Wiring DSM Low-Impedance Injectors into a Honda D-Series with Inline Resistors

Source a set of four 450cc DSM injectors; both the first-generation blue-top and the newer second-generation black-top versions work equally well here. Expect to pay roughly $40-75 for a used set. These are low-impedance (peak-and-hold) injectors and draw more current than the high-impedance (saturated) units a Honda expects. As a rough reference, peak-and-hold injectors measure about 1.7-3.0 ohms while saturated ones measure about 10-16 ohms. If your car already has a factory resistor box, such as 4th-generation MPFI cars or some SI models, the injectors can plug in without the inline resistors described here; otherwise continue with this procedure. Plan on tuning the ECU afterward, since the added flow will otherwise upset the air-fuel ratio.

Each DSM injector has a small locating tang beside its electrical connector that stops a Honda plug from seating. Trim this tang off with a hobby or pocket knife; it does not need to look neat, only to clear enough material for the clip to snap on. On the harness side, DSM, OBD0, and OBD1 injector clips all mate to these injectors once you shave down the plastic spacers inside the clip. OBD2 clips have a narrower pin spacing and will not fit, so if your car is OBD2, wire in OBD1 injector clips instead.

The DSM injector body and its lower O-ring sit wider than the stock Honda parts, so the injector will not drop fully into the manifold seat without adjustment. Two approaches work. Either reduce the O-ring diameter by holding it on the injector (or a similarly round object) and turning it lightly against a grinding wheel or Dremel drum sander until it seats snug and flush, or place each O-ring in the manifold first and let the fuel rail compress the injectors evenly onto them as you tighten it down. Whichever method you use, smear a little oil or grease on the rubber so it does not tear during assembly, then test-fit each injector for a tight, leak-free seat.

Find the injector power connector, often called the dead plug, unplug it, then peel back the wire loom and tape to expose the injector wiring. On 5th-generation cars it sits near the driver-side strut tower; on other generations it may be tucked behind the intake manifold or at the back of the engine, so its exact position varies. This plug is not actually dead: one feed wire supplies 12 volts and an internal jumper distributes that power across the wires to all four injectors (there are five wires here for four injectors, the fifth being the 12-volt feed). OBD2 cars have no dead plug at all, so ignore any reference to it and follow the rest of the procedure.

Set a multimeter to its resistance or continuity range. Probe the yellow/black wire inside one injector clip with one lead, then touch the other lead to each wire at the power connector until you find the matching pair; the continuity buzzer will sound, or you will read a very low resistance. That is the wire for that injector. Note that with the key on you will typically see power on only one wire at the connector, which is normal, because the resistors (or a factory resistor box) complete the circuit to the remaining injectors.

Cut the injector wire you just identified. Coat each freshly cut end with a thin layer of solder, known as tinning, so it will bond cleanly to the resistor leads. A dab of flux on the strands helps the solder flow and stick. Use rosin-core, acid-free solder only; acidic or corrosive solder will slowly eat the joint and cause intermittent faults.

Before making any joint, slide a length of heat-shrink tubing onto each cut end so it stays captive on the wire. Then solder one 10 ohm 10 watt resistor between the two cut ends, bridging the gap in the injector wire. The resistor has no polarity, so either orientation is fine. Keep each joint mechanically solid and fully wetted with solder.

Slide the pre-loaded heat-shrink over each solder joint and shrink it with a heat gun or lighter for a moisture-tight seal. Work through the remaining injector wires the same way until all four carry an inline resistor. For a tidy result, gather the resistors into a small project box mounted to the body or strut tower, bundle the wiring with zip ties, and refit the loom. If you expect to swap injectors later, for example at inspection time, add Molex connectors at the ends so the injectors detach without unsoldering.

With everything reassembled, turn the ignition to the on position so the fuel pump primes and pressurizes the rail, then inspect every injector seat and fuel connection for leaks. Start the engine only after confirming there are none. Because the new injectors flow far more than stock, have the ECU tuned before driving to avoid running dangerously lean or overly rich.