Many people get confused when it comes to upgrading or replacing fuel injectors, especially concerning OBD2 systems. A common misconception is that the OBD connector type is the primary concern when selecting fuel injectors. However, the real issue that can lead to serious problems, even frying your system, is the injector’s resistance – not whether it’s OBD1 or OBD2.
There are fundamentally two types of fuel injectors based on their electrical resistance: high resistance (saturated) and low resistance (peak & hold). Understanding the difference is crucial for maintaining your vehicle’s fuel system integrity.
High Resistance (Saturated) vs. Low Resistance (Peak & Hold) Injectors
High Resistance or Saturated Injectors: These injectors are designed to be turned on and held open with a continuous current. They have higher internal resistance, typically around 12-16 ohms. OBD2 systems are generally designed to work with saturated injectors.
Low Resistance or Peak & Hold Injectors: These injectors use a different strategy. They receive a high current “peak” to rapidly open, and then the current is reduced to a lower “hold” level to keep them open. This allows for faster response times and more precise fuel delivery, especially in performance applications. They have lower internal resistance, usually around 2-5 ohms.
The critical point is that a system designed for high resistance injectors delivers current accordingly. If you install low resistance injectors in such a system without modification, you’ll be sending too much current through them continuously.
The Risk of Mismatched Injectors: “Frying” Your System
If you mistakenly install low resistance peak & hold injectors in a system designed for high resistance saturated injectors, you risk “frying” the injector driver circuit in your car’s ECU (Engine Control Unit). This is because the ECU is not designed to handle the higher continuous current draw of low resistance injectors.
This damage is not related to the OBD connector type. You could use OBD1 or OBD2 connectors, but if you mismatch the injector resistance type, damage can occur. The original confusion often arises because some performance upgrades involve using low resistance injectors, and these might sometimes be associated with older OBD1 systems.
Resistor Boxes: The Solution for Low Resistance Injectors
For situations where you need to use low resistance peak & hold injectors in a system designed for high resistance saturated injectors (often for performance upgrades requiring higher fuel flow), a resistor box is necessary.
A resistor box is essentially a set of resistors wired in series with the low resistance injectors. This added resistance mimics the electrical load of high resistance injectors, protecting the ECU from overcurrent and allowing the low resistance injectors to function correctly. As mentioned in the original text, using a resistor box from a DX Civic when upgrading to peak & hold injectors on a Honda Integra (Teg) is a common example.
OBD Compatibility vs. Electrical Compatibility
It’s essential to differentiate between OBD connector compatibility and electrical compatibility (injector resistance). While OBD2 is the standard for modern vehicles, and OBD1 is older, these terms primarily refer to diagnostic protocols and connector shapes, not injector resistance types.
You can find both saturated and peak & hold injectors in both OBD1 and OBD2 connector styles. The connector type ensures physical fitment, but it doesn’t guarantee electrical compatibility.
Choosing the Right Injectors for Your OBD2 System
For most OBD2 vehicles and standard replacement scenarios, saturated (high resistance) injectors are typically the correct choice. They are designed to work seamlessly with the factory ECU without requiring modifications like resistor boxes.
If you are considering performance upgrades that necessitate higher fuel flow and are looking at low resistance injectors, you must ensure you incorporate a resistor box into the wiring to protect your ECU. Always verify the resistance type of the injectors you are installing and match them appropriately to your vehicle’s fuel system design.
