If you look around the web, or on this site, you might find a PDF called drac2 with calibration info and pictures and even a pinout. There are scanned documents with fingerprint smudges that show jumper settings for the various "divide by" ratios and images of the two DRAC circuit types. Had I known I'd be uploading those papers to the web in '97, I wouldn't have smudged them back in '93. In '98 or '99 a fellow with some technical writing experience took the original drac.pdf, basically a collection of technician's notes, and re-wrote it as a more presentable paper (drac2). That document also introduced the DIP switch. The included pinout was put together later, maybe in late 99 or 2000 and has a disclaimer as to accuracy. When I researched the pinout I'd often find that a wire or signal had different names in different vehicles but when I'd dig into the service manual the signal itself was consistent. But without a statistically significant sample I wasn't willing to skip the disclaimer. I haven't spoken with too many people who have actually checked these signals. I had two units to test on a bench and both produced signals which matched the pinout. When someone complains to me that they have a unit which doesn't match the pinout it's usually because their service manual calls the signal by another name. It would be awesome if someone either found OE documentation or had enough time and energy to do some component testing so the pinout could be confirmed or removed.
"White box" is a simple identifier but with some dealership background and some years working on these, I know there are speedometer buffers, ratio adapters, signal buffers, digital converters, and plenty of other monikers that have been applied in service literature. Experience has shown that the green box is the green box, and the yellow box is the yellow box, and the orange box is the orange box, and the blue box is the blue box, no matter what make and model it originally came in. Skip all the service manual nomenclature, just go to the junkyard and get the right color box and you're done.
Speedometer cables were standardized at 1000 revolutions per mile. Original speed sensors were two shutter wheels which passed through an IR LED and photo detector with each cable revolution. Much of the programming historically descended from code designed to work with these sensors and you'll find many GM speed signals to be an even multiple of 2000 pulses per mile.
I have a DRAC with a DIP used for confirming correct jumper settings before modifying a customer's part. It's always nice to know you'll get it right before the soldering gun is applied.
Yes, and that's part of the question I asked. There is no way to generate a correct "trans output speed" signal with only a 4k ppm generator. So that signal will not be present in an older manual trans swap, even though the 94-95 S/T/C/K applications with 7427 family pcm and manual trans appear to have used it along with a "vehicle speed signal." Can you think of any specific applications which did not have the "trans output speed" signal but may have used the later 7427 family pcm?Some have TWO outputs for VSS to the PCM (VSS and TRANS OUTPUT SPEED) and some others I've seen only have one output to PCM/ECM for VSS.
Reply With Quote
Bookmarks