Sylvie Willis
Fuel injector dead time is the time it takes for a fuel injector to fully open. This is also referred to as injector latency or lag time. The amount of time it takes for a fuel injector to fully open depends on several factors, including the size of the injector, the viscosity of the fuel, the manifold pressure, and the fuel pressure. Big injectors need accurate dead-time numbers because the flow is dependent on the difference between two large numbers. It is critical to have accurate injector dead time settings for a quality idle and to maintain air/fuel ratios when there are accessory loads on the engine, such as headlights or a heater.
| Characteristics | Values |
|---|---|
| Definition | Injector "dead time" is the time it takes for an injector to open from the time it has been energized until it is fully open. |
| Alternative names | Injector lag time, latency, delay |
| Factors affecting injector dead time | Size of fuel injectors, viscosity of fuel, manifold pressure, fuel pressure, battery voltage, injector temperature |
| Importance | Critical for a quality idle and maintaining air/fuel ratios when there are accessory loads on the engine |
| Sources of dead time values | Injector supplier or manufacturer, tuning software, engine management systems |
| Fine-tuning methods | Adjusting voltage, fuel pressure levels, fuel trim values, intake calibration tables, injector size |
| Common issues | Inaccurate dead-time numbers, engine running too rich or too lean, strange driveability problems |
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What You'll Learn
- Injector lag time is the time taken for an injector to open fully
- Dead-time numbers are critical for quality idling and maintaining air/fuel ratios
- Injector latency is dependent on factors like injector size, fuel viscosity, and pressure
- Dead-time varies with injector temperature, especially with high-impedance injectors
- Dead-time values can be calculated and fine-tuned using engine idle and fuel trim data
Injector lag time is the time taken for an injector to open fully
Injector lag time, also known as injector dead time, is the time taken for an injector to open fully from the point it is energised. This time is critical for a quality engine idle and maintaining air-fuel ratios when accessory loads are applied to the engine, such as headlights or heaters.
The time taken for an injector to open fully can vary depending on several factors. These include the size of the injector, the viscosity of the fuel, manifold pressure, and fuel pressure. For example, larger injectors will require a longer electrical pulse width to deliver the same amount of fuel as smaller injectors. Therefore, if the dead time is set too low, the injector will deliver too much fuel, and if it is set too high, it will not deliver enough.
The battery voltage also has an impact on injector lag time. Lower voltages require increased injector latency, which means the injector will open sooner, resulting in a greater total fuel delivery. Conversely, higher voltages may decrease injector latency, causing the injector to open later and deliver less fuel. The injector temperature can also affect the dead time, as higher temperatures will generally result in a shorter dead time.
It is important to have accurate injector dead time values when installing aftermarket injectors. If these values are incorrect, the engine may run too rich or too lean, leading to strange driveability problems. To avoid this, it is recommended to first tune the MAF translation table to suit a new intake system with stock injectors, or change the injectors and then tune the scaling/latency with the stock intake.
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Dead-time numbers are critical for quality idling and maintaining air/fuel ratios
Fuel injector dead time is the time it takes for a fuel injector to fully open from the moment it is energised. This is also referred to as injector latency or lag time. The amount of time it takes depends on several factors, including the size of the injector, the viscosity of the fuel, the manifold pressure, and the fuel pressure. For example, higher fuel pressure may increase the injector's latency.
The error becomes even more significant when larger injectors are used. For example, if the injector size is tripled, the electrical pulse width required becomes 1.3 milliseconds. If the dead-time is still set incorrectly at 1.1 milliseconds, the error increases to 33%. Therefore, accurate dead-time numbers are crucial for larger injectors as the flow is dependent on the difference between two large numbers.
Additionally, dead-time can vary with battery voltage and injector temperature. For instance, a 600cc DW injector may have a dead-time of 920 microseconds when cold, but this increases to 1.05 milliseconds when warm. If the dead-time is set to 1.05 milliseconds, the warm-up will be too rich, and setting it too low will result in a lean misfire at low MAP and stalling at idle. As such, it is essential to fine-tune the dead-time numbers to ensure quality idling and maintain the correct air/fuel ratios.
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Injector latency is dependent on factors like injector size, fuel viscosity, and pressure
Injector latency, or "dead time", is the time it takes for a fuel injector to start spraying fuel after receiving a signal to do so. This time is dependent on several factors, including the size of the injector, the viscosity of the fuel, and the pressure.
Injector size plays a crucial role in determining the latency of a fuel injector. Larger injectors with higher flow rates will generally have longer latency periods. This is because they require more time to build up the necessary pressure to start spraying fuel. Conversely, smaller injectors with lower flow rates will typically have shorter dead times due to their reduced internal volume and faster pressure buildup.
Fuel viscosity, or thickness, is another factor that influences injector latency. Higher viscosity fuels tend to increase the dead time of fuel injectors. This is because thicker fuels flow more slowly and take longer to pass through the injector, delaying the time it takes for the injector to start spraying fuel. On the other hand, lower viscosity fuels promote shorter dead times as they flow more easily and rapidly through the injector.
Fuel pressure also has a significant impact on injector latency. Higher fuel pressure can increase the injector's latency, causing a delay in the time it takes for the injector to start spraying fuel. This is because the injector needs to build up sufficient pressure to overcome the existing fuel pressure and initiate the spraying process. Conversely, lower fuel pressure can lead to reduced injector latency, resulting in quicker fuel injection.
It is important to note that while these factors play a significant role in determining injector latency, other variables, such as battery voltage, can also influence the dead time. Additionally, the specific design and characteristics of each fuel injector can result in unique latency behaviours. Therefore, it is always advisable to refer to the manufacturer's specifications and conduct careful testing to accurately determine the injector's latency for a particular setup.
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Dead-time varies with injector temperature, especially with high-impedance injectors
Injector dead time, or latency, is the time delay between the initiation of a process and the occurrence of its first noticeable effect. In the case of fuel injectors, it is the time it takes for an injector to open from the time it has been energised until it is fully open. This delay is known as opening injector latency.
Dead time varies with changes in injector temperature, especially in the case of high-impedance injectors. For example, a 600cc DW injector goes from 920 microseconds when cold to 1.05 milliseconds when warm. If the dead time is set to 1.05 milliseconds, the warm-up will be too fuel-rich. If it is set too low, the injector will get a lean misfire at low MAP and stall at idle.
The impact of dead time is more significant at idle and low speed (when small injector openings are used) and has a minimal effect at high speed and high load conditions. Dead time is also affected by factors such as the size of the fuel injectors, viscosity of fuel, manifold pressure, and fuel pressure. Lower battery voltage and higher fuel pressure both require increased injector latency (dead time).
To fine-tune the injector scale value, it is recommended to install the stock intake system and run with stock-level fuel pressure levels. With the engine idling at full temperature (coolant temperature between 180-195 degrees Fahrenheit and intake air temperature within 15 degrees Fahrenheit of ambient temperature), adjustments can be made to the scale value until the A/F Trim Mimed and A/F Learned are as close to zero as possible. +/- 5% is generally considered acceptable.
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Dead-time values can be calculated and fine-tuned using engine idle and fuel trim data
Fuel injector dead time is the time it takes for a fuel injector to fully open from the point it is energised. This time is referred to in several ways, including injector lag, latency, and delay. The amount of injector dead time depends on factors such as the size of the injector, the viscosity of the fuel, and the manifold and fuel pressure.
By baselining the fuel trim data, mechanics can identify any issues with the engine's performance. For example, if the fuel trim values are high, it could indicate that the fuel pump is not performing optimally and may need to be replaced. Additionally, the MAF sensor data can be analysed to determine the airflow in all operating ranges. This can help identify any issues with the MAF sensor, such as dirt or damage, which may cause the sensor to underestimate or overestimate the airflow, impacting the engine's performance.
When fine-tuning dead-time values, it is important to ensure that the engine is idling at full temperature, with the coolant temperature between 180-195 F and the intake air temperature within 15 degrees F of the ambient temperature. Adjustments can then be made to the scale value until the A/F Trim Mimed and + A/F Learned are as close to zero as possible, with +/- 5% generally being acceptable.
It is worth noting that dead-time values can vary with injector temperature and battery voltage. Therefore, it is crucial to have accurate dead-time numbers, especially for larger injectors, as the flow is dependent on the difference between two large numbers. Incorrect dead-time values can result in errors in fuel delivery, leading to strange driveability problems.
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Frequently asked questions
Fuel injector dead time is the time it takes for a fuel injector to fully open. It is also known as injector lag time or latency.
Having accurate injector dead time settings is critical for a quality idle and maintaining air/fuel ratios when there are accessory loads on the engine, such as headlights or a heater.
The dead time of a fuel injector can be found by consulting the manufacturer or supplier, or by using a process of trial and error.
