Fuel Injector Electrical Resistance: Temperature Sensitivity Explored

Fuel injectors are a type of solenoid that delivers precise amounts of fuel into the cylinder. Over time, fuel injectors can wear out or become clogged, preventing the engine from operating correctly. The fuel injector is an electro-mechanical device, so both electrical and mechanical failure modes are possible. One of the most common types of fuel injector failure is contamination and internal o-ring failure. The electrical resistance of fuel injectors can be measured using a digital volt-ohmmeter (DVOM) or a multimeter with ohms setting. High impedance injectors, which are the most common type found in modern cars, typically have a resistance ranging from 12 to 17 ohms. On the other hand, low impedance injectors, which are found in high-performance and larger injectors, have a much lower resistance, typically around 2-5 ohms. It is important to ensure that fuel injectors receive the correct voltage and have the correct resistance to function properly and maintain fuel efficiency. While temperature does not seem to be a significant factor in injector resistance, it is worth noting that fuel temperature can impact the flow rate of some injectors, such as the Bosch 1600 EV14.

Injector flow and temperature

The relationship between injector flow and temperature is complex and depends on various factors, including the type of fuel, injector design, and driving conditions. For example, the effect of temperature on fuel density is more significant for gaseous fuels than for liquid fossil fuels. Additionally, the impact of temperature on injector flow may be more noticeable at very low duty cycles.

It's worth noting that while modern fuel injectors are generally less sensitive to temperature changes, older injectors or those with design flaws may exhibit more significant variations in fuel delivery at different temperatures.

To compensate for the effects of temperature on injector flow, some vehicles use a return fuel line to circulate cooler fuel and help maintain lower temperatures. Additionally, fuel temperature sensors can be used to monitor the fuel temperature and adjust the injector settings accordingly. However, fuel temperature sensors are not commonly used by original equipment manufacturers (OEMs).

Fuel injector failure

Fuel injectors are an electro-mechanical device, so both electrical and mechanical failure modes are possible. One of the most common types of fuel injector failure is contamination and restriction. All the fuel the engine burns passes through the injectors, making them susceptible to contamination and carbon build-up, which eventually restricts the flow of fuel. This can be caused by fuel quality, driving conditions, and injector design. Restricted injectors can cause a reduction in fuel flow, resulting in high emissions, poor fuel economy, and poor performance. They can also affect the spray pattern, leading to poor atomization of the fuel.

Another common issue is internal o-ring failure, where the o-rings that keep fuel from leaking out of the injector fail, causing external leaks. This can result in fuel odor and seepage, especially under certain temperatures or driving conditions.

Diagnosing fuel injector failure can be challenging, and it is important to rule out other potential causes, such as ignition-related issues or mechanical failures. Some common symptoms of fuel injector failure include:

• Engine misfires
• Rough idling
• Poor fuel economy
• Unpredictable RPM needle movement
• Engine failure to start
• Check engine light illuminated
• Fuel leaks

Injector temperature and air/fuel ratio

Injector temperature can affect the air/fuel ratio, which is the ratio of air to fuel in the combustion process. An ideal air-fuel ratio results in complete combustion and maximum power output.

The temperature of the injectors can influence the electrical resistance, which in turn affects the fuel flow. For example, the Bosch 1600 EV14 injector is known to have a significant impact on the air/fuel ratio as the fuel temperature changes. However, modern injectors, such as the Bosch injectors, seem to be less affected by temperature variations.

The inlet air temperature also plays a crucial role in the performance and emission behaviour of homogeneous charge compression ignition engines (HCCI). Increasing the inlet air temperature can improve the vaporisation of diesel fuel but may also lead to higher knocking intensity, higher NOx emissions, and misfires. Therefore, finding the optimal inlet air temperature is essential for efficient engine operation.

Additionally, the fuel injection pressure can impact the performance and emissions of HCCI engines. Higher injection pressure can enhance engine performance and reduce NOx and smoke emissions. However, it is important to monitor and control the injection pressure to prevent high levels of HC and NOx emissions.

To achieve optimal engine performance and fuel efficiency, it is crucial to maintain the correct air-fuel ratio by considering factors such as engine load, speed, temperature, and pressure variations.

Fuel injector cleaning

Fuel injectors are susceptible to contamination and carbon build-up, which can restrict the flow of fuel and lead to problems such as rough idling, stalling, misfires, sputtering, and poor acceleration. While fuel injector cleaning is often recommended, it may not be necessary unless it is addressing a specific issue.

There are three main methods for cleaning fuel injectors:

• Using detergents in the gasoline itself: This is the easiest and likely the least expensive method. Detergent additives in gasoline have been federally mandated, but the quantity of detergent can vary by brand. Top Tier gasolines are determined by independent testing to have two to three times as much detergent as federally required. Some manufacturers specifically recommend using Top Tier gasoline.
• Adding bottles of fuel injector cleaner to the gas tank: Some manufacturers suggest using a fuel injector cleaning additive if you don't always use Top Tier gas. These additives, typically priced between $5 to $15 per bottle, are poured into the tank before filling it with gasoline so that they can mix thoroughly. However, there is no independent testing entity that rates these additives, and using them in older engines or those not running well could potentially cause issues by dislodging built-up debris.
• Professional cleaning: This option involves mechanics forcing cleaners under pressure through the fuel injectors, either while they are still on the engine or after removal. The cost of this procedure varies, but it is generally more expensive than using Top Tier gas or bottled additives.

It is important to note that regular fuel injector cleaning as a preventive measure is typically not mentioned in manufacturers' maintenance schedules. Additionally, there is no one-size-fits-all answer to whether or not fuel injectors need periodic cleaning, as it depends on the specific car and situation. However, using Top Tier gasoline with the occasional bottle of fuel injector cleaner should generally be sufficient to maintain clean injectors and address mild running issues.

Fuel injector wiring

Fuel injectors are electro-mechanical devices, so they can fail in both electrical and mechanical ways. Fuel injectors can be divided into two main groups: high impedance and low impedance. High-impedance injectors are the most common type and the simplest to wire and configure. They have two terminals, one of which is supplied with 12 volts from the power supply system when the engine enable switch is on or the key is in the "on" position. The other pin is wired to a dedicated injector output channel of your ECU. It doesn't matter which pin you use on the injector as they are not polarity-sensitive.

To open a high-impedance injector, the ECU provides a ground connection, allowing current to flow from the power supply system, through the injector, through the ECU, and to ground. The amount of current that will flow is limited by the injector's impedance. This simple switching strategy is known as saturated drive, a term often seen in ECU documentation.

Low-impedance injectors are wired in the same way as high-impedance injectors but are controlled by the ECU in a more complicated way. If the ECU simply provided a ground connection for the injector and allowed the current to flow unrestricted, the low impedance would not limit the current sufficiently, leading to potential damage to the ECU or the injector. To control a low-impedance injector correctly, the ECU will initially allow a large current to pass to open the injector quickly and then limit the current to a lower level for the rest of the injection period.

You can determine whether your injectors are low or high impedance by measuring the resistance across the two terminals with a multimeter. Low-impedance injectors typically read 2.5 to 3 ohms, while high-impedance injectors give a reading of around 12 ohms. It is possible to run a low-impedance injector from a saturated injector drive by adding some resistance to the injector circuit through ballasting. This is frequently seen on OEM vehicles, such as the RB26 fitted to the Nissan GT-R.

When checking the resistance of fuel injectors, you can identify a weak injector (resistance too low) or one with an open circuit (infinite resistance). Additionally, a resistance check can indicate a leaking fuel system by monitoring the leak-down rate. While resistance measurements can reveal gross failures in the coil, they may not detect a short to the adjacent turn, which can affect performance. A more conclusive test is to measure the inductance and coil "Q" with an impedance bridge.

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