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 Honda VTEC or non-VTEC D, B, F or H series engine, and its advanced boost control capabilities make it one of the most versatile Honda tuning systems. The only downside to the Hondata S300 is the level of installation difficulty. The S300 is more complicated than the common “piggyback” tuning system, as it is installed inside the ECU where a typical performance chip would be installed. Another drawback of the system is that when you buy the S300 you are only buying the Hondata unit and the software. It is up to you to make arrangements to install it. However, with this step-by-step tutorial, you can now successfully install your Hondata S300 on your OBD1 ECU yourself!

The first step to a successful installation is making sure you have everything you need. This is a somewhat complicated process, but with the right equipment and parts it should go smoothly. The Hondata S300 (part number S300) is designed for US Market (USDM) Rectangle or “Big Box” OBD1 Civic / Integra style ECUs. Hondata part number S300J is designed for JDM Square Case Civic / Integra OBD1 Style ECUs (Japanese Market). 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. Honda ECUs accepted for use with the S300 are: P06, PR4, P28, P30, P61, P72, and P75. Any non-vtec ECU is supposed to only be used in non-vtec applications. If you are using 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 caps from your ECU and set both caps 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 that it holds inside the ECU case and set them aside. Turn your computer over and remove all the screws holding the circuit board to the ECU case and notice how they are slightly different from the screws on the ECU covers. The ECU board will now be able to be removed through the bottom of the ECU housing. Be especially 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 has been removed, we can get to the fun part. Using a desoldering tool or desoldering braid, desolder 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 further away from the full ECU connectors 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 labeled 27C256, just skip this step. Clean all areas of the ECU that you unsoldered with flux to ensure no loose solder is left on the board or in the way of the desoldered holes. To enable the data logging capabilities of the Hondata S300, cut off one leg of the resistor at the location labeled j12. For a cleaner look, you can completely de-solder and remove the resistor if desired.

Now let’s move on to the installation. The best way to ensure a complete solder at the joints is to apply a thin coat of flux to the back of the desoldered joints before continuing with the next steps. Begin by installing the two rows of 14 dowel strips in the now empty holes that accompany 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 protrude through the unsoldered holes. Next, install the 24-pin chip provided with your S300 in the space labeled 74hc373. Make sure the crescent shaped notch on the chip faces 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 in it further from the ECU sockets from the previous step. If your ECU has a gap labeled R54, solder the resistor provided instead. Polarity doesn’t matter. It can be installed in any direction. Next, press the Hondata S300 circuit board firmly 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 into the ECU case. Mark the area on the ECU housing that blocks the S300 USB connector. Carefully remove the ECU board from the case once more and, using a grinder or hacksaw, cut out the marked area to allow your 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 remaining solder residue or flux. Reinstall the ECU board into the case taking care not to damage any components. Install the screws that hold the circuit board in place, the small screw, and the metal clip on the side of the plugs, and the upper and lower ECU covers. Make sure to carefully stick your fancy new Hondata sticker on your ECU for it to work properly.