Dual Point Fuel Injection (DPFI) is a throttle-body injection system utilized on early Honda D-series engines. Unlike Multi-Point Fuel Injection (MPFI), which utilizes one injector per cylinder, the DPFI system relies on two injectors located within the throttle body assembly to deliver fuel to all cylinders simultaneously.

System Operation#

The DPFI system functions as a semi-sequential injection setup where fuel is atomized at the throttle body and distributed through the intake manifold.

Note

DPFI systems are often identified by their distinct two-injector throttle body housing, which differs significantly from the four-injector rail configuration found in MPFI systems.

Key Components#

• Throttle Body: Houses the two fuel injectors and the idle air control components.
• Fuel Injectors: Two low-impedance injectors responsible for the entire fuel delivery requirement of the engine.
• ECU: Controls the duty cycle of both injectors based on inputs from the MAP sensor, TPS, and coolant temperature sensor.

Conversion to MPFI#

Many enthusiasts perform an MPFI conversion to improve fuel atomization, throttle response, and overall engine efficiency. This process typically involves:

1. Replacing the DPFI intake manifold with an MPFI intake manifold.
2. Installing a four-injector fuel rail and wiring harness.
3. Updating the ECU to a version compatible with MPFI operation.
4. Modifying the engine wiring harness to accommodate the additional injector signals.

Caution

Converting from DPFI to MPFI requires significant wiring modifications, including the addition of two injector control wires and the reconfiguration of the resistor box wiring. Ensure all connections are soldered and heat-shrunk to prevent electrical resistance issues.