Some people collect stamps, some people like to tinker
with embedded controllers. I am one of the second kind
of people. It's much more rewarding and if you spill a
glass of soda, your friends won't find you dangling
from the bathroom ceiling.
In the process of owning my first Fiero I bought the GM factory service manual. They mentioned the "proprietary" ALDL connector with a mysterious "data output". But I'd need to buy some $300+ scantool to access that data! Ha!, I thought, since I had stopped living in a bamboo hut months ago, I thought I could break that code. Armed only with my oscilloscope, pencil and paper, and of course my wit, I started working on decoding that protocol.
Since I was a student at that time I had loads of free time and finally found out what most of those bits meant, for my V6 anyway. I later found out that the protocol is similar for the 84-86 L4, although not the same. The 87/88 L4 Fieros use a completely different protocol. Thus, all scantools featured on these pages work with the V6, and I'm working on making them compatible with the 84-86 L4, although this is a work in progress. Most of them don't and won't work with the 87/88 L4 though!