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OBD0 to OBD1 Conversion Basics (obd-0 obd-1)

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  • OBD0 to OBD1 Conversion Basics (obd-0 obd-1)

    First let me say that this write-up is not 100% complete, it will not give you EVERY option and EVERY detail. I simply wish to compile most of the info I can find on this subject so that people would have a central article to read up on and be able to learn about the swap before committing to it.

    The easiest way to go about this swap is to purchase a conversion (aka Jumper) harness. This will simplify the wiring a LOT. This harness is basically a set of female OBD0 ecu plugs connected via short pieces of wire to OBD1 male ecu plugs. This then allows you to plug an OBD1 ecu into your car's existing OBD0 main harness. OBD0 to OBD1 conversion Harnesses range in price from around $100 to $170 depending on source and whether its new or used. Here is what one will look like:

    JKConversion Harnesses OBD0 to OBD1 Harness - $150 shipped
    I purchased my Harness Jason (runs the above website) and goes by Blown90Hatch on Both the product and Customer Service/Support was great. There are also a handful of other places out there that sell these harnesses. A good place to find both new and used conversion harnesses is Just do a search, you should find what you need.

    Your conversion harness should come with instructions on how to finish the conversion. But since its good to do some research ahead of time I'll list those things here. So, the following is what you will do to finish your conversion:

    Required Parts:
    -obd0 to obd1 conversion harness
    -obd1 distributor (make sure its one that fits your engine)
    -obd1 ecu (make sure its one that will work with your engine)
    -4 wire heated O2 sensor (preferably one with Honda connectors)
    -obd0 engine harness

    Optional Parts:
    -obd1 injectors and injector clips
    -misc obd1 wiring connectors to help make the conversion be neat and tidy.... as well as oem looking

    STEP 1 - ECU
    -Unplug your stock ecu from your car's main harness
    -plug the jumper harness into your main harness
    -plug your obd1 ecu into the jumper harness

    STEP 2 - Distributor
    -First, I suggest that you diagram the wiring so you don't get confused. Connect your stock obd0 distributor to your obd0 engine harness. Wires on both sides of these 2 connectors should match colors. With one exception - There will be two white wires on one side, and one white wire on the other side. Be careful to note which wire colors these wires connect to.

    -Second, remove the two cream colored plastic distributor plugs from the wires on your obd0 distributor

    -Third, Remove the two gray plastic distributor plugs from the wires on your obd1 distributor

    -Fourth, Take the cream plugs you removed from your obd0 distributor and put them onto the wires on your obd1 distributor carefully matching wire colors. This should be straight forward if you properly diagramed the wires before you removed the plugs since all the colors are the same except for those two white wires (you'll know what I mean when you see it for yourself).

    You have now made it possible for your obd1 distributor to plug directly into your obd0 engine harness. Note that with the above method you will have cream plugs. It is also possible to use the gray obd1 plugs. This would just be reversed. Instead of putting a cream colored connector onto your obd1 distributor you'll take the gray distributor connectors off of an obd1 engine harness and replace the cream plugs that are originally on your obd0 engine harness. Neither is a better way to do it, it just depends on personal preference and what parts you may have laying around.

    STEP 3 - Wiring
    Now, how much wiring you have to run from the engine bay thru the firewall and to the ecu will depend on what swap you're doing. But its all done basically the same way. Different conversion harnesses will have different ways for you to connect the wires at the ecu. Some will have wires that you simply splice into, others may require that you "pin" the wires to the ecu.

    O2 Sensor:
    -Your new O2 sensor will have 4 wires. All 4 of these wires should be ran thru the firewall and to the ecu.
    *Note* It is possible to use a single wire O2 sensor, but it requires some more knowledge (which I haven't looked into yet). But I believe it requires running the 1 wire O2 sensor lead to where the signal wire on the 4 wire sensor pins to the ecu, and then fooling the ecu into thinking the heating element is attached. I think this is done with a resistor, but I'm not sure. Personally however, it seems to me that the 4 wire setup should be the preferred method as this is how the system is supposed to function.

    -There will be one wire for the vtec solenoid which needs to be run to the ecu
    -one wire from the vtec pressure switch will need to run to the ecu
    -the second wire on the vtec pressure switch will simply need to be grounded. An easy ground location for this is the thermostat housing. There should already be a ground junction here.

    Knock Sensor:
    -The knock sensor requires that you run a single wire from this sensor on the back of the block to the ecu

    IAB (for p72 intake manifold):
    -I'm not completely certain of wiring this up. I believe the solenoid requires two wires, a ground and a signal wire. I know the signal wire must go to the ecu, however I'm not sure about the other wire. If you need to wire up the IAB there are resources here and on that should help you get the details. And possibly the instructions for your conversion harness will illustrate this as well

    Other Wiring:
    -Depending on what engine is going into what car there may be extra sensors that you will need to run wires for. There may also be sensors that are in a different place on the new motor. In cases such as these you may need to extent sensor wires or swap connectors in order for these sensors to be plugged in.

    Wiring Tips:
    -I suggest you create a "sub-harness" and loom all of the above wires together. This will create a cleaner and more stock looking install.
    -Use oem connectors whenever possible. If you have access to an obd1 O2 sensor plug it may be useful to use it so your O2 sensor can be easily unplugged from the wiring. Same goes for the vtec solenoid, knock sensor.... etc
    -It can be useful to divide your wiring into two lengths. As you notice all the wiring from the engine to the ecu is in two parts. The engine harness plugs into the main harness. This allows the engine to be pulled without cutting any wires and leaving the engine harness attached to the engine. I suggest finding a oem connector with as many wires as you are running to the ecu. Simply run the wires from all the sensors to this connector, solder to attach the connector. Then solder wires to the other side of the connector and run these wires to the ecu. Now your wiring is divided into two parts. The first will stay with the engine harness should the engine ever need to come out (this also makes it easy to build and integrate this "sub" harness around your engine while the engine is out and simply connect it later). The other portion will remain in the car if the engine is pulled.

    Optional Injector Wiring:
    This is if you decide to run obd1 injectors opposed to obd0 injectors. -cut the obd0 injector clips off of your obd0 engine harness
    -solder obd1 injector clips in place of the obd0 clips
    -unplug the injector resistor box
    -cut the wires leading to this box
    -connect all of these wires to eachother. If possible use the gray plug off of an obd1 engine harness which on obd1 setups does this very thing. If you do not have this plug, then just solder the wires together and heat shrink or tape up the exposted wires.
    Note: You do not HAVE to convert to the different injectors. Both work equally well. Whether you want to swap is based on personal preference, your specific needs, and what parts you have on hand.
    *Note*Obd0 civic and integra and some other prelude injectors are "Peak/Hold" while obd1 and obd2 civic and integra injectors are "Saturated."


    Other Conversion Methods -how to convert to obd1 without a jumper harness

    1) Use Stock Wiring: It is possible to use obd1 wiring from a 92-93 integra and swap it into your 90-91. This means you will need a 92-93 engine harness and a 92-93 main harness. You will basically be removing the stock obd0 wiring and replacing it with the obd1 wiring.
    -This is not a simple swap, using a conversion harness is going to be a LOT easier. The main harness runs from the passenger side headlight, up the fender, thru the firewall, across the firewall (under the dash), back thru the firewall on the driver side, down the fender and to the driver side headlight. This may not sound like much.... but it is. Removing this harness is not easy, and I would imagine installing it would be even harder. Not to mention there are bound to be inconsistencies with wiring, which will mean there will most likely be some cutting/splicing of wires. And this may not be straight forward. But it can be done, and has been done.

    2) Cut / Splice: This method is basically making your own conversion harness. You can cut the ecu plugs off of your main harness and solder on some obd1 ecu plugs. Now an obd1 ecu will plug into your main harness. This obviously is cheaper than a conversion harness, but requires more work, is permanent, and depending on your electrical/wiring know-how has a lot more room for error. If you do the conversion this way you will basically follow the rest of the directions for using a conversion harness, except now you'll pin the wires directly to the ecu. But all the required parts for the conversion harness method are still required for this method.

    *Here is a link to a diagram of which pins correspond to eachother between the two systems. I have not double checked this list personally, so I cannot verify it to be correct or not.

    Also, it is possible to use an obd1 engine harness in conjunction with your obd0 main harness. However this will require modification to the engine harness, main harness or both. In addition to possibly having to run more wires to the ecu. I personally have never done it this way, but I know its possible. It just seems messy and a lot of work. The one car I did see with the wiring done like this looked horrible.....However, I'm sure it can be done neatly if you know what you're doing.

    3) Other, I'm not aware of other methods, but there may be some.... if you know of one let me know and I will add it to this write-up.


    Conclusions and Comments

    1) What is diagramed above is in ADDITION to the rest of the details involved in doing a swap. The above is just the basics to converting to obd1. There will be differences in everyone's specific situation due to the base car, engine, n/a vs turbo, personal preference....etc....etc. Do not forget about these other details.

    2) You may not need to convert to obd1. Just because you are putting an obd1 motor into an obd0 car does not mean you have to convert. There are ways to run the engine off of an obd0 ecu. Which option is better for you will depend on your situation. The Engine Swap Guide in the Teg Tips is a good source for how to swap w/o converting. There is also a lot more info out there, don't be afraid to check out all your options.

    3) I do not know everything about this if you know something I don't, please, enlighten me. I'm here to learn just like everyone else. If there is more info out there I would love to add it to this write-up..... so feel free to contact me.
    Last edited by 91IntegGS; 26 Feb 2004, 02:24:26.
    Track Project DB2 #896
    LeMons Project DA9
    My OG DA9, Wrecked, Stripped, R.I.P

  • #2
    very nice info man.


    • #3
      you are the man thanks a lot dude!


      • #4
        good stuff..very helpful


        • #5
          shit yeah! Nicely done. I think I might make the pin-pin text chart thing into a real chart and host it up. Is that cool?



          • #6
            Great write-up Colin, thanks for the help through my emails as well.


            • #7
              Woah Colin!!!! Thanks a bunch!




              • #8
                Very nice colin... but you for got the obvious, wouldn't it be much easier to buy a obd 1 car? ^_^


                • #9

                  Some of us are masochists


                  • #10
                    Thanks Everyone!

                    Ben, yeah, that'd be great if you wanted to host that. Just let me know if you do and I'll link to it in the write-up.

                    Schu..... yeah, what duy said
                    Track Project DB2 #896
                    LeMons Project DA9
                    My OG DA9, Wrecked, Stripped, R.I.P


                    • #11
                      You guys...


                      • #12
                        Hey man is this the conversion for the engine harness because it doenst look like it. I need the engine harness conversion from obd 0 to obd 1 so if u can write me back and help me out.


                        • #13
                          SilverG2: There is no conversion harness for the engine harness. Shoot me an EMAIL at [email protected] with whatever you're wondering....hopefully I can help answer your question.
                          Track Project DB2 #896
                          LeMons Project DA9
                          My OG DA9, Wrecked, Stripped, R.I.P


                          • #14
                            Did I mention that you rule, Colin?


                            • #15
                              Awesome Colin!! Now it's time to buy the final pieces, jumper harness and 4 wire O2 sensor