I have a 1989 four door civic Dx and I want to put A 1989-1991 civic Si motor in it.
I know the motor bolts up to all the stock mounts but, I was wondering if the wiring
harness needs to be changed.? I know I need to put the Si computer in it but can I get away with out changing the whole harness? And last but not lest can I use the Dx tranny or should I change that as well? Thanks to everyone who trys to help.

 

you will need to use your dx harness, but make a few changes. this info is taken from a previous post by zcivicz

DPFI TO MPFI CONVERSION
complete intake manifold (TB, fuel rail, injectors, all sensors!)
injector resistor
88-91 Si ecu
88-91 Si distributor
and an si coolant hose to connect the manifold and the block u can use ur stock and cut it if ur cheap

its pretty easy! drain the raidiator and all then take off the intake manifold and put the si intake manifold on and rewire everything. dissconect all the plugs from all the sensors and the injectors make sure u diconnect the coolant lines from the intake and there is one bolt that holds the manifold to the block underneath u wont see it unless u know about it

In order to convert your dual point injection DX to multi-point injection you will need 4 injector plugs, an injector resistor box, extra wire, and electrical tape(heat shrink is best).Also, when doing this conversion I would highly recommend soldering all connections and heat shrinking them. It is good to have an extra multi-point injection engine harness laying around to take plugs off of(injector plugs, injector resistor box plug, and distributor plug u can use ur stock dist plug if u cut one off another dx dist and use it to plug in but ull need a 2 wire plug for the ca sensor).

Pins B10 and B12 are empty. Unused pins can be taken from B2 or B11. Sometimes there is a unused wire at B12.
Cut orange and white wires off at C1 and C2 and connect them to wires added at B10 and B12. Orange-B10. White-B12. Leave enough wire for next step.
Run wires from C1 and C2 on the ecu into the engine compartment. Label these wires for later use.
Cut wires at A3 and A7 leave excess for later use. Run these wires into the engine bay and label them to be used later on .

Under the Hood
TPS and EACV plugs are too short and must be extended.
Be sure to switch green/white and yellow/white wires on TPS since the dx turns the opposite way.
Injectors and injector resistor box
Connect the yellow/black wires from the two DX injector harnesses and run it to the yellow/black wire on the injector resistor box.
Connect the yellow wire from the DX injector to the #1 injector (brown wire).
Connect the red wire from the DX injector and run it to the #3 injector (blue wire).
Connect the A3 wire to the #2 injector (red wire).
Connect the A7 wire to the #4 injector (yellow wire).
Connect the 4 red/black wires from injector resistor box to each injector.

Cylinder position sensor
Connect C1 to blue/green wire on cylinder position sensor plug.
Connect C2 to blue/yellow wire on cylinder position sensor plug
the rest of the wires are color matched. dx to the si wires


As for the tranny...you can use your dx tranny but i think the si has closer gear ratios if you are interested...hope this helps

 

These instructions are remarkably similar (if not cut & pasted) to instructions that I give in my DX to ZC article on the Hybrid main page.

Anyways, those instructions will work. Good luck.

-kenji

 

Tanks for all your help that is everything I needed to know, now I start the conversion.Once again thanks for every thing