AMC Eagle Test Box v1.0-1.2

I decided it was time to take advantage of the diagnostic connector on my car to help me diagnose issues I might be having. This isn’t a standard OBD2 port like most cars have and there’s no CAN anywhere to be found (except maybe the cup holders). This is a set of connectors that just have 12v signals indicating the status of the many solenoids and switches on the engine. I could go into great detail about what’s available but I don’t have to because I got all my information from here. I’m using the internet archive because it seems the most stable. Thankfully for me, my car is basically a jeep wrangler with a station wagon body on it so jeep resources are a goldmine.

version 1.0

The first revision I used the tachometer I bought to be installed in the dash and built the whole thing in a cardboard box. This simply breaks out all the signals that the page I linked described were on those connectors. There’s an extra thing I’d like to know about though. This car has a lamda o2 sensor meaning that the engine computer tweaks things based on if it’s running too rich or too lean. You don’t get to know HOW rich or HOW lean but you know if it’s not just right. That sensor was not broken out on these connectors. I decided to use a spare pin from my connector kits and crimp a wire so I could populate an empty unused pin on the existing connector with this signal. It was helpfully the grey wire running right under these diagnostic connectors and I tapped it with a vampire tap to spade connector thing. I may go back later and solder/heatshrink it but for now this is pretty good.

New wire

This called for an additional readout on the diagnostic box. I chose an analog 0-1v dc meter, I could have used a digital meter, or a comparator circuit for lean/rich/just right but it’s an analog signal, so it gets an analog movement. There was some concern that loading this signal would screw things up for the computer, the impedance of a galvanometer is just not that much to matter in this case.

version 1.1

The next change I made was to get a real tach that I can permanently build into a metal enclosure when I make one. I have a use for the ford truck tach and its fate is not to be in this test box forever (but I did install the recommended LED for the needle)

version 1.2

In this version I use a cheap amazon tach that’s switchable for 4, 6, or 8 cylinder engines. It also needs to be calibrated so I’m going to tweak it so it matches my snap on digital dwell tachometer. I did have to take it apart though. It came with an awful blue backlit display that I just couldn’t stomach so I replaced the LEDs with green. It’s not as well diffused now but it’s bearable to look at.

The next version (1.3) will be the same enclosure but have a circuit that converts the stepper motor signals into a ‘richer’ or ‘leaner’ indicator. I have a layout (shown above) that should work base on information available online, but I’d like to test it on a running engine before committing to soldering it up. Once that works I can cram this all into a metal enclosure (1.4) and call it done, I have no more add-ons planned beyond that.

Gratuitous video

2 Responses to “AMC Eagle Test Box v1.0-1.2”

  1. My new car! | Evan's Techie-Blog Says:

    […] Diagnostic harness […]

  2. AMC Eagle Test Box v1.4 | Evan's Techie-Blog Says:

    […] entry here, simulator […]

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