other vehicles
feed the output of the DRAC to the speedometer and the TCM/ECM. You need to
know which configuration your unit uses. 

Q: why not use RPM (Engine) to simulate the speed? 

At 10:07 AM 6/23/99 -0500, you wrote:
>Search for drac in the diy_efi archives ...
>
>I did and what I read leads me to believe that the DRAC is a frequency
>converter that is used to drive the speedometer.  Do you have the
>schematic?  If so just do what they did.  Just give the ECM the
>frequency it expects, and be aware that some count pulses and some count
>zero crossings.  YMMV
>
>--steve
>
>Nolan wrote:
>> 
>> 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?
>> 
>> Thanks
>> 
>> Nolan
>
>-- 
>Steve Ravet
>steve.ravet at arm.com
>Advanced Risc Machines, Inc.
>www.arm.com
>
>
Thanks, 
        Peter Hipson (founder, NEHOG)
        1995 White NA Hummer Wagon