I have a question about DRAC modules. I have done a search, but haven't managed to find exactly the info i am after.

I have recently converted my car to run a 16168625 PCM, running $E6. This PCM has 2 speed inputs. One is "Vehicle Speed Signal" at terminal F13, I have mananged to get this working perfectly.
The other is called "Trans Output speed" at terminal F12, this is the one I am having trouble with. The schematic from the 93-95 truck that the PCM came from shows that the 40pulse/rev speed sensor signal (AC sine wave?) goes to the DRAC module and this box generates the 2 signals mentioned above.

My understanding of the DRAC is that it converts the 40pulse/rev AC sine wave signal to a much lower frequency DC square wave for the "Vehicle Speed Signal", but what type of signal does it produce for the "Trans Output Speed" PCM input?

TIA,
Ben.

 

<long whistle>
40 pulses per mile?

As I recall, from having read about such matters on the internet, the DRAC took a *high rate* A/C signal and then output a 2,000 PPM, for the ecm, and then a 4,000 PPM for the cruise. May be all wrong, thou, nothing I have has one.

 

On my vehicle with the 16197427 PCM which is very similar to the 16168625 PCM, pin C13 on the DRAC module is connected to F12 on the PCM and is a mirror signal (AC sine wave) of the 40 pulse per rev VSS signal. I have verified this with an oscilloscope as I used this signal to interface my LM-1 WBO2 for MPH. The PCM uses this signal along with the RPM/VSS ratio constant to figure tranny speed. The 2000 pulse per mile signal (square wave) from pin C11 of the DRAC goes to F13 of the PCM and is used as a vehicle speed input independant of the tranny input. I believe that you can actually do without the tranny speed input and only use the vehicle speed input as long as the "Output spd fm Dig Ratio Adaptor" bit is set (bit 4 at L5D02 in the $0D mask) although I have not verified this. Check out this file ftp://ftp.diy-efi.org/uploads/DRAC2.pdf. It may help. HTH

 

sorry!! typo.. 40 pulses/revolution!!!
;-)

Thats HaulnA$$, very helpful.

 

If you haven't seen it, this helps answer most questions about the DRAC.

DRAC2

 

I think i have found the equivalent bit in the $E6 hac.
It is "Output Speed from DRAC" at 5A02, bit4.
I have run the car up on stands with this bit not set (stock) and set, but it seems to make no difference.. What difference would you expect?
My problem is that I cannot get the tcc to lock There are a couple of bits tin the $E6 that allow you to tell it that there is not a 4L60e, but a 700r4 in the car, but it still seems to be looking for more feedback from the trans, and continues to generate DTC's that are not relevant to a 700r4.... If only it was easy to generate a sine wave from the VSS pulses.... I have applied a sine wave to the input in question ,and it does show the correct 'trans output speed' in datamaster....

 

I went all through this with my 4l60e installation and I had to use a DRAC module also. I put the scope on all the DRAC outputs and pin 13 is a 40 pulse per revolution square wave. It doesnt actually output anything but goes from ground to open 40 times per revolution of the tranny output shaft. I think that's what HaulnA$$ was saying also.

Steve

 

Maybe there's something in that mask that requires the 4th gear switch to be on to enable lockup.

 

Sent ya, an email

 

I don't think so.. There's no 4th gear switch input to the PCM...

 

I just happened to run across this discussion while poking around the boards and remembered seeing a sticky in the S-Series.org 4.3L Tech forum dealing with the DRAC and re-calibrating it for tire size or rear differential changes.

The topic is here:
http://forums.s-series.org/viewtopic.php?t=25875

Original author's page is here:
http://614streets.com/drac.html - Contains a table of GM production DRACs and their values as well. Going off the pin settings on this table would get you close to the correct DRAC setting, but to be more precise, use:

The DRAC Calculator:
http://www.philter.com:81/cgi-bin/drac.pl


Don't know if that'll prove useful or not, but now you know!
I figured maybe you could recalibrate your DRAC to match the rear differential and tire size for your car and then use the DRAC to solve your problem.

 

Thanks for those sites! I actually stumbled across them a few days ago myself ;-)

When I substitute the 700r4 for a 4l60e I will use a DRAC. At the moment, my goal is to get the 'trans output speed' to work with the 700............

 

Oh, OK.

 

Heh.. that's my site. the :81 at the end of the link provided above is temporary. If you want to bookmark the page or post it anywhere else, leave that out so it won't break in the near future when I relocate the server to it's normal port.

Teeleton