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DPFI to MPFI conversion

All 1988 to 1991 DX and LX Civics and CRXs came from the factory with Honda’s ubiquitous dual-point EFI system. These cars are known for their low price tags and great gas milage. Unfortunately, they’re also renowned for less-than-stellar horsepower and complete lack of tuning potential. The ‘88-’91 cars that fall under this category include the following:

*Fourth-generation Civic DX and LX four-doors

*Fourth-generation Civic Standard,

DX two-door hatchback

*Second-generation CRX DX

The good news is that dropping a big power-producing drive train into one of these feeble Civics or CRX is incredibly easy. In fact, any one of the following engines can be bolted in with relative ease.

*1988-’91 Civic EX or Si 1.6 liter SOHC (d16a6)

*1988-’91 CRX EX or Si 1.6 liter SOHC (d16a6)

*1988-’91 JDM Civic or CRX 1.6 liter DOHC (zc)

In addition, the potent 1.8 liter DOHC (b18a) power plant from any 1990-’93 Integra is also a snap to drop in place, requiring only a tad more effort, as well as a bolt-in engine mount kit.

One of these reasons these transplanted engines create more horsepower is their multi-point EFI systems. In simple terms, multi-point EFI is an intake system with an individual fuel injector dedicated to each cylinder, rather than one or two common injectors located further upstream in the manifold plenum. Better fuel control can be achieved with separate injectors pointing right down the barrel of each intake port than with common plenum-type injectors. In addition, Honda mulit-point injection throttle bodies are typically larger than dual-point throttle bodies. Bigger throttle bodies allow for more airflow, which of course means more power.

That’s the good news. The bad news is many people get bogged down in the wiring changes when trying to install mulit-port EFI engines in their dual point cars. To walk us through this mysterious wiring process, we once again turned to Brian Gillespie at HASport for his expert advice. Gillespie and his brother Keith at Honda Auto Salvage in Phoenix have been dropping big engines into little Hondas for nearly a decade. These guys have seen and done it all.

We discovered the EFI wiring changes are actually quite simple__that is, if you attack the problem in a logical fashion. Gillespie says the key to successful wiring conversion is to modify the existing dual point harness. The majority of wires needed are already there. In fact, only 4 wires are missing. If you try to use the mulit-port injection harness that came with the new engine, you’ll notice many differences, including some wires originating from opposite sides of the engine bay.

You also have to take your time and fully understand what you’re doing and why. Take it one step at a time. If you go slowly, and stay organized, the wiring changes required to switch your car to mulit-point EFI shouldn’t take more than a couple of hrs.

STEP 1: CYLINDER SENSOR WIRING:

There are two major parts to connecting a multi-point EFI engine in a dual-point equipped chassis. They are: (1) cylinder sensor wiring and (2) fuel injector wiring. The first one (cylinder sensor wiring) is the easiest. The second one (injector wiring) is a bit more complicated. Let’s take a look at the easy part first.

Honda Multi-point EFI engines are equipped with cylinders sensors. These sensors detect the position of the number 1 cylinder and are used for controlling the sequencing of fuel injecton to each cylinder. Obviously fourth-generation Civics and second-generation CRXs didn’t need this sensor because the dual-point EFI systems were non-sequential. They just squirt fuel into the common manifold plenum as required and whichever cylinder was on the intake stroke got gas. It’s simple and reliable, but not capable of producing as much power as a true sequential system.

To get the multi-port cylinder sensor hooked up, you must first relocate two existing wires at the ECU in the passenger foot well. Move the wire that goes to pin C1 to pin B10, and move the wire that feeds pin C2 to pin B12. These changes are for the crank angle sensor, so be careful. Don’t get these mixed up or the ignition timing will be severely retarded.

Every donor engine we listed, with the exception of the JDM ZC, has the cylinder sensor inside the distributor. If you have a ZC engine, the sensor is on the passenger’s end of the exhaust cam. Regardless of location, the sensor needs two wires feeding it. There will be a connector on the distributor (or near the end of the cam on ZC engines) with two unused pin positions. One of the wires at the connector will be blue with a green stripe; the other will be blue with yellow stripe. To keep the coding correct, Gillespie recommends you follow Honda’s wire color system. Add feed wires to the connector, matching the colors as shown in the wiring diagram.

The two new wires you just added must now be connected to the ECU in the footwell. Gillespie strongly recommends you incorporate a connector at the firewall in case you ever want to remove the engine or sensor from the car. In other words, don’t use single, one-piece wires that run all the way from the cylinder sensor, through the firewall, and to the ECU. If you do, you’ll regret it. Locate the new connector on the right -hand shock tower like Honda does so it’s easy to find.

Now, being careful to use the same color wires on the other side of the connector, make the final cylinder sensor connections inside the car. Connect the blue with green stripe wire to the C1 pin on the ECU. Then connect the blue with yellow stripe wire to the C2 pin on the ECU.

The only thing left to do is a quick pin swap at the Throttle Position Sensor (TPS). Because the TPS on the new engine works in the opposite direction from the old engine’s unit, you must swap the two outside wires at the TPS. If you don’t, the ECU will think the engine is at Wide Open Throttle (WOT) when it’s at idle, and vice versa.

That’s it. You’re done with step one.

STEP 2: INJECTOR WIRING

OK, now for the slightly harder part: getting electrical power to the fuel injectors. If you hadn’t noticed by now, the old dual-point engine had--you guessed it--two fuel injectors. The new engine has four. The crux of this part of the injector wiring exercise is to get ECU-controlled power distributed to each of the four injectors.

The first bugaboo, however, is the old dual-point Honda EFI system used something called high-impedance injectors. The new injectors on the multi-point engines are low-impedance units. This means you must step down the voltage to the correct levels, or the injectors won’t function correctly. To do this, you have to wire a Honda resistor box in series with the power feeds to the injectors. Here’s how it’s done.

Mount a new resistor box on the left-hand (driver’s side) shock tower, but first supply power to the resistor box connector. Taking larger gauge yellow wire with black stripe from the existing connector located in the engines harness on the left-hand shock tower, does this. This is the wire that provided power to the main injector on the old dual-point engine.

Next, run a brown wire from the resistor box connector to the No. 1 injector. It will replace the yellow wire that was the secondary injector wire. Then run a light blue wire from the connector to the No. 3 injector, replacing the red wire that was the primary injector wire.

The No. 2 and 4 injectors, however, are handled in a slightly different manner. Run a red wire from the No. 2 injector to A3 pin on the ECU. Also, run a yellow wire from the No. 4 injector to A7 on the ECU. We’ll also run these wires through the same connector at the right-hand shock tower the cylinder sensor connected through. This will allow us to disconnect the harness if we ever have to remove the engine. To do this, you must unplug the existing two wires plugged into pins A3 and A7. These aren’t needed anymore with the new engine, and can simply have their ends terminated with some heat-shrink tubing.

Finally, wire up the four power feeds from the resistor box connector out to the four injectors. In this case all four wires are red with black stripes.

Hey, you’re done. Welcome to the modern world of multi-point electronic fuel injection. And, by the way, welcome to more horsepower, too.