In this edition of our tech posts we will show you how to properly wire and setup a nitrous or water/methanol injection system to be used on your OBD1 Honda/Acura ECU setup using either Hondata S300 or Neptune RTP.  The same wiring, principles and setup can apply to other ECUs like KPRO, KTUNER and others….but we are only specifically covering the OBD1 Honda ECU like a P28, P06, P72, P05, P61, P75, etc….



Since a Nitrous and Water/Methanol system are injecting something into the air stream entering the engine, we can treat them roughly the same.  However, you must remember the purpose and what you are doing with each of these.  With nitrous, we are adding extra OXYGEN into the stream, so we will generally remove some ignition timing and add fuel to account for the additional oxygen entering our engine.  With water/meth we are adding cooling (h20) and octane boosting (meth) to the intake air which means we will tend to remove fuel and add timing accordingly.  These are just general guidelines to follow…please make sure you do your own proper amount of research on the subject and educate yourself so you can tune this properly or at least explain to your tuner intelligently how you have setup the system to aid them.
Hondata software has very detailed HELP files; I suggest you use these to your advantage along with their instructions.  See the following link to the Hondata Help - Nitrous Setup:
This help file goes through the FUNCTION, INPUT, OUTPUT and CONDITIONS, just the same as we have gone through on the video above along with the wiring diagram for the nitrous output and relay.

Keep in mind on the arming switch it will depend on which INPUT you use whether to supply a ground to the switch or a 12 volt.  In the diagram they have used B8 (Power Steering switch) or B5 (A/C Switch), which are both ground inputs…while in the video I have used the D2 (Brake Switch) which is a 12 volt input.  There are OPTIONS here, and no one way is right or wrong.
It is important to hook up the RELAY exactly as shown.  All automotive relays will have these number markings to allow you to connect everything correctly.  It is important here to use the proper GAUGE wiring for the current that will be drawn by the solenoid.  Our relay kits we offer will provide you with the proper sized (overkill really) wiring and a few crimp or connector options for hooking up not only fuel pumps but also nitrous relays (fuel or nitrous) and water/methanol systems as well.
If you have any questions after watching our video and reading this article, please contact your tuner for further help.  If you have any questions about the products we offer, please email
For more information:         Hondata Engine Management           Neptune Engine Management             KTuner Engine Management