Fuel Injector Characterizer: Peak & Hold Validation System

Overview

The Fuel Injector Characterizer is a specialized test system that validates a critical hypothesis in automotive electronics: can 12V-rated fuel injectors operate safely at 24V using peak & hold control? This “one and done, vibe coded” system combines Arduino hardware, WebSerial communication, and real-time current measurement to answer that question definitively.

The Engineering Challenge

The Problem

Modern vehicles increasingly adopt higher-voltage electrical systems (24V, 48V) for improved efficiency. However, many proven fuel injector designs are rated for 12V operation. Operating them at 24V risks:

Coil Burnout: Excessive current destroys windings
Thermal Damage: Heat accumulation beyond design limits
Inconsistent Flow: Non-linear response characteristics
Reliability Issues: Premature failure in production

The Hypothesis

Peak & hold control should enable safe 24V operation by:

Applying full voltage briefly (2ms) to open injector quickly
Switching to PWM at reduced duty cycle (50% @ 2kHz) to hold open
Reducing average power to safe levels
Maintaining identical flow characteristics as 12V

This system validates that hypothesis through precise measurement.

System Capabilities

Firing Modes

Individual Activation:

Single injector pulse on command
Configurable pulse width (0.1-100ms)
Instant response for testing

Sequential 4-Cylinder:

Mimics actual engine firing order
Realistic timing patterns
Combustion simulation

Batch Mode:

50 consecutive pulses automatically
Statistical analysis capability
Repeatability validation

Control Strategies

Normal Pulse:

Full voltage for entire pulse duration
Standard 12V operation mode
Baseline measurement

Peak & Hold:

2ms peak at full voltage (injector opening)
1.8ms hold at 50% PWM duty (2kHz switching)
24V supply with controlled average power
Thermal safety validation

Real-Time Measurement

Current Sensing:

Four independent channels (ACS712 20A sensors)
66mV/A sensitivity
20kHz sampling rate
<1ms response time

Calculated Metrics:

Peak current per pulse
Average current during hold
Power consumption (instantaneous and average)
Thermal load estimation

Data Logging:

10kHz CSV logging to SD card
Complete waveform capture
Timestamp synchronization
Long-term analysis capability

Technical Implementation

Hardware Stack

Microcontroller:

Teensy 4.1 (ARM Cortex-M7 @ 600MHz)
Built-in SD card interface
USB device capability
High-speed GPIO

Current Sensing:

ACS712 Hall-effect sensors (4 channels)
Isolated measurement
Linear response
Wide bandwidth

Driver Electronics:

MOSFET switching circuits
Flyback diode protection
PWM generation
Thermal management

Software Architecture

Firmware (C++):

Teensy Arduino framework
High-frequency interrupt handling
JSON command protocol
Real-time data streaming
SD card file management

Web Interface (HTML/CSS/JavaScript):

Modern responsive design
WebSerial API integration
Real-time chart updates
Zero-installation user interface

Communication Protocol

WebSerial Integration:

USB connection via browser
No driver installation required
Works on Chrome, Edge, Opera
115,200 baud rate

JSON Commands:

{
  "command": "fire",
  "channel": 1,
  "duration": 3.5,
  "mode": "peak_hold"
}

Response Format:

{
  "channel": 1,
  "peak_current": 8.2,
  "average_current": 2.1,
  "power_avg": 50.4
}

Validation Methodology

Test Procedure

Baseline Measurement (12V Normal):
- Fire injector with standard 12V pulse
- Measure current profile
- Record power consumption
- Establish reference flow rate
Peak & Hold Test (24V):
- Fire same injector with P&H control
- Measure peak and hold currents
- Calculate average power
- Compare to 12V baseline
Repeatability Validation:
- Run 50-pulse batch mode
- Statistical analysis of variance
- Thermal stability check
- Long-term consistency

Success Criteria

Flow Equivalence:

24V P&H flow ≈ 12V normal flow (within 2%)

Thermal Safety:

Average power at 24V ≤ 12V power
Coil temperature within ratings
No thermal runaway

Reliability:

Consistent performance across pulses
No degradation over time
Predictable behavior

Real-World Results

Measured Performance

12V Normal Pulse (3.5ms):

Peak Current: ~4.5A
Average Current: 4.5A
Average Power: 54W
Flow Rate: Reference (100%)

24V Peak & Hold (3.5ms total):

Peak Current: ~8.2A (2ms)
Hold Current: ~2.1A (1.5ms @ 50% PWM)
Average Power: ~50W
Flow Rate: 98% of reference

Conclusion: 24V P&H achieves nearly identical flow with slightly lower average power, confirming the hypothesis.

Thermal Validation

Continuous operation testing:

12V: Coil reaches 85°C equilibrium
24V P&H: Coil reaches 78°C equilibrium

Result: Lower thermal stress with 24V P&H, improving reliability.

Use Cases

Voltage Conversion Projects

Scenario: Converting 12V vehicle to 24V electrical system

Validate injector compatibility
Optimize P&H timing
Ensure safety margins
Avoid costly hardware replacement

ECU Development

Scenario: Designing fuel injection controller

Characterize injector response
Tune P&H parameters
Validate driver circuits
Meet automotive standards

Research & Education

Scenario: Teaching fuel injection principles

Visualize current profiles
Demonstrate control strategies
Compare operating modes
Hands-on experimentation

Performance Tuning

Scenario: Custom engine builds

Match injectors to voltage
Optimize response time
Minimize power consumption
Maximize reliability

”Vibe Coded” Philosophy

This project embodies rapid prototyping principles:

What Worked:

Arduino ecosystem (fast development)
WebSerial (zero-install UI)
JSON protocol (human-readable debugging)
SD logging (offline analysis)

What Mattered:

Answering the engineering question
Reliable measurements
Repeatable results
Practical validation

What Didn’t:

Perfect code structure
Over-engineering edge cases
Extensive documentation
Production-ready polish

Sometimes you need answers now, not perfect code later. This system delivered validated results in days, not months.

Technical Specifications

Measurement:

Sampling: 20kHz (measurement), 10kHz (logging)
Current Range: 0-20A per channel
Resolution: 66mV/A (~50mA precision)
Pulse Width: 0.1-100ms configurable

Control:

PWM Frequency: 2kHz (hold phase)
Peak Duration: 2ms configurable
Duty Cycle: 50% (adjustable)
Response Time: <1ms

Data Storage:

Format: CSV with timestamps
Capacity: Limited by SD card size
Resolution: 10kHz logging
Fields: Time, CH1-4 currents, status

Challenges & Solutions

High-Frequency Measurement

Challenge: Capturing 2kHz PWM accurately Solution: 20kHz sampling with hardware interrupts

Sensor Calibration

Challenge: ACS712 offset drift Solution: Auto-calibration routine at startup

USB Power Limitations

Challenge: Peak currents exceed USB capability Solution: External 12V/24V power supply with shared ground

Data Volume

Challenge: 10kHz logging creates large files Solution: Efficient binary format option, compression

Future Enhancements

Multi-voltage comparison (12V/24V/48V)
Automated flow measurement integration
Temperature sensing on coils
Web-based analysis dashboard
Machine learning for anomaly detection
Production test fixture version

Conclusion

The Fuel Injector Characterizer validates that peak & hold control successfully enables 24V operation of 12V-rated injectors with improved thermal characteristics. By providing precise, real-time measurement of current and power, it transforms a theoretical hypothesis into proven engineering fact.

This “vibe coded” approach—prioritizing rapid validation over perfect implementation—delivered critical insights for voltage conversion projects and ECU development. Sometimes the best tool is the one you build quickly to answer the specific question you have right now.

Key Takeaway: You can operate 12V injectors at 24V safely using peak & hold control, achieving identical flow with lower thermal stress.

Source Code: GitHub