Mercedes Mullins
Testing the deadtimes for a fuel injector involves measuring the time it takes for the injector to open and close, known as the injector lag time. This process can be done using various methods and tools, such as the dribble test, AEMLog, or Microsoft Excel. By running tests at different voltages and pulse widths and measuring the amount of fuel delivered, you can calculate the injector dead time. The dead time values can vary depending on the type of injector and the operating conditions, such as voltage and fuel pressure. It's important to note that the term dead time may not accurately reflect the complexity of the variable in real-life applications.
Characteristics and Values of Testing Deadtimes for a Fuel Injector
| Characteristics | Values |
|---|---|
| Injector Dead Time | 1.19ms, 1.15ms, 1.2ms, 930us, 1.708ms, 12,000 events @ 6ms, 24,000 events @ 3ms |
| Injector Open Time | 1.0ms |
| Voltage | 13.7V, 13.4V, 13.6V, 11V, 14.5V, 15 amps |
| Fuel Pressure | 60psi |
| Fuel Output | 10ml, 5-6ml |
| Injector Pulse Width | 3ms, 6ms, 2000 x 5mS bursts |
| Injector Size | 750cc, 365cc |
| Injector Type | Altezza injectors, high-impedance injectors |
| Injector Lag Time | OT, CT |
| Correction Factor | X * 0.032 |
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What You'll Learn
Injector lag time is the time taken to open and close
Injector lag time, or "dead time", is the time taken for an injector to open and close. This is the time from when the injector is energised until it is fully open, and then the time it takes to close again. It is important to get an accurate measurement of this time to ensure a stable and accurate idle, and accurate AFRs while engine braking.
There are a few different methods for testing injector dead time. One method involves idling the car while data logging and changing the injector electrical pulse width slowly up and down while logging. The car must have a stable idle at a fixed RPM, and the battery voltage must remain constant. By logging the MAP, AFR, battery volts, and injector electrical pulse width, you can then slowly raise and lower the injector on time until the RPM drops or the car misfires. This will give you an accurate measurement of the injector dead time.
Another method is the "dribble test", where you run the injector at a voltage and pressure to spec, and then increase the pulse width until you get repeatable amounts, usually 10ml for current-gen injectors. You can also do the same test with a scope hooked up to watch a wide range of the pulse, which will show you when the coil starts to become stable.
The time it takes for an injector to open and close can vary depending on the manufacturer and the specific injector. Some injectors may have faster response times than others, and it is important to get an accurate measurement to ensure the engine is running efficiently.
Injector lag time is an important factor in engine performance and fuel efficiency, and accurate measurement and calibration can help ensure optimal performance.
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Dead time changes with voltage at the injector
Injector dead time refers to the time between the activation of a fuel injector and the moment fuel starts flowing. Injector dead time is influenced by the voltage at the injector, and this relationship is not linear. As the voltage changes, the dead time can vary significantly, and this can affect the overall performance of the engine.
In the case of a 12p voltage setup, the voltage offset is the dead time table. For example, in double fire mode, the commanded injector pulse width is calculated as the dead time plus the base pulse width (BPW). So, if the dead time is 2ms and the BPW is 3ms, the injector pulse width in double fire mode is 5ms. However, in single fire mode, the commanded injector pulse width is calculated as the dead time plus twice the BPW. Therefore, using the same values, the injector pulse width in single fire mode would be 8ms.
The impact of voltage on dead time can be observed when comparing the commanded injector pulse width to the actual fuel delivered. For instance, if the dead time is 2ms, the double fire mode will result in a 4ms injector pulse width, while single fire mode will result in a 7ms injector pulse width. This variation in dead time can lead to significant differences in the amount of fuel delivered, which can affect the air-fuel ratio (AFR) and engine performance.
To compensate for these variations in dead time with voltage changes, some engines use a voltage offset table. This table ensures that despite voltage differences, the flow amount remains constant. By referring to this table, the injector coil can adjust its operation to maintain a consistent fuel delivery rate across the voltage range.
Additionally, it is important to note that larger injectors with slower dead times may struggle to idle stoichiometrically. This is because they cannot be cycled fast enough to maintain a stable air-fuel mixture. As a result, accurate dead-time numbers are crucial for larger injectors to ensure proper fuel delivery and engine performance.
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Use AEMLog or Excel to calculate dead time
To calculate the dead time of a fuel injector, you can use AEMLog or Microsoft Excel.
Using AEMLog
Firstly, idle your car while datalogging. You should have a means of changing the injector electrical pulse width slowly up and down while logging. Ensure that your car has a reasonably stable idle at a fairly fixed RPM, and battery voltage must remain constant throughout. Log the MAP, AFR, battery volts, and injector electrical pulse width while idling. Slowly raise and lower the injector on time until the RPM starts to drop significantly or the car starts to misfire. Repeat this process several times. Then, examine the datalogs. Do an XY plot, with the MAP divider AFR on the X-axis and the injector on-time on the Y-axis.
Using Excel
The process for using Excel is very similar to the process for AEMLog. After you have examined the datalogs, open Microsoft Excel. Do a scatter plot, then add a trendline. Select "linear", and in the options, select "show equation". If your data is clean and has little noise, the Y-intercept will show in the equation. If not, select "Set Intercept", and try different values until the trendline appears to describe the quiet part of the data. The datapoints should form a line. If you project this line to the Y-axis, the intercept is the dead time.
Other Testing Methods
There are several other methods for testing fuel injector dead times. One method is the dribble test, where you run at a voltage, run pressure to spec, then increase the pulse width until you get repeatable amounts. Another method is to do the same but with a scope hooked up, and watch a wide range of the pulse—you'll see when the coil starts to become stable.
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The dribble test: run at a voltage, run pressure to spec, then increase pulse width
The dribble test is one of the easiest methods to test deadtimes for a fuel injector. It involves running the injector at a specific voltage and pressure, and then gradually increasing the pulse width to achieve repeatable amounts of fuel injection. The goal is to achieve stability, with most current-generation injectors being able to maintain stability at around 5-6ml, while some can go as low as 10ml.
To perform the dribble test, start by setting up the injector at a constant voltage. The voltage plays a significant role in injector dead time, as higher voltages result in shorter dead times and vice versa. By adjusting the voltage, you can fine-tune the injector's performance. Ensure that the pressure is also set according to the specifications provided by the manufacturer.
Once the voltage and pressure are stable, you can begin adjusting the pulse width. The pulse width determines the duration of the fuel injection. Start with a relatively low pulse width and gradually increase it in small increments. With each increase in pulse width, the injector will deliver a greater amount of fuel.
As you increase the pulse width, pay close attention to the amount of fuel being injected. The dribble test aims to find the point at which the injector delivers a repeatable amount of fuel with each pulse. This means that the amount of fuel injected remains consistent across multiple pulses at the same pulse width.
For example, let's say you start with a pulse width of 5ml. You might find that the injector delivers varying amounts of fuel with each pulse, such as 9.8ml, 10.2ml, 9.9ml, etc. As you gradually increase the pulse width to, let's say, 10ml, you should eventually reach a point where the injector consistently delivers 10ml of fuel with each pulse. This repeatable amount indicates that the injector is performing within the desired specifications.
The dribble test is a straightforward method to dial in the deadtimes of fuel injectors. By adjusting the voltage, pressure, and pulse width, you can optimise the injector's performance and ensure accurate fuel delivery. This process is crucial for maintaining the efficiency and stability of the engine.
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Using a Link G4+ and injector test bench to calculate dead time
To calculate the dead time of a fuel injector using a Link G4+ and an injector test bench, you can follow these steps:
Firstly, it is important to understand that dead time refers to the time it takes for a fuel injector to open and close. This time interval can affect the amount of fuel delivered to the engine, and thus, it is crucial to accurately measure and set the dead time to ensure optimal engine performance.
Before beginning the test, ensure that you have the necessary equipment, including the Link G4+, a standard fuel rail with a variable FPR, and a netbook to run the Link G4+. Additionally, it is recommended to have a graduated cylinder to measure the amount of fuel dispensed during the test.
The first step is to use the "Advanced Injector Test" function on the Link G4+ to run a series of tests at a single voltage, such as 13.4V, with varying pulse widths. For example, you can run 12,000 events at 6ms and then 24,000 events at 3ms. By observing the amount of fuel dispensed into the graduated cylinder during each test, you can identify any deviations from the expected linear flow rate, which indicate the presence of dead time.
After collecting the test data, you can use a spreadsheet program such as Microsoft Excel to analyze the results. Create a scatter plot of the data and add a trendline with the "Exponential" type selected. The y-intercept of this trendline will provide an approximation of the dead time. Fine-tune this approximation by adjusting the dead time number up or down until the line on the graph becomes horizontal, indicating a linear relationship between pulse width and fuel dispensed.
It is worth noting that the Link G4+ offers advantages over the Link G4, including the availability of a minimum pulse width setting and a short pulse width adder table, which can streamline the testing process and provide more accurate results. Additionally, ensure that you test across a range of voltages to account for the fact that injector dead time can vary significantly with voltage.
By following these steps and analyzing the test results, you can accurately calculate the dead time of a fuel injector using a Link G4+ and an injector test bench. This information can then be used to fine-tune the injector settings for optimal engine performance.
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Frequently asked questions
Injector “deadtime” is the time it takes for an injector to open (open time) from the time it has been energized until it is fully open.
One way to test for fuel injector deadtime is to use the "Advanced injector test" function, which involves firing some fuel into a graduated cylinder to measure the results. The first test is to find out the deadtime at one voltage only, so you would run a series of tests at varying pulse widths.
Another method is the dribble test, where you run at a voltage, run pressure to spec, then increase the pulse width until you get repeatable amounts. You can also do the same thing with a scope hooked up to watch a wide range of the pulse, and you'll see when the coil starts to become stable.
