DIY-EFI WB datalogging Project

These files are for Educational Purposes ONLY!

I make no claim about their performance/ operation/ origin.
Please don't blame me if you use something here and it doesn't work or breaks something.

Clicking on one of the below links will result in a ZIP file being downloaded to your system. The ZIP file should contain 3 files: A virgin copy of the Base eprom used in this hac, a modified copy of that same image with only the datalogging feature added to the image, and finally a text (.txt) file explaining how to hookup the WB to the ECM in that hac and what the hac is doing..

If you download and use one of my hacs, I'd appreciate you dropping me an email with your email address, in case I need to notify users of any updates or (forbid) any bugs.. My email address is just davis@ this site that you're viewing.

All of these hacs should datalog the WBs AFR directly into the "Commanded AFR" ALDL cell, so that any scan tool/package can read it without modification or post-processing.

I would like to thank the following References/Contributors to this Project:

John <32V_DOHC> from message boards
Dave Zug
Robert Rauscher from gmecm list
Mark Romans
Greg Westphal
Ludis Langens' wonderful ECM info source
Tim Siford

This method should be adaptable to most C3/P4 GM ECMs. If you are interested/willing to test another Mask/BCC, I can provide the assembly code and/or modified bins if you have all the required info on the ECM/Mask/BCC. The main changes between ECMs are:

A/D lookup routine location
2-D lookup table routine location
3 free RAM locations (2 sequential)
1 unused I/O pin on the ECM (0-5V A/D)
About 100 bytes of empty or removable code space in the PROM

So having access to a commented disassembly and ECM schematic is very helpful..

Calibrations (below) were done using a 0v to 4V potentiometer circuit that was monitored by a DMM voltmeter and a scantool on the ALDL.

Diacom(tm) graph of calibration testing

Excel Graph of calibration testing using Craig Moates' software and AKM cable

Here's a short graph of the ALDL RPM and ALDL commanded AFR using my hac during a startup, idle, and drop into gear. This was an actual test using the DIY-WB sensor kit as input to the ECM.


    $8D - AUJP ('92 TPI 350 w/A4)

    $8D - AXXC ('92 TPI 305 w/M5)

    $8D - AFRTuner - WB_hac (de)installer package (Tim Siford's program to add/delete the WB_hac to your existing BIN. Known to work on AUJP)


    $6E - ARAP ('89 TPI 350 w/A4)

    $6E - APYP ('89 TPI 350 {vette} w/M6)