Mercedes Mullins
Fuel injectors are valves controlled by the ECU, which sends timed electrical signals called pulse widths. The two main types of fuel injectors are peak and hold and saturated. Peak and hold injectors exhibit less electrical resistance than saturated injector coils. When low impedance injectors are incompatible with your ECU, an injector resistor box can be used. This article will explain how to wire in a resistor on fuel injectors.
How to wire in a resistor on fuel injectors
| Characteristics | Values |
|---|---|
| Types of fuel injectors | Peak and hold, Saturated |
| Types of injectors by resistance | Low impedance, High impedance |
| Resistance of peak and hold injectors | 2-3 ohms |
| Resistance of saturated injectors | 12 ohms |
| Resistance of high-Z injectors | Greater than 8 ohms |
| Resistance of low-Z injectors | Less than 8 ohms |
| Tools needed for wiring | Noid light, Multimeter (volts & ohms), 10 MM socket & extension, Ratchet |
| Power wire colour | Red |
| Voltage required | 12 volts |
| Voltage tolerance | +/- .5 volts |
| Non-power wire colour | Not specified; non-red |
| Resistance across two contacts inside the electrical connector | 11-16 ohms |
| Types of resistors | Radio Shack type 10 Ohm 10 Watt, 20 Watt 1 |
| Resistor placement | 2 to 4 inches from the injector |
| Resistor wire | Powered wire |
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What You'll Learn
- Using a multimeter to check for 12 volts on the red power wire
- Locating the driver-side harness connectors near the brake master cylinder
- Connecting the resistor box's remaining power wire to the cut injector signal wires
- Identifying the difference between peak and hold and saturated fuel injectors
- Using an ohmmeter to set the low resistance scale and measure the resistance of each injector
Using a multimeter to check for 12 volts on the red power wire
Firstly, you need to turn off all power to the plug, including any connected circuits. Then, set the mode on your multimeter to the correct voltage setting. If you are measuring AC voltage, use the section marked with a "V" and a wavy line, indicating the AC waveform. If you are measuring DC voltage, use the section marked with a "V" and a straight line, indicating DC waveform.
Now, it's time to connect the probes. The black probe is the neutral probe and is usually plugged into the "COM" or common port. The red probe is the positive or "hot" probe and is plugged into the port for the unit you are measuring, which could be "VΩmA", "VΩ", "V", or a port labelled for DC voltage. Ensure that the probes are plugged into the correct ports, as reversing them can result in a negative reading.
Once the probes are connected, carefully touch the black probe to a known good ground, and then touch the red probe to the "hot" conductor. You can then touch the probes to the neutral conductor to measure the voltage. If you are measuring between the "hot" and "neutral" conductors, you should get a reading of about 120 volts. If you are measuring between the ground and "neutral", the reading should be 0 volts.
It is important to note that working with live circuits can be dangerous, and it is recommended to use a non-contact voltage detector for simpler tasks.
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Locating the driver-side harness connectors near the brake master cylinder
To locate the driver-side harness connectors near the brake master cylinder, you must first identify the fuel injectors. Typically, fuel injectors are mounted on the intake manifold, near the cylinder head. They are often cylindrical in shape with a wiring connector attached.
Once you have identified the fuel injectors, you can begin to trace the wires. You will likely find a bundle of wires leading from the fuel injectors to a larger connector, which is part of the fuel injector wiring harness. This harness typically runs from the fuel injectors to the engine control unit (ECU) and is located within the engine bay.
The connector itself is usually a multi-pin connector with a locking mechanism. To release the locking mechanism, you may need to press or pull a tab or clip, depending on your vehicle. Refer to your vehicle's repair manual for specific instructions.
After releasing the locking mechanism, gently pull the connector apart, being careful not to damage the wiring or pins. Once the connector is separated, you can then remove the entire wiring harness. The harness may be secured to the engine bay by clips or clamps, which can be released using a flathead screwdriver or an appropriate tool.
With the harness removed, you can now access the driver-side harness connectors near the brake master cylinder. It is important to work in a well-lit area and wear eye protection to prevent any debris or sparks from entering your eyes. Additionally, be cautious of hot components, such as the engine and exhaust system, and avoid touching them.
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Connecting the resistor box's remaining power wire to the cut injector signal wires
Once you have your resistor box, the process is relatively simple. First, locate the driver-side harness connectors near the brake master cylinder. Using a multimeter, find the four wires that lead to the injectors. Cut these wires and connect the injector-side wires to the resistor box's black wires; the order doesn't matter.
Now, connect the resistor box's remaining power wire to the cut injector signal wires. This will provide them with their 12V power signal. Ensure that each injector has 12 volts +/- .5 volts. It's worth noting that Honda fuel injectors rely on constant power for their pulse widths, so the ECU supplies the ground, and the injectors open and close based on ground signals from the computer.
It's important to note that there are two types of Honda fuel injectors: peak and hold, and saturated. Peak and hold injectors, also known as low impedance injectors, exhibit less electrical resistance than saturated or high impedance injectors. Typically, peak and hold Honda injectors will have a resistance of 2 to 3 ohms, while saturated ones measure around 12 ohms.
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Identifying the difference between peak and hold and saturated fuel injectors
Fuel injectors are valves controlled by the ECU (Electronic Control Unit) by timed electrical signals called pulse widths. There are two main types of fuel injectors: peak and hold, and saturated. The difference between the two is the amount of resistance exhibited.
Peak and hold injectors, also known as low impedance injectors, exhibit less electrical resistance than saturated injectors. Peak and hold injectors will typically have a resistance of between 2 and 5 ohms, while saturated injectors, also known as high impedance, will measure around 12 ohms. Peak and hold injectors are usually used in aftermarket high-performance systems, as they are more expensive and complex than saturated injectors. They require a higher current to function, which is supplied by the ECU, and this higher current can provide a more stable opening and closing time for the injector, even when working against high fuel pressure.
Saturated injectors are simpler, more common, and have a slower response time than peak and hold injectors. They are typically used in domestic production ECUs and have a longer lifespan due to their lower current and cooler components.
Peak and hold injectors require a resistor box or an ECU that can control the current without the box. The resistor box steps down the current between the ECU and the fuel injectors.
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Using an ohmmeter to set the low resistance scale and measure the resistance of each injector
When working with fuel injectors, it's important to understand the difference between peak and hold (low impedance) and saturated (high impedance) injector coils. Peak and hold injector coils exhibit less electrical resistance than saturated injector coils. This difference in resistance is crucial when it comes to wiring and troubleshooting fuel injectors.
To set the low resistance scale and measure the resistance of each injector, you'll need an ohmmeter. This tool is essential for accurate measurements. Start by setting the ohmmeter to the low resistance scale, typically measured in ohms (Ω). This scale is necessary due to the low resistance values expected in fuel injectors. Connect the ohmmeter to the fuel injector you want to test. Ensure you're measuring across the two contacts inside the electrical connector of the injector.
The ideal resistance reading will depend on the type of injector. For instance, Honda peak and hold injectors typically have a resistance between 2 and 3 ohms, while saturated injectors measure around 12 ohms. If your readings fall outside the expected range for your specific injector type, it may indicate a faulty injector.
Additionally, it's important to ensure that each injector has the correct voltage. Using a multimeter, check for 12 volts on the red power wire of each injector. This step ensures that the injectors are receiving the necessary power to function correctly. By following these steps and comparing your measurements to the expected values, you can identify any issues with the injectors' resistance, helping to pinpoint potential problems and ensure proper functionality.
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Frequently asked questions
A resistor box is a simple device that steps down the current between the ECU and fuel injectors.
For OBD-I vehicles, locate the driver-side harness connectors near the brake master cylinder. Using a multimeter, locate the four wires that go to the injectors. Cut these four wires and connect the injector-side wires to the resistor box's black wires.
Use a multimeter to check for 12 volts on the red power wire of each injector.
Peak and hold (low impedance) injector coils exhibit less electrical resistance than saturated (high impedance) injector coils.
