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Article by:Kevin Schneider (6/24/2004)
The following is for converting a CRX Si w/B16A & OBD0 ECU to a P28 OBD1 ECU. A lot of the info can be used for other setups as well, so don't be discouraged that my setup doesn't match yours. Why bother converting to OBD1? My reason was so that I could run Uberdata as my Engine Management System. It may seem to cost a lot at first, but keep in mind, even though you need to buy an ECU and distributor, you can still get some money back by selling your old ECU and distributor.

Distributor
You will need to replace your old distributor with an OBD1 version. Make sure you match the engine. For example, if you have a B-series VTEC engine, you'll want a Del Sol, GSR, or Type R distributor. Others may work that I'm not familiar with, but I wasn't going to risk it. If you have a D-series, then get one from a Civic. Just make sure it's OBD1. You have the option of saving some money by buying a used one, however I checked out Distributor King and found out that they had really good prices on brand new Honda distributors. There is more info on their site, but all I will say is that I was very pleased with their service and quality of their product. The price of the GSR distributor that I bought was $195. All Honda-Tech members get a 10% discount, so it ended up being around $175. That isn't too much more than a used one, and in my eyes it's worth avoiding the risk of getting a used one that is about to die (or maybe already dead). Here is what it looked like fresh out of the box:



When you go to install it, you'll notice that it won't plug into your harness. You will have to either put OBD0 plugs on your new distributor, or put OBD1 plugs on your engine harness. I chose the second option, because it will make my distributor easier to replace in the future (or easier to sell for whatever reason). I found a couple of plugs at a junkyard for this purpose. Depending on the conversion harness that you use at the ECU (more on this later), it will affect how you wire your distributor. For my harness, the instructions were to match the wires, color for color. However, the Distributor King distributor had slightly different wire colors in some cases, so I used the following conversion:

Engine Harness OBD1 Distributor PeachWhiteWhite/BlueWhite/BlueBlue/YellowBlue/YellowThin WhitePeachPeach/BluePeach/BlueBlue/GreenBlueFat WhiteYellow/Green
The wires on the two pin connector had the same colors so I did not bother to list them above. Once the wiring is taken care of, simply bolt up the distributor (make sure the shaft is turned the proper way and isn't 180 degrees off) and then plug it into the harness.

Oxygen Sensor
One of the differences between the OBD0 B16A and an OBD1 B-Series motors is the fact that you have to convert from two 1-wire oxygen sensors to one 4-wire oxygen sensor. In order for the ECU to operate correctly, you will need to place the new sensor downstream from the original locations so that it can read all four cylinders. Normally there is additional wiring involved, because you have to add wires for the senor's heater. However, I have a Techedge wideband oxygen sensor that was alread installed in my car, so I will simply be using the narrow band output from that and feed it to the ECU. I will then disable the heater circuit in the ECU when I go to chip my ECU with Uberdata to avoid the Check Engine Light.

Conversion Harness
In order to plug your OBD1 ECU into your existing OBD0 harness, you will need to make some sort of conversion. One option is to hand-wire all of the changes which can be quite tedious. As much as I love wiring, and as much as I like to save money, I opted for a conversion harness that would take care of a lot of work. I was impressed with the quality of it. The harness is reinforced with epoxy where the normally exposed connections would be vulnerable to your passengers feet. It also came with detailed instructions as well.



You will notice that there are several wires that are not hooked up. These wires include those for VTEC, Oxygen Sensor, CEL jumper, etc. I will not go into detail here because the instructions that are provided are very thorough and straight forward.