I've got a project I need to get started on now that my car is running thanks to the help provided here in a previous thread! I have a 92 Cutlass with an L67 swapped in. I also have a gauge cluster from an earlier model Cutlass International, which takes the ALDL input from the PCM to determine the RPM. But now that I've swpped over to OBDII L67, I don't have ALDL and therefore I don't have a working tachometer! So what I want to do is take a tachometer signal (presumably from the ICM?) and with either a Raspberry Pi or Arduino, simulate a fake ALDL stream containing only the RPM signal so that the cluster reads it and displays engine RPM. All the research I've done I have only found people who made ALDL stream *readers* out of Arduino's and Pi's, but I need information on the protocol to simulate *writing* an ALDL stream. The rest of the project I think I can handle myself, I just need the assistance of someone familiar with the ALDL protocol to walk me through that! Anybody interested in helping?