Wire a JDM B20A with a PK2 ECU

The question I have been asked it: Why a use PK2 ECU and not the JDM PH3 ECU that was made for this specific engine? Well, the answer is simple. The PH3 ECU is very hard to come by. The Engine importers rarely get to import them because there is so little demand. I could not find a PH3 ECU at the time of the swap so I just thought I'd use what's closest and the PK2 was the right choice. How lets start with the conversion.

I have developped a special chip that will basicaly turn any PK2 ECU to PH3 specs. If you don't find any PH3, it's no problem, just chip your PK2 and you're done. Contact me if you need your PK2 chipped. Now, let's get back to the conversion.

The Conversion:

Like most JDM engines, my B20A came with a cut wire harness. Seems it was way too hard to disconnect the plugs for them...

I first thought I would install USDM plugs on my JDM harness but it turned out to be more difficult than I thought. Some of the wire colors are different between the JDM and USDM harness for the same sensor. For example, the EGR sensor has 1 wire that was red instead of yellow like on the JDM engine.

So, instead of installing plugs on my JDM wire harness, I decided to modify a USDM A20A harness.

The major difference between the 2 harness are the distributor plugs and O2 sensors.

Distributor:

The A20A has a TDC sensor (Orange and White wires) and a Cyl Sensor (Orange-Blue and White-Blue wires) located directly on the distributor connector. This means it has only 1 plug (the plug on the right)

The B20A is a bit different.

It has a Crank sensor (Blue-green and Blue-Yellow wires) and a Cyl sensor (Orange-Blue and White-Blue wires) located on the distributor. It has the TDC sensor (Orange and White wires) located on the exhaust camshaft.

It has 2 plugs. The TDC sensor plug is on the top of the picture while the distributor plug (Crank/Cyl) is on the bottom

If you want to modify the A20A harness, just remove the old distributor plug and swap it with the ones from the B20A. I suggest you also change the temp sensor plugs because they are tied with the distributor plugs. Their length is also different since the sensors are located at a different place on the DOHC engine. You do not HAVE to replace them but it would look more OEM :)

Once you swapped the plugs, just splice the TCD/CYL sensor wires with your existing wires.

In order to remove the plugs/wires, you need to remove the tape from the wiring harness. The tape was old and would easily brake on mine so I replaced everything.

The wiring harness should look like that....a complete mess:

You are then left with 2 extra Crank Sensor wires to add to your A20A main harness plug(the Blue-Green and Blue-Yellow). Notice that those wires are shielded and you should use shielded wires. I personally took the wires from the B20A harness. I noticed that there were 2 unused holes in the A20A Engine connector so these can be used to add the crank sensor. (lucky me)

Remove the 2 rubber plugs that block these holes and the connector should look like that.

You can use the pins from a sensor on the B20A harness and put them in. I used the pins from the service connector (blue and black wires), connect them to the crank sensor wires and you're set.

That's it for the distributor plugs.

O2 sensors:

The B20A has only 1 O2 sensor while the 88-89 Accords use 2 (like the B20A5 Prelude). The 86-87 Accords have only one sensor also. However, if you want to use a B20A5 ECU (explained next) you will need to modify the harness (like I did). I didn't want to use only 1 O2 sensor and end to be stuck with a check engine code and modify my harness again... so I decided to use a modern O2 sensor with a heater.

I basicaly used the O2 sensor 4 wire conversion described on Tome Coleman's website.

Like Tom said. You connect the 2 wires from the A20A O2 sensor input to the White wire on the 4 connector sensor. The green wire goes to a ground. I used the big Black-Red wire that's already in the A20A harness as a ground.

Now you can connect the O2 sensor heater. (the 2 black wires). I used the Black-Yellow wire near the alternator as a switched power. The other wire was grounded to the Black-red wire like the green wire.

Since the O2 sensor goes at the back of the engine on the downpipe, I located the O2 plug near the alternator plug.. That plug can come from any Honda. In that case it came from a 92+ civic.

Now, make sure all connections are tight and solid then re-tape everything...

It should look like that

All you need to do is add the wires to the ECU.

ECU Wires

If you do not have the PH3 ECU for your B20A (Like me), you can use a PK2 ECU from a 88-91 USDM 2.0SI Lude. This ECU was meant to be used with a B20A5 which is almost identical to the Accord JDM B20A.

I will explain the wiring procedure for the PK2. However, the PH3 should be similar.

First of all, you will need to route the 2 crank sensors from the enginebay to the ECU. Choose whatever method you want as along as you're using shielded wires. It's important to use shielded wires in order to prevent any interferences.

I personally chose to route the wires side to side with the OEM A20A harness in the left side fender. Those are the ONLY wires you will need to add to the A20A chassis harness so take your time and attach it firmly so it will not hang everywhere and look like crap. Those wires need to be routed under the passenger seat. I took a 10 feet long wire so I knew I had long enough if I made mistakes or encountered routing problems.

Now, please take a look at the 2 ECU pinouts.

• 88-89 Accord PJ0 ECU
• 88-89 Prelude PK2 ECU

You will need to add wires and swap some pins in order to make it work. It's not a hard job to do beleive me. I suggest that you go to the junkyard and buy the connectors our of a B20A5 Prelude. It will make things easier when adding the missing pins on the PJ0 harness. While you're at it, grab the igniter and timing connector (on the right side in the enginebay). You will need the those later in the swap.

Here is what needs to be worked out:

• Bypass control Solenoid (IAB)
• Fuel Pump Relay
• Igniter
• Ignition Timing Input
• Crank Sensor
• Speed Sensor
• P/S Pressure Switch

ECU PINS

The OBD-0 (or pre OBD) ECU have their pins labelled like this.

There are 3 connectors:
The big white/beige connector with 18 pins is called connector "A". It is the connector that's at the left of the ECU

The black connector with 20 pins is called connector "B" and is located in the middle.

The smaller black connector with 16 pins is connector "C" and is located on the right.

Now that you know your A-B-C, here's how the pins are labelled when you look inside ECU the with the wires unplugged. Refer to the ECU pinout to match the wire colors ans see if you read the pins properly.

Now that you know how the pins work, you will need to remove the OBD-0 pins from the B20A5 ECU harness you grabbed at the junkyard (you got one right?). To remove the pins, you might need a small electronic flat screwdriver. I assume that you know how to remove pins. It's not too hard but can be a pain if you do not use the right tools.

Now let's begin with the Pin conversion.

• Take the wire at pin A8 (White) and remove it. This wire is used for the Vacuum advance solenoid. The PK2 doesn't have such a thing so it's not needed. However keep it close to the ECU, we'll be reusing this wire for the igniter.
• Take the wire at pin A14 (Red Green) on the Accord harness (IAB VALVE) and put it at pin A8. This is where the PK2 ECU has it's IAB wire.
• Take the wire at pin A6 (Green Black) on the Accord harness and put it at pin A14 (where you took off the IAB wire).

• Take the wire at pin B5 (brown) in the PK2 harness and add it in the same place in the Accord Harness. This wire has to be connected to the Ignition timing connector. The other pin of the Connector needs to be spliced at pin C12.
• Take off the wire at pin B10 on the PK2 ECU (blue-green) and add it to the PJ0 harness at the same location. Connect that wire to the shielded wire you added for the crank sensor (make sure to match the colors with those in the enginebay)
• Take off the wire at pin B12 on the PK2 ECU (blue-yellow) and add it to the Accord harness at the same location. Connect that wire to the shielded wire you added for the crank sensor (make sure to match the colors with those in the enginebay)
• Take off the wires at pin B15 and B17 on the PK2 harness. Add them to the Accord harness at the same location. Connect those 2 wires to the white wire you removed at pin A8. This wire will be used to activate the igniter.
• Remove the wire at pin B18 on the Accord harness (Yellow) and swap it to pin B16. This is wire is used for the VSS and the PK2 needs it at pin B16.
• Remove the wire at pin B9 on the Accord harness (Green) and swap it to pin B18 where you took the VSS off. It seems that I do not have a Power steering pressure switch on my car... it doesn't affect the ECU at all. That wire was red on my Accord harness.

Nothing needs to be done to connector "C" except the Ignition Timing plug ground that needs to be connected at C12

Igniter

Now let's get to the Igniter Wiring. This is an easy part beleive me.

Refer to the following Igniter Wiring
Prelude Pk2 Ignition Wiring

There are 5 wires going to the igniter.

• 2 white wires (which are spliced together)
• 1 Black wire
• 1 Blue Wire
• 1 Black-Yellow wire.

The wiring is pretty straightforward.

• Take the plug going to the Ignition coil from the A20A distributor and cut it, leaving enough wire look to work easily. This is the 2 wire connector with a separate black wire for the radio condenser.
• Splice the coil wires to their corresponding colors on the igniter (Blue, Black-Yellow and black)
• Connect the black wire to a known good ground (there is a ground to the left of the vacuum box)
• Take off the white wire going into the vacuum box for the cold advance solenoid. You could just cut it but I prefered to just take it out of the connector. Connect this wire to the white wires of the Prelude Igniter.
• Mount the igniter somewhere!
• You're done!

Voila! Your B20A Wiring is complete
If anything needs to be clearer, feel free to ask for some explanations!