SLC Free Wideband Oxygen Sensor Controller Case

thingiverse

This is a custom 3D printed case for the open source and low cost SLC Free Wideband O2 Sensor Controller from 14point7. The controller connects to a wideband oxygen sensor like the Bosch LSU 4.9 or LSU 4.2, giving you the Lambda value (air to fuel ratio) of your exhaust in real time. It has a linear output and a narrowband output that emulates a narrowband O2 sensor. I wasn't satisfied with the metal standoffs included, so I made this case myself. I also wanted to hide the bare PCB when using it, so I added extra pieces for lots of variations. If you soldered the wires directly as recommended or used the white Molex connectors that weren't suggested, use the _wires files. I used C-Grid III (locking shrouded) connectors instead, which surround the pin and make contact on multiple sides, rather than the single sided connection from the white Molex connectors. The specific parts I used are 90136-2205 and 90136-2206 (connectors), 90156-0145 and 90156-0146 (housings), and 90119-0109 (crimp pins). Since they're shrouded, I had to install them on opposite sides of the board for them to fit. I also had to snap off the outer tabs on the rear of the connectors for extra clearance around the mounting holes. I installed connectors for the programming header and additional I/O too. If you want the programming header accessible, use the _prog files, and if you want access to the I/O pins, use the _io files. Note that there are several variants of SLC Free - A is open source, B and C are closed source. Variant A only has a bar graph, and only works with LSU 4.9 sensor, while B and C show the values in text, and work with both LSU 4.9 and LSU 4.2 sensors. I included case parts for all three types - _a has labels to interpret the bar graph, _bc just has lambda and temperature labeled. I'm currently running variant B, but have a spare chip and programmer, which I plan to use to load variant A (and possibly customize the firmware if needed). The Sketchup model for all these pieces is included as well. Post-Printing Assembly Once you have the desired top, middle, and bottom pieces printed, place the SLC main board into the middle piece, then flip it over and press the LCD into the socket. It won't go all the way in because the middle piece is also used as a standoff to keep the LCD board from touching the top of the capacitors on the main board. Then put the printed top and bottom on the assembly and attach with #4-40 screws. The top screws should be approximately 5/8" long, while the tall bottom piece (_cgridiii) should use 5/8", and the short bottom piece (_wires) should use 1/2". Custom Section What's it used for? I used this to debug a problem on my truck that was causing me to fail my emissions test. I had a high NOx value, and very low HC and CO values. These values told me that I was likely running very lean (too much air, not enough fuel), so rather than making a change and paying for another test (and probably failing), I swapped the OEM narrowband O2 sensor with a LSU 4.9 wideband sensor. I connected it to the SLC Free, and connected the narrowband output to the connector that OEM sensor was plugged into (since the truck ECU needs an O2 sensor signal). This let me make changes (cleaning fuel injectors, fix vacuum leaks), test drive it, and see my AFR in real-time while driving. After making some changes, I got it where the burn was nearly stoichiometric (Lambda=1, approximately 14.7:1 AFR) during normal driving, so I put in a new narrowband O2 sensor (the old one was destroyed while removing it), took it to the emissions test station, and PASSED! :-) I also plan to use it to tune my motorcycle. By putting the O2 sensor in a tailpipe clamp in the muffler, I can tweak the fuel tables for optimal performance. This only works for vehicles without a catalytic converter, like many motorcycles (otherwise, you need to put the O2 sensor before the cat to get an accurate reading).