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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.
__________________ Red/Red 84 Vette. 383 Crossfire 12.26 at 114mph
Originally posted by ben73 My understanding of the DRAC is that it converts the 40pulse/mile 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?
<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.
Originally posted by ben73 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/mile 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.
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
__________________ If it doesn't make it go fast, stop fast, or look cool, its fluff!
Originally posted by Grumpy <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.
Originally posted by HaulnA$$ I believe that you can actually do without the tranny speed input and only use the vehicle speed input as long as the "Output spd fm Dig Ratio Adaptor" bit is set (bit 4 at L5D02 in the $0D mask) although I have not verified this.
I think i have found the equivalent bit in the $E6 hac.
It is "Output Speed from DRAC" at 5A02, bit4.
I have run the car up on stands with this bit not set (stock) and set, but it seems to make no difference.. What difference would you expect?
My problem is that I cannot get the tcc to lock There are a couple of bits tin the $E6 that allow you to tell it that there is not a 4L60e, but a 700r4 in the car, but it still seems to be looking for more feedback from the trans, and continues to generate DTC's that are not relevant to a 700r4.... If only it was easy to generate a sine wave from the VSS pulses.... I have applied a sine wave to the input in question ,and it does show the correct 'trans output speed' in datamaster....
I went all through this with my 4l60e installation and I had to use a DRAC module also. I put the scope on all the DRAC outputs and pin 13 is a 40 pulse per revolution square wave. It doesnt actually output anything but goes from ground to open 40 times per revolution of the tranny output shaft. I think that's what HaulnA$$ was saying also.
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.
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:
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.
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.
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.
