The MPFI Swap
This is my DX motor with Si MPFI. I will try to get a few more pics and close ups of the installation soon.
The parts you will need:
88-91 Si intake manifold (Get all the sensors and throttle body)
Intake manifold brace (The dx brace is different)
ECU-88-91 si or 88-89 teg
Injector Resistor 88-91 si or 88-89 teg
88-91 si distributor
Extra wire or a wiring harness from a si
Some assorted connectors can be custom made or sourced from the si wiring harness
Intake manifold and throttle body gasket
Injector o-rings and seals
Hoses may be required in some instances (UPDATE: There is a hose that is different between the dx and si on the distributor side of the intake manifold. It has a 180 degree bend [Looks like a U] and it goes from the intake to the head and will be needed.)
Preparation:
I would give the intake manifold and throttle body a good cleaning using a carb cleaner spray. Make sure that the parts are all clean before putting them on. Then put the new seals and gaskets on or have them handy.
Removal:
First thing is to drain the radiator. I would get some fresh coolant(The Dexcool type is best for aluminum) to put back in after you finish the swap.
Next you will want to remove all the hoses, wiring, and vacuum lines that goto the dx manifold. Make sure you mark them or have a service manual handy to know where they go after you put the new manifold on the car.
Then remove the old manifold and clean up your mating surfaces. The brace bolts are a pain to get at but not that difficult.
While its off:
I would then extend the throttle position sensor(TPS) plug about 8 inches making sure that you switch the wires per the wiring instructions. Also extend the EACV plug wires about 5 inches. Another wiring change to do is adding the appropriate wires for the injectors now. The wiring instructions come in handy here as well. You will be glad you did this before you installed the manifold. I know from experience.
Then install the new manifold and reconnect the hoses and vacuum lines and connections.
You then need to finish up the wiring.
Wiring Instructions:
4G Dx to Si wiring conversion
by kenji modifyed by C_Rexboy
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, a wire stripper/cutter, heatshrink and/or electrical tape, and some patience. Also, when doing this conversion I would highly recommend soldering all connections and heatshrinking them. If you do not have access to heatshrink neatly wrapped electrical tape will do just fine. It is also extremely helpful to have an extra multi-point injection engine harness laying around to take plugs from (i.e. injector plugs, injector resistor box plug, and distributor plug). Listed below is a straightforward and easy to follow set of instructions to help you complete your DX to Si manifold swap.
Inside car @ ECU
Pins B10 and B12 are empty. Unused pins can be taken from B2 or B11. Some models have a wire located 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 (direct ECU connection) into the engine compartment. Label these wires for later use.
Cut wires at A3 and A7 leaving plenty of wire. Run these wires into the engine compartment and label them for later use.
Before installing manifold
TPS and EACV plugs are too short and must be extended.
Be sure to switch green/white and yellow/white wires on TPS
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.
These wires are off the si distributor so connect them there.
Thats it. Double check everything and start it up. Good luck!
Okay next weekend you get to replace the timing belt!
But why you ask? Because you might as well do it while you have it apart to put the si cam in.
Oh yeah and don't forget to replace the water pump too!
I have installed an Si cam, and it is the icing on the cake. Just looking at the two cams you can see the si cam is much more aggressive and it really brings the top end to life. The only difficult thing is to properly degree in the cam. I had to advance it 1 or 2 teeth on the cam sprocket to get it to line up and give me good ignition timing. I really need an adjustable cam gear now! It takes a while to get it right but it helps make a good deal more of the stuff you crave, POWER.
Update 10-19-00: I ran the car for a 16.7 @81.9mph about 4 months ago (Baseline before MPFI swap
17.5@~77). Since then I have put the adjustable cam gear on and advanced the timing 4 degrees and the motor runs so much stronger now. Pulls harder than my si did.