The Hondata S300 is one of the most advanced Honda OBD1 tuning systems available on the market. The S300 has the ability to operate any VTEC or non-VTEC Honda D, B, F, or H-series engine, and its advanced boost control capabilities make it one of the most versatile Honda tuning systems around. The only drawback of the Hondata S300 is the level of difficulty to install it. The S300 is more complicated than the common “piggy-back” tuning system, as it is installed inside the ECU where a typical performance chip would be installed. Another drawback to the system is that when you buy the S300 you are buying just the Hondata unit and software. It is up to you to make the necessary arrangements to install it. However, with this step-by-step tutorial, you can now successfully install your Hondata S300 OBD1 ECU yourself!
The first step to a successful installation is to make sure you have everything you need. This is a somewhat involved process, but with the right equipment and parts it should work without a problem. The Hondata S300 (part number S300) is designed for the US Market Rectangle (USDM) or ‘Big Case’ OBD1 Civic/Integra style ECUs. Hondata part number S300J is designed for Civic/Integra style ECUs with JDM (Japanese Market) square case. These are not interchangeable so make sure you have the correct S300 unit for the ECU you are using. This installation guide applies to the USDM variant only. Accepted Honda ECUs for use with the S300 are: P06, PR4, P28, P30, P61, P72 and P75. Any non-vtec ECUs are only supposed to be used in non-vtec applications. If you are going to use a P06, Pr4 or P75 ECU, you must also perform a non-vtec to vtec ECU conversion with the Hondata S300 installation to properly operate a VTEC engine.
Let us begin. Unscrew the top and bottom covers from your ECU and set both covers aside. On the side of the ECU where the wire harness plugs are, you will see a small Phillips head screw. Completely remove this screw and the small metal retainer it holds to the inside of the ECU housing and set them aside. Flip your computer over and remove all the screws holding the circuit board to the ECU case and notice how these are slightly different than the screws for the ECU covers. The ECU board can now be removed through the bottom of the ECU housing. Be very careful not to damage the ECU board or its connectors if the board needs a little more coaxing to break free from the case.
Now that the board is removed, we can start with the fun part. Using a de-soldering tool or de-soldering mesh, de-solder the 28 solder joints marked 27c256, the 24 joints marked 74hc373, and the four holes in the space labeled CN2. You will notice that the CN2 section on the board has 5 holes. You can leave the solder joint furthest from the ECU connectors full as it will not be used. On most boards there will be two solder joints labeled R54. These will also require desoldering. If your ECU does not have the area labeled R54 directly above the 28-hole area marked 27C256, simply ignore this step. Clean all areas of the ECU that you desoldered with flux to ensure no loose solder remains on the board or in the path of the desoldered holes. To enable the data logging capabilities of the Hondata S300, cut a lead off the resistor at the location labeled j12. For a cleaner look you can fully desolder and remove the resistor if you wish.
Now we go to the installation. The best way to ensure complete soldering at the joints is to apply a thin layer of flux to the back of the desoldered joints before proceeding with the following steps. Begin by installing the two rows of 14-pin strips into the now vacant holes next to the area labeled 27c256. Make sure the pins are facing up on the ECU board and that you solder them to the back of the board where they stick out through the desoldered holes. Next, install the 24-pin chip that came with your S300 in the space labeled 74hc373. Make sure the half moon notch in the chip is facing the ECU sockets and then solder in place. Insert the 4-pin strip into the open holes labeled CN2 and solder in place. There should be a hole left in CN2 with nothing further away from the ECU plugs from the previous step. If your ECU has a space labeled R54, solder the provided resistor in its place. The polarity doesn’t matter. It can be installed in any direction. Then firmly press the Hondata S300 circuit board into place on the two rows of 14 pins on 27c256 and four pins on CN2. Be very careful not to bend or break any pins. Once the Hondata S300 board is in place, carefully slide the ECU board back into the ECU cage. Mark the area on the ECU housing that blocks the S300 USB connector. Carefully remove the ECU board from the housing once more and, using a grinder or hacksaw, cut out the marked area to allow the USB cable to connect to the S300’s USB port.
Thoroughly clean the ECU housing and circuit board with a quality electrical parts cleaner to remove any residue or remaining solder flux. Reinstall the ECU board into the housing being careful not to damage any components. Install the screws that hold the circuit board in place, the small screw and metal clip on the side of the plugs, and the top and bottom ECU covers. Be sure to carefully stick your fancy new Hondata sticker onto your ECU in order for it to work properly.
