D16Z6 installation and OBD0 (88-91) to OBD1 (92-95) wiring conversion

By Kurt_W

This conversion to an 89 CRX Si.

List of the parts used/modified:

1. One slightly used 89 CRX Si
2. 93 D16Z6 (further known as Z6) 1.6L SOHC VTEC
3. Partial engine harness from the 93 D16Z6 and harness parts from a 92 Civic DX auto
4. 95 Civic EX P28 ECU (manual)
5. 92 Civic Si distributor
6. #4107 fuel injectors years unknown (will remark more on this later)

Remarks on installing the D16Z6 itself

Installing a Z6 itself is pretty close to dropping a D16A6 (a.k.a.A6) engine in. Alterations that need to be made include:

1. Replacement of the Z6 driver side engine mount with the one from the A6. The A6 mount has an “extra” piece  that wraps around from the front of the engine, it is shaped like an “L”. This “L” piece is not needed and for that matter, doesn’t quite fit on the Z6 (wrong angle). In order to get the timing belt covers to fit over the A6 mount, some cutting of the bottom cover is required.

2. The crankshaft pulley that should be used on the Z6 is the one for the Z6. The reason for this is that pulley is balanced for the Z6. The A6 pulley will fit but there is the potential for premature crankshaft bearing wear due to it not being balanced for the Z6. The belts on the Z6 pulley are of a different groove number then the AC and alternator belts off the A6, but it doesn’t seem to matter so long as the belts are tensioned properly. As for accessory over/under turning, no problems have been experienced in the almost 10000 miles put on the car since the swap.

3. Both the intake and exhaust manifolds used were from the Z6.

The intake is ported specifically for the engine therefore logically it is best that it is used for the engine (as opposed to the A6 intake manifold). Slight modifications had to be made to the engine harness by transplanting some of the plugs off the 93 engine harness onto the 89 harness so that the intake sensors could be plugged in. Since the MAP sensor on the Z6 (93-95) is on top of the throttle body, it is necessary to extend the wires for the MAP sensor plug from the 88-91 location on the firewall to the top of the throttle body.

The Z6 exhaust manifold is a 2-piece 4-2-1 design as opposed to the 2-piece 4-1 A6 manifold. The A6 4-1 fits the Z6, but there is no reason to use it as opposed to the Z6 4-2-1.

4. Clutch, pressure plate and flywheel…The 90+ setups have a wider surface area then the 88-89 therefore offering more contact area and thus more effective power transfer. The Z6 with stock clutch, pressure plate and flywheel will bolt directly onto 89+ year transmissions. It will not bolt directly onto an 88 transmission unless the proper 88 clutch, pressure plate and flywheel are used (due to the 88s having a different spline count on the input shaft). 92+ transmissions can’t be used due to them being hydraulically activated, and the mount positions on the 92+ transmission being different then the ones on the 88-91 transmissions.

5. The A6 alternator and AC compressor mounts bolt right onto the Z6 thus allowing the use of the A6 alternator and AC compressors.

6. The location of the coolant temperature sensor is on the back of the block for the 88-92 engines (88-91 A6 and 92 Z6) thus if a 92 Z6 is used, no relocation of the wiring for it is required. On the 93-95 Z6, the temperature sensor is on the thermostat cover thus the wiring for it will need to be relocated.

These steps will get the Z6 into the car. If it is decided at this point to use stock CRX Si (A6) electronics, these steps will have to be followed:

1. Modification of the distributor mounts is necessary. Only the top and front mount legs on the A6 distributor will be used, as the rear mount does not match up to the bolt-in location on the Z6 head. Both of the legs on the distributor will need to be modified (cut or enlarged) so as to get the timing correct. Large washers will most likely be needed to make sure positive contact with the head is made. Make sure to put a new o-ring on the distributor where it goes into the head to prevent oil leakage. It is also necessary to use Z6 sparkplug wires.

2. As for fuel injectors, you must use the A6 fuel injectors with the A6 computer (PM6). To do this, simply replace the Z6 injectors with the A6 injectors. Here is another place new o-rings are necessary. The green o-rings on the fuel injectors should be replaced in order to avoid gasoline being forced out around the tops of the injectors, thus creating a fire hazard.

3. In order to use the VTEC, it is necessary to wire some kind of activation switch for it. Various methods can be used. For example an RPM activation switch or an adjustable shift light.  Use of a Zdyne One-Wire VTEC conversion ECU is highly recommended to ease this process. It will give enriched fuel curves for proper VTEC operation as well as allowing a user defined VTEC activation point and other features.

At this point, the engine will run like an A6 but will be VTEC capable assuming an activation switch has been wired up.

OBD0 to OBD1 conversion

This was an ah, interesting, ordeal…yes, ordeal was the correct word. Over all, the process took about 15 hours. Several hours were spent looking over the instructions received from StorminMatt for the process making sure they were correct. They will be listed below. Modifications had to be made to the engine harness and either the dash harness has to be modified or a converter that will allow the OBD1 ECU to be plugged into the 89 dash harness.

Engine Harness conversion
Note: Removal of the engine harness is recommended due to it making it easier to modify the harness. Wire colors will be listed in this manner red/grn (this means red with a green stripe). Many wires can be pulled out of plugs by pushing in the front  (with a small screwdriver, etc) and giving a gentle tug on the back of the wire.

1. The injection resistor must be removed from the circuit. This is because the OBD0 injectors are not compatible with the OBD1 ECU. In order to do this, the yel/blk wire from the green plug on the injection resistor must be pulled. It will be relocated into an open space in a gray 8 wire plug from the OBD1 harness. This OBD1 plug has 8 yel/blk wires leading out from it and has a gray cap on it. Removal of the cap shows that it has an integrated metal clip that connects all the yel/blk wires together.

2. Injector wiring. To use the OBD1 injectors, the injector plugs from the OBD1 harness must be used. Each plug has a different color line (brown, red, light blue and plain yellow…1,2,3,4 injectors respectively) and a yel/blk wire leading from it. The yel/blk wire from each of the injector plugs leads back to the 8 wire plug mentioned in #1. The OBD0 injector plugs must be cut off and the OBD1 injector plugs soldered on. Match the injector colors to each other, as they are the same on both the OBD0 and OBD1 harness. Note: On the OBD0 harness, the wire leading from the injector plug to the injector resistor is red/blk. These wires need not be worried about as they only connects the OBD0 injector plug to the injector resistor.

3. A 4-wire O2 sensor must be added. In order to do this, 3 lines must be added to the harness. One line runs from the O2 sensor plug to the 8 wire plug mentioned in #1, this wire is yel/blk. The second line is a grn/wht line that runs from the O2 sensor plug to any location on the grn/wht wire on the OBD0 harness. The third line is an org/blk line that leads to the ECU. The final wire is the white one. This wire serves the same purpose on both the OBD0 and OBD1 cars. This white wire is the O2 sensor wire itself…on the OBD0 engine harness, it is a single wire and has a rather large plug on it. This plug must be cut off and the white wire for the OBD1 plug soldered on.

4. Distributor rewiring. The lines for the distributor’s 7 wire plug can be pulled on both the engine harnesses. Pull the gray OBD1 7 wire plug for the distributor off the OBD1 engine harness and the replace the 7 wire plug on the OBD0 harness with it. Make sure to match the wires coming from the distributor with the matching colors being put into the 7 wire plug. As for the 2 wire plug, the plug had to be cut off the OBD0 harness and OBD1 plug spliced on.

5. VTEC. One wire must be added to the harness for the VTEC activation wire. It is a grn/yel one-wire plug on the OBD1 harness. This wire must be run into the car and attached to the ECU.

6. VTEC oil pressure sensor. 2 wire plug, one wire black and the other blue/blk. The black wire must be run to a ground and the blue/blk wire runs to the ECU.

That’s it for the engine harness conversion.

Dash Harness conversion
This is the fun stuff. There are two methods of doing this step.
Note: Using a 92 Civic ECU (OBD1) plugs is best for this conversion due to it having all the necessary wires for the Z6 ECU. If 92 ECU plugs cannot be found, try to get the plugs from a Si or EX, otherwise additional wires will need to be added. Should these instructions be used for an OBD1 B-series, a knock sensor wire will need to be added to the plugs (unless the ECU plugs are from an OBD1 Del Sol VTEC are used). It will be mentioned below.

1. Build a conversion harness. The female ECU plugs from a 92 Civic DX auto and the male plugs off an OBD0 ECU. In order to get the plugs off the OBD0 ECU, they can/may be unsoldered or it may be necessary to cut the ECU board with a Dremel tool (equipped with a cutoff blade). After the plugs were taken out and cleaned up, the wires from the OBD1 ECU plugs could be soldered onto the proper pins from the OBD0 plugs. See listing below for proper combinations.

In addition to matching the wires, three wires will have to be routed into the harness to meet up with the OBD1 plugs. These wires are the VTEC wire, the VTEC oil pressure wire and an O2 sensor wire.

2. Cut off the OBD0 ECU wire plugs and splice the wires from the OBD1 ECU plugs to the wires from the OBD0 harness as listed below. You will also have to attach the 3 extra wires as mention above in #1.

Here is the information on the wiring the OBD1 ECU. It is originally by
StorminMatt from CRX Resource. There are several additions that have been made to the listing in the hope of making it more helpful and easy to understand, however, his post has been mostly left intact because he explains it well.

“A number of people have asked me how to change the 1988-1991 ECU plugs to 1992-1995 plugs in order to use a 1992-1995 ECU for any one of a number of applications (SOHC VTEC, 2G B16A, 1992+ B18A/B18B, B17A, B18C, etc.). I figured it would be best to just make one post with this information rather than having to email everybody separately with this information. There are a couple of things to remember here. I personally prefer the numbering system whereby the pins are numbered across rather than the zig-zag system used by Honda. But I realize alot of people may prefer or are used to the zig-zag system. So for each pin (on each plug style), I list two locations for the same pin. The first is given by numbering across. The second (in parenthesis) is by the zig-zag numbering (I hope it is correct). In case I made any errors in conversion AND to make the process of changing the plugs over more goof proof, I also give the color of the wire on the 1992-1995 plug and 1988-1991 plug for the given pins. This should give you a better idea of whether you are connecting the wires together correctly. Also, the first set of pin numbers and wire colors are all on the 1992-1995 plugs and the second, the 1988-1991 plugs.

A plug (1992-1995 plug)

A1 (A1) ----> A1 (A1) Injector 1
brn --------> brn
A2 (A3) ----> A2 (A3) Injector 2
red --------> red
A3 (A5) ----> A3 (A5) Injector 3
lt. blu ----> lt. blu
A4 (A7) ----> A14 (A12) Main Relay
grn/yel ----> grn/blk
A5 (A9) ----> A5 (A11) EACV
grn/wht ----> blu/yel
A7 (A13) ---> B13 (B6) Check Engine Light
grn/org ----> grn/org
A8 (A15) ---> B2 (B3) A/C Clutch Relay
blk/red ----> yel
A11 (A21) --> B8 (B15) Ignition Unit Signal
red/grn ----> wht
A12 (A23) --> A9 (A2) Main Relay
blk --------> blk
A13 (A25) --> A6 (A13) Main Relay
yel/blk ----> yel/blk
A14 (A2) ---> A4 (A7) Injector 4
yel --------> yel
A15 (A4) ---> (VTEC) grn/yel at on the engine harness, your choice elsewhere
org/wht ----> (your choice)
A16 (A6) ---> (O2S heater) to orn/blk on engine harness, your choice elsewhere
org/blk ----> (your choice)
A17 (A8) ---> A15 (A14) Main Relay
grn/yel ----> grn/blk
A19 (A12) --> B12 (B4) Radiator Fan Relay
yel/grn ----> yel/grn
A21 (A16) --> B3 (B5) Alternator
wht/yel ----> wht/yel
A23 (A20) --> A11 (A6) Purge Control Solenoid
red --------> grn
A24 (A22) --> B9 (B17) Ignitor Unit
red/grn --------> wht
A25 (A24) --> A10 (A4) Ground
blk --------> blk
A26 (A26) --> A17 (A18) “Multiground”
blk/red ----> blk/red

B Plug (1992-1995 plug)

B1 (B1) ----> A7 (A15) Main Relay
yel/blk ----> yel/blk
B3 (B5) ----> B14 (B8) A/C Switch
blu/red ----> blu/red
B5 (B9) ----> B7 (B13) Main Relay
blu/wht ----> blu/wht
B6 (B11) ---> B15 (B10) **
org --------> org
B7 (B13) ---> C2 (C3) **
org/blu ----> org/blu
B8 (B15) ---> C1 (C1) **
blu/grn ----> blu/grn
B9 (B2) ----> A16 (A16) Multiground
brn/blk ----> brn/blk
B13 (B10) --> B18 (B16) Vehicle Speed Sensor
yel/blu ----> yel/red
B14 (B12) --> B16 (B12) **
wht --------> wht
B15 (B14) --> C10 (C4) **
wht/blu ----> wht/blu
B16 (B16) --> C9 (C2) **
blu/yel ----> blu/yel

D Plug (1992-1995 Plug - NO C plug on 1992-1995 Plugs)

D1 (D1) ----> B1 (B1) Hazard
wht/blu ----> wht/grn
D2 (D3) ----> (Knock Sensor) B-series engines only!
red/blu ----> (your choice shielded wire)
D5 (D9) ----> B17 (B14) Alternator
pnk --------> blu
D6 (D11) ---> C4 (C7) Throttle Position Sensor
red/blu(or pastel green)  ----> red/blu
D7 (D13) ---> C11 (C6) Coolant Temperature Sensor
red/wht ----> red/wht
D8 (D15) ---> C3 (C5) Intake temperature
red/yel ----> red/yel
D9 (D17) ---> C6 (C11) Map Sensor
wht --------> wht
D10 (D19) --> C8 (C15) Map Sensor
yel/grn ----> yel/red
D11 (D21) --> C15 (C14) Map Sensor
grn/blu ----> grn/wht
D12 (D2) ---> C13 (C10) Brake Switch
grn/wht ----> grn/wht
D13 (D4) ---> B20 (B20) Service Connector
brn --------> brn
D14 (D6) ---> (VTEC Pressure Switch) Blue/blk wire in engine harness
org/blu ----> (your choice)
D16 (D10) --> B10 (B19) Electronic Load Sensor
grn/red ----> grn/red
D18 (D14) --> C16 (C16) O2 Sensor
wht --------> wht
D21 (D20) --> C7 (C13) Throttle Position Sensor
yel/wht ----> yel/wht
D22 (D22) --> C14 (C12) Coolant temp/TPS/O2/etc…ground kind of thing
grn/wht ----> grn/wht

The pins marked ** connect to the distributor sensors (crank angle, TDC, and CYP). The reason I marked these is that while 1988-1991 and 1992-1995 cars both use the same color wires collectively for these sensors (org, org/blu, wht, wht/blu, blu/grn, blu/yel), wires of a given color do NOT necessarily connect to the same sensors in the 1992-1995 cars as in 1988-1991 cars. So if you check the Hasport pin-out, the connections I gave will be incorrect. However, it is actually easier to just match up like colors. If you do this, just remember to match the proper colors on the distributor plug as well. In other words, the org wire on the 1988-1991 engine harness goes into the same spot on the 1992-1995 distributor plug that the org wire went to on the 1992-1995 engine harness.
Just don't confuse the fat white wire with this thin white wire on the distributor plug of the 1988-1991 engine harness. The fat white wire on the 1988-1991 harness goes where the fat yel/grn wire on the 1992-1995 harness went (on the 1992-1995 distributor plug). But the thin white wire on the 1988-1991 harness goes where the thin white wire on the 1992-1995 harness.”

To clarify the information on the distributor wiring…match the like color wires at the distributor plugs (for example: org with org) as well as at the ECU. In other words, the same color should go from distributor clear to the ECU.

Other assorted necessary items

Fuel injectors: Model #4106 and #4107 fuel injectors were available for this swap from personal stock. The fuel injectors used in this swap in particular are #4107’s. It is not know what year these injectors are; they could be either 93 or 94 model year injectors as both year injectors were available. The #4107 injectors were used because they worked with the 95 P28 ECU used. The #4106 injectors did not work with the 95 P28 ECU. It is unknown as to why the #4106’s did not work, but alas, they did not. The utmost effort should be made to get matching injectors for the P28 ECU to be used.