I've been researching this for a bit and have yet to purchase or build one but figured I would post it up anyways.

It's called the MPGuino. It basically uses vehicle speed and fuel injectors.

Theres a few things you can do. You can build your own completely and buy all the parts and do a very good amount of soldering (~$40), buy a kit (~$39.51) or a completely built one for (~$63)

Here's some more info, and some more.

Constant 12V+ White Ignition Switch Harness or Use Hot Side of Brake
Switched 12V+ Black/Yellow Ignition Switch Harness
Ground Use Chassis Near Cruise Control Module
Hot Side of Brake n/a Brake Switch
Cold Side of Brake Green/White Brake Switch
Tach Black Diagnostic Connector
VSS Wire Green/Orange ECM behind Glove.22 Pin Connector
Pulses Per Mile 4000 PPM

Hope this helps anyone wanting to go about this!

 

Not sure how many have a VSS? I thought most were cable driven?

 

Sometime in 91/92 they went to a VSS

 

Adam F is right. Sorry should have said that!

 

Why is this OBD1? Why couldnt this work with OBDII?

 

Just a guess, but I would think it has to do with the impedence of the OBD2 injectors being different than the OBD1 injectors. I can't think of any other reason other than OBD2 being touchy about certain things.