I'm hoping some of y'all that have put together a test bench can give me some suggestions here. I've assembled a '7730 with 12v power supply (on my kitchen table) for the purpose of electronic experiment and general torture. Only wires involving +12, ground, and ALDL are hooked up. Running 8d. I'm writing some software for my Mac to interface to the ALDL line, but I'm having a heck of a time with chatter - little bursts of bytes at random intervals, maybe 20-30 bytes every few seconds. I've made sure that all the cases are grounded, exposed power lines are shielded, the serial lines are wrapped, so on, but no love; the chatter is still there, and raising hell with my data reading. Though the software isn't fully functional, I'd bet that half of the "reads" are bad - I don't log them, but *at least* half of them are tossed for bad checksums. Is there something I'm missing? FYI and BTW, I'm a total electronics newby, a total programming newby (at least with OOP, wow it's different), the ECU is from the boneyard, and the power supply was flooded in a basement once. This stuff is interesting, though, so I'd like to pursue it. Suggestions?

TIA
Scott

 

Which BCC are you running in the ECM? Some of them (i.e. '90/'91 vette BCCs) are rather chatty, as other digital components (i.e. the digital dash) are chatting with the ECM (or trying to anyway).

Shutting things up; this is what the mode 8 command is for. :-)

 

I've been using a couple of BCC's: the s_aujp with a romulator, as well as the AXYC on a stock memcal. The noise occurs on both.

Mode 8, huh? Not familiar with that one. ECMGuy talks about Modes 0, 1, 2, 3 and 10. 8's new to me. I've just been sending the Mode 1 (send diagnostic stream). The chatter occurs even before I send the Mode command, though. I'm fairly sure I've got something wrong in hardware - something's not grounded, or there's some RF being picked up from something. Is there some "best practice" method of shielding?

Scott