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MPFI swap


The Effin Guide to MPFI swaps
The MPFI(multi point fuel injection) is the first step to making power in a dual point fuel injected (DPFI) equipped car. While the stock DX makes 92 hp, this conversion typically results in 100-102 hp with improvements across the entire RPM range. While still a few horsepower shy of a full Si because of .1 liter difference in displacement, the DX is a few pounds it about equals out. The MPFI system also responds better to the regular bolt on power modifications.

The parts you will need:
88-91 Si intake manifold and gasket (Get all the sensors)
Intake manifold brace (The DX brace is different)
ECU: 88-91 Si or 88-89 teg
Injector Resistor Box 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
Throttle body and gasket
Injector o-rings and seals
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.
The stock DX airbox will not fit properly. Either get a Si box, an aftermarket cone style intake or plan on some ghetto fabrication
I would give the MPFI intake manifold and throttle body a good cleaning with carb cleaner.

Now would be a good time to do any port/polish work on the intake manifold. Just don't go overboard on the polishing as a slightly rough surface encourages some turbulence/air tumble that is ideal for combustion.

Drain the radiator.
Remove all the hoses, wiring, and vacuum lines that go to 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 the mating surfaces.
While the DX manifold is off:
Extend the throttle position sensor (TPS) plug about 8 inches making sure that you switch the wires per the wiring instructions.
Extend the EACV plug wires about 5 inches.
Add 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.
Then install the new manifold and reconnect the hoses and vacuum lines and connections.

Now you need to finish up the wiring...

Wiring Instructions:
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.

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 be satisfactory

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 MPFI 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.

That's it. Double check everything and start it up. Good luck!

Great write up! i'm ordering a complete multipoint conversion kit. (dizzy, manifold, ecu, fuel rail, injectors, etc) all came off a crx si. will it  be just plug and play?

no. youll need to work on the wiring. Forum Index -> Write Ups & Tech Info
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