Injector Flow Test Bench

(In progress)

The Fuel Injector Flow Bench project was developed to provide the university’s racing team with an in-house solution for testing, cleaning, and analyzing fuel injector performance.

Objective

Modern fuel injectors demand precise control for accurate fuel delivery, but testing and cleaning them typically requires expensive, specialized equipment. To support my college’s racing team, I designed and built a low-cost, Arduino-based injector flow bench capable of testing injector performance under various pulse widths, frequencies, and duty cycles. The system also doubles as a cleaning station for clogged or contaminated injectors, providing a practical and affordable solution for both performance evaluation and maintenance.

Requirements

Goals

Use an Arduino Nano (or equivalent microcontroller) for pulse generation and mode control.
Control up to four injectors independently or in sequential firing order.
Allow for user to choose frequency, pulse width, and duration.
Operate from a 12V DC automotive power source (battery or regulated supply).
Be physically compact, modular, and serviceable.
Include as many safety features as possible.

Generate stable injector pulse control with ±0.5% timing accuracy across full duty cycle range.
Maintain consistent flow rate at duty cycles from 10% to 85%.
Support sustained operation for test durations up to 60 seconds per run without overheating.
Drive injectors with peak currents safely.
Achieve repeatable flow measurements within ±2% of measured volume between runs.
Operate reliably from 11v to 13.5v input range.
- Cost less than $250 to manufacture.
- LEARN

Design Development

Initial Concept Sketches

These early sketches capture the foundational ideas for the injector flow bench’s circuit and operating logic. They illustrate the project’s transition from conceptual design to structured implementation.

This diagram outlines the non-return fuel system layout, and an initial list of key components (Arduino Nano, MOSFETs, relays, and regulators) identified during early research and used to define the wiring strategy.

This flowchart maps the planned user interface and control logic, including mode selection (manual and automatic), adjustable parameters, and test sequence flow.

CAD Designs

The injector mount and frame were designed in SolidWorks through multiple iterations to improve strength, manufacturability, and ease of assembly. Each version addressed mechanical weaknesses identified in earlier prototypes while maintaining compact dimensions and stable injector positioning for flow testing. The overall design is intentionally modular, allowing for easy storage, quick assembly, and the flexibility to add or remove future components or redesigned parts as the system evolves.

1st Iteration

The initial concept focused on establishing the overall form factor and injector spacing. While functional for visualization, this version lacked structural rigidity around the vertical supports, which had failed during testing. These weaknesses guided the next phase of redesign.

2nd Iteration

The 2nd iteration reinforced the side columns and base to reduce flexing under load. The top section was reworked to allow easier injector installation and removal, and the base was widened for better stability. Additional mounting features were added to integrate the electrical enclosure and regulator components directly onto the frame.

3rd Iteration

The third iteration introduced additional structural and functional improvements. The upper injector mount was redesigned with reinforced supports and precision alignment slots to prevent injectors from dislodging under operating pressure and to minimize lateral movement during testing. This version also incorporated the ECU electronics enclosure.

Injector Driver Box ("ECU")

The injector driver enclosure was modeled to house the Arduino controller, MOSFET board, relay, and user interface components. The design includes cutouts for the LCD display, control buttons, status LEDs, and labeling for each function. The angled front panel provides ergonomic visibility during testing, while the compact form factor keeps wiring short and organized. This enclosure serves as the system’s central control unit — effectively the “ECU” of the flow bench.

Electronics

The electronic control system is the core of the injector flow bench, providing precise pulse timing, mode selection, and system safety management. Development progressed from breadboard prototyping to a fully designed and routed PCB design in KiCad. Each stage emphasizes modularity, noise protection, and reliable switching performance under 12-volt automotive conditions.

Partial Breadboard Layout

The initial breadboard prototype was used to validate circuit logic, test MOSFET switching behavior, and confirm LCD and button interface functionality. For initial testing, LEDs were used in place of injectors to safely visualize pulse timing and verify circuit behavior. A full breadboard layout will later be connected to actual fuel injectors to confirm proper operation before finalizing and printing the PCB.

UI Start Screen

The user interface was developed around a 16×2 LCD display to provide clear feedback during testing. I may upgrade to a full touch screen design. At startup, the system initializes all safety checks and displays a welcome screen before transitioning to the main mode selection menu.

Wiring Schematic

The wiring schematic defines all connections between the Arduino controller, MOSFET drivers, relay, LCD display, and input controls. Key design features include 10 kΩ gate pulldown resistors for signal stability, flyback diodes for injector protection, and a relay-controlled main power circuit for safe operation. There are plenty of additional safety features as well (MOSFET reverse polarity protection, TVS surge protection, etc.)

PCB Design

The final PCB was designed in KiCad and optimized for clear current flow, thermal performance, and compact packaging within the ECU enclosure. Wide copper traces were used for high-current injector paths, with separate ground paths for power and logic to minimize noise interference. The design integrates connectors for four injectors, the display module, and user interface inputs, resulting in a clean, reliable electronic system ready for enclosure mounting.

Parts List

The flow bench’s electrical and control systems were built using reliable, automotive-grade components selected for durability, safety, and ease of integration. Each part was chosen to support accurate injector control, stable power delivery, and straightforward maintenance. All components were funded by my university in support of the school’s racing team, allowing the project to be developed and tested as a functional tool for future engine development and injector calibration work.

Prototyping & Fabrication

The injector flow bench frame was fabricated through multiple rapid-prototyping stages using 3D printing to evaluate form, fit, and structural integrity before committing to final materials. All prototypes were printed using PLA filament with low infill density (3-5%) to minimize print time and material waste during early testing. Each iteration was refined based on mechanical performance, assembly feedback, and injector mounting stability. For the final version, I plan to print the structure in nylon and coat it in automotive 2k clear coat for greater strength, heat resistance, and fuel resistance, depending on project budget and university funding.

1st Iteration

The first printed prototype served as a form and fit validation model, used to confirm overall proportions and injector spacing. Low infill PLA allowed for quick fabrication and fast design feedback. While the geometry matched the CAD model, the vertical supports proved too weak under minimal load, resulting in cracking during assembly. I had initially planned to hold the fuel rail up with just straps but I realized they would need a surface to rest on. These failures provided valuable insight into stress concentration areas and guided the next redesign.

2nd Iteration

The second prototype incorporated the structural lessons learned from the first print. The frame was redesigned with thicker vertical supports, an integrated top plate, and a solid base to increase rigidity. I also began integrating the electronics enclosure at this stage to verify fitment between the frame and control components. The model was printed in PLA using light infill (about 5%) to improve print time. This iteration successfully supported the fuel rail and demonstrated proper injector alignment. This iteration also introduced mounts on the back for the fuel pump and fuel pressure regulator. These mounts were design to allow for multiple different types of pumps and regulators.

3rd Iteration

For the third prototype, I introduced several key upgrades based on prior testing. A reinforced injector support plate was added, featuring two adjustable screws to accommodate different injector sizes and prevent them from dislodging under fuel pressure during operation. The top mount design was simplified to a single central strap hole, making it easier to secure the fuel rail while maintaining clear access for installation and wiring. The rear mounting sections for the fuel pressure regulator and fuel pump were also enlarged to improve stability and component spacing. Numerous other small design refinements, such as rounded edges, improved fit tolerances, and better wire routing clearances were incorporated to enhance overall usability. This iteration represented the first fully functional physical assembly, capable of holding real injectors securely under operating pressure and supporting preliminary ECU wiring integration. It serves as the foundation for the final production version, which will likely be printed in nylon for added durability and fuel resistance.

Testing & Validation

This part of the build is in progress — photos and data will be added once testing is complete.

Results & Analysis

This part of the build is in progress — photos and data will be added once testing is complete.

Potential Improvements

This part of the build is in progress — photos and data will be added once testing is complete.

Technical Skills Applied

Mechanical & Design

Component layout and mechanical design using SolidWorks for enclosure and fixture modeling.
Development of mounting systems for injectors, relays, and electronics.
Consideration of vibration isolation, heat dissipation, and serviceability in mechanical design.
Use of 3D printing for prototype and final iterations of enclosures and brackets.

Electrical & Electronics

Design and wiring of 12v DC automotive circuit with safety features.
Implementation of MOSFET switching for injector control.
Application of grounding and noise reduction techniques for stable control signals.
Implementing fail-safe logic and modular wiring layout for future expansion.

Programming

Development of Arduino-based control firmware for pulse generation.
Programming adjustable frequency, pulse width, and duration control.
Integration of LCD menu system and button navigation interface.
Implementation of safety logic (E-stop, timed auto-shutdown, delay start).

Testing & Instrumentation

Measurement of flow rates and injector performance using graduated cylinders.
Calibration and verification of duty cycle accuracy and pulse timing.
Analysis of voltage drop and thermal performance under full load conditions.

Troubleshooting

Debugging of circuits under load.
Troubleshooting MOSFET heating, relay chatter, and timing issues.

Documentation & Presentation

Creation of circuit diagrams and schematic documentation in KiCad.
Presentation of design process and results for academic or team review.

Gallery

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