FSJ Guy: that code looks good. I have to look at the datasheet for the max232 to see if it's output +12/-12V or TTL serial.

I would just use the circuit in that PDF doc which uses a couple of PNP transistors to interface the two serial lines on the arduino with the one aldl bi-directional serial line.

If you want to read multiple bytes from serial in Arduino you need a loop or you need to call Serial.read() multiple times. Of course, if you need to send some bytes, then get some bytes, and repeat that, then that code can appear in the loop() function. In Arduino land, the microcontroller calls your setup() function once. Then it basically does a loop calling the loop() function like:

while(1) {
loop();
}

I will try and get back here with more info. I've done quite a bit of stuff with Arduino but very little (so far) with GM EFI systems -- that's soon to change as I convert my Grand Wagoneer to EFI as FSJ Guy has done.

One though for those not comfortable with C, you might look into one of the BASIC options like the BASIC Stamp (there are a couple others). But you might as well start with C and with Arduino as it has a MASSIVE following by lots of non-technical as well as technical folks, so there are loads of examples and help to be had.

Michael