A Resistor Box is required when utilizing Peak and Hold (Low-Impedance) fuel injectors on Honda ECUs that were originally designed for high-impedance injectors. The box limits the current flow to the injectors to prevent damage to the ECU driver circuits.

Technical Overview#

• Purpose: Limits current draw for low-impedance (2–5 $\Omega$) injectors to match the requirements of ECU driver circuits designed for high-impedance (12–16 $\Omega$) injectors.
• Application:
  • OBD0: Factory-equipped with a resistor box.
  • OBD1/OBD2: Not factory-equipped. An external box must be added if swapping to low-impedance injectors.

Wiring Procedure#

The resistor box is wired in series between the 12V ignition power source and the fuel injectors.

1. Locate Ignition Power: Identify the +12V switched power wire feeding the injector rail harness.
2. Mounting: Secure the resistor box in a location with adequate airflow (the engine bay firewall is the standard factory location).
3. Wiring:
   • Cut the +12V power supply wire leading to the fuel injectors.
   • Connect the +12V power source to the input of the resistor box.
   • Connect the output side of the resistor box to the injector harness side (power side).
   • Ensure all solder joints are sealed with heat-shrink tubing to prevent corrosion or shorts.

Verification#

After installation, use a multimeter to verify that the resistance between the injector plug and ground (on the power side) now reflects the added resistance of the resistor box.

Warning: Failure to use a resistor box with low-impedance injectors will result in excessive current draw, likely causing the fuel injector driver transistors in the ECU to overheat and fail.