Fuel Flex Sensor Placement: Settling the Debate – Part 2: Advanced Considerations and Best Practices
In Part 1 of this discussion, we established the fundamental importance of fuel flex sensors in unlocking the performance potential of E85 by accurately measuring ethanol content and relaying this crucial information to the ECU. We also addressed the core principles of optimal sensor placement in both return-style and deadhead (with a return) fuel systems, emphasizing the critical need to position the sensor in the supply line, before the fuel rail, to minimize lag.
In this second part, we delve deeper into advanced considerations and best practices for fuel flex sensor installation, tuning, and mitigating potential limitations to ensure accurate and reliable operation.
Expanding on Best Practices:
Beyond simply placing the sensor in the correct location, several best practices can further optimize the performance and reliability of your flex-fuel system:
Installation:
* Orientation: While not always critical, orienting the sensor vertically with the electrical connector facing upwards can help prevent air pockets from accumulating within the sensor body. Always refer to the manufacturer’s recommendations for specific orientation guidelines.
* Secure Mounting: Ensure the sensor is securely mounted to prevent vibrations, which could potentially affect readings over time.
* Wiring: Use high-quality wiring such as mil-spec and ensure a secure and reliable connection to the ECU. Shielded wiring may be necessary in some environments to minimize electrical interference.
Tuning:
* Professional Expertise: As mentioned previously, tuning a flex-fuel system is a complex process best left to experienced professionals with access to a dynamometer and wideband oxygen sensor.
* Comprehensive Mapping: Ensure the tuner meticulously maps the ECU’s fuel and ignition timing tables across the entire spectrum of ethanol percentages your application might encounter. This includes accounting for various load and RPM points.
* Stoichiometric AFR Calibration: Verify that the ECU is correctly programmed with the stoichiometric air-fuel ratio (AFR) for different ethanol blends. This is crucial for accurate closed-loop fueling.
Mitigating Flow Restrictions:
* Bypass Adapter Selection: When using bypass adapters in high-flow applications, choose a size and design appropriate for your fuel system’s flow rate. Ensure the adapter allows for sufficient fuel sampling by the sensor while maintaining adequate flow to the engine.
* High-Flow Sensor Options: Investigate if higher-flowing fuel flex sensor designs are available that might minimize the need for a bypass adapter in moderately high-flow systems.
* Component Matching: Ensure all fuel system components, including the fuel pump, lines, and regulator, are adequately sized to meet the demands of your application, especially when running E85, which requires approximately 25%-30% more fuel volume than gasoline for the same power output.
The Complexity of Flex-Fuel Tuning:
It’s important to reiterate that flex-fuel tuning goes beyond simply adjusting fuel and timing at a single ethanol percentage. The ECU must seamlessly interpolate between different fuel and timing maps as the ethanol content changes. This requires a thorough understanding of engine behavior across a wide range of conditions and meticulous attention to detail during the tuning process.
Variations in Sensor Technology:
While the fundamental principle of measuring fuel conductivity remains consistent, different manufacturers may employ slightly varying sensor technologies and internal designs. Some newer sensors might offer improved accuracy, faster response times, or enhanced flow characteristics. Consulting sensor specifications and manufacturer recommendations is always advisable.
The Role of Fuel Tank Design:
As briefly mentioned in Part 1, fuel tank design can influence how effectively different fuels mix. Baffled fuel tanks, for instance, are designed to minimize fuel sloshing but might also create localized areas with slightly different ethanol concentrations immediately after refueling. While a well-placed sensor in the supply line will eventually read the blended fuel, understanding this potential temporary variation is helpful.
Examples of Bypass Adapters:
Common types of bypass adapters include simple T-fittings with a restricted internal diameter in the sensor port or more sophisticated billet aluminum housings with integrated bypass channels designed for specific flow rates. The choice of adapter will depend on the sensor design and the specific demands of the fuel system.
Quantifying Flow Restriction:
While the exact flow restriction will vary depending on the specific fuel flex sensor design, many common sensors with narrow internal diameters can introduce a significant restriction in high-flow applications. For example, some sensors might restrict flow by 10-20% at flow rates exceeding 100-150 liters per hour. This restriction can become a bottleneck in high-horsepower builds, necessitating the use of a bypass adapter.
Considering Specific Fuel System Configurations:
While the general recommendations hold true for most common return-style and deadhead (with a return) fuel systems, very specific or unconventional configurations might require careful consideration. For example, in staged injection systems where multiple sets of injectors are activated at different load levels, the optimal sensor placement might need to be evaluated based on which set of injectors is primarily active during different operating conditions.
Understanding Temperature Sensitivity:
Fuel conductivity, and therefore the sensor’s output, can be slightly affected by fuel temperature. While modern ECUs often incorporate temperature compensation strategies, extreme temperature variations could potentially lead to minor inaccuracies in the ethanol reading. Proper sensor placement away from direct heat sources can help mitigate this.
Conclusion: Optimizing Your Flex-Fuel System
By understanding the core principles of fuel flex sensor operation and adhering to best practices for installation and tuning, you can maximize the benefits of E85 and ensure your engine operates safely and efficiently across a wide range of ethanol blends. While the debate surrounding sensor placement has often led to confusion, the evidence clearly points to positioning the sensor in the supply line, before the fuel rail, as the optimal solution for both return-style and deadhead (with a return) fuel systems. In high-flow applications, the use of bypass adapters is crucial to prevent fuel flow restrictions. As flex-fuel technology continues to evolve, a thorough understanding of these principles will remain essential for enthusiasts and professionals seeking to harness the full potential of ethanol-based fuels.
Written by Julian Austin – CEO & Founder (Aftermarket Industries)