Team Harley ECU 2010

Project Definition


Businesses or individuals who desire a plug-N-play customizable engine controller.

The Problem

Customers want to customize their bikes.

Doing so with the stock ECU presents risks:
  • Reduced fuel efficiency
  • Reduced engine life
  • The Solution

    Design a module that serves as a plug-N-play interface between the Harley-Davidson and the MicroSquirt EFI Controller.

  • Use the MicroSquirt for configurable engine control
  • Receive real-time data from the MicroSquirt using RS-232
  • Generate J1850 messages to communicate with the gauges on newer bikes (2004-present)
  • Generate variable frequency square waves to communicate with gauges on older bikes (before 2004)
  • Specifications

  • Entire unit must fit inside the stock ECU container
  • Communicate MPH and RPM data on bike's J1850 network
  • Process real-time data from MicroSquirt's RS-232 bus
  • Detect a PC connection and disable RS-232 transmitters on the interface (Sniffing Mode)
  • Provide protected power to the controller module and interface
  • The Microsquirt

    The MicroSquirt is a customizable engine control unit that features:
  • Freely available code
  • Community support
  • Extensive documentation
  • User configurability
  • RS-232 communication support
  • Compact size
  • Designed to be “plugged in” to other projects
  • A relatively low price ($249)
  • Megatune

    Megatune is the tuning software used to configure the MicroSquirt.

    Features include:
  • Freely-available code
  • Support documentation
  • Data logging capabilities
  • Real-time display to help in tuning
  • Calibration wizards to aid in tuning
  • The Interface Board


  • Receives and routes sensor input to MicroSquirt
  • Sends RS-232 data requests to the MicroSquirt
  • Translates RS-232 data for RPM and MPH gauge control (via J1850 network for newer bikes and a PWM signal for older bikes)
  • Detects PC connection and manages transition to Sniffer Mode for tuning
  • Manages RS-232 transmitter operations to avoid conflicts during tuning
  • Performs idle air control


  • Microcontroller: Atmel ATMEGA48
  • Communication: Freescale MC33390 J1850 transceiver, Maxim MAX3221 RS-232 transceiver
  • Connectivity: 36-pin Delphi Connector for interfacing with the bike

    Interface Board Connectors

    Microcontroller & Transceivers

    Power Supply

    Ignition Drivers / Fuel Pump Relay

    Interface Board Layout

  • Flow Diagram

  • Flow Diagram