Repair-It

The RYOBI™ EFI system is designed for optimal engine performance with improved fuel efficiency and lower emissions than a comparable carbureted machine. Fuel and spark functions are electronically controlled and engine operation continuously monitored during operation to maintain an ideal air/fuel ratio and best power. Electronic control is achieved through the use of a throttle body assembly, which combines electronics, sensors, and throttle body functionality into a single unit. The EFI system components connect to the throttle body assembly through the wire harness or high pressure line.

Fuel is routed from the tank to the fuel pump module. A directional fuel filter is positioned between the tank and the pump module to prevent damage or failure of the EFI components. The fuel pump module takes in fuel from the tank via gravity feeding and generates approximately 39 psi of fuel pressure to the high pressure line. This high pressure line then terminates at the fuel injector located on the throttle body assembly where it is electronically controlled.

Spark is generated by the inductive ignition coil. Charging and discharging is electronically controlled using energy from the battery to produce the spark. The ignition timing is dynamic during the operation of the engine and will vary based on operating conditions.

To allow electronic control of various functions, a crankshaft position sensor is used to monitor a pattern of teeth machined into the engine flywheel. These teeth are detected by the crankshaft position sensor and processed such that control based on angular engine events can be achieved. The pattern of teeth are all equally spaced with a single tooth removed to provide a reference point in the rotation.

Sensor data is essential to controlling the air/fuel mixture. Engine temperature is used for warm up and prevention of overheating. Precise control comes from the feedback of the oxygen sensor. This component provides rich or lean data used for managing the fuel injector. An integrated heater is used for fast transition from open loop to closed loop operation.

The central component of the system is the throttle body assembly, which is composed of an electronic control unit (ECU), fuel injector, temperature and pressure sensors, and mechanical throttle body. With connections to all other components of the system, the throttle body assembly enables precise control of the engine through software algorithms running on the ECU. Using a dual core micro-controller, these algorithms monitor the various sensors in the system and then control the fuel pump module, oxygen sensor heater, fuel injector, and ignition coil.

Integral to the throttle body assembly are multiple temperature and pressure sensors. These devices provide data necessary for consistent engine operation regardless of temperature and altitude. External sensors include engine temperature, crankshaft position, and oxygen sensors.

Operation of the engine begins with turning on the power switch. When turned on, a red MIL located on the throttle body ECU will turn on and off indicating power is on and the light is functional. A constant on of the light indicates a fault code is present and diagnostics are to be performed. With no active MIL, the engine can be started with the pull starter or the electric start. For electric start, the push button commands the engine to start through control by the EFI system. With electronic control of the starter relay, a controlled start is performed where the user is not required to hold the button during the cranking of the engine. A simple switch press creates a command to the EFI system that allows a consistent start of the engine. Start cycle will time out after 5 seconds if engine start is not detected. Once the engine is rotating, the EFI system will begin to control fuel and spark and result in the starting of the engine. A warming phase will occur once started. This warming of the engine is transparent to the operation and requires no special considerations such as a choke or other fuel enrichment controls found on a carbureted unit. After the warm up is completed, the EFI system will begin closed loop control of the air/fuel mixture using the oxygen sensor feedback. Closed loop operation may be briefly canceled during large engine transients such as when a large load is applied.

If any system faults are detected, the MIL will turn on indicating there is an issue with the system. These faults are stored in the ECU and can be retrieved using the EFI Diagnostic Kit. Depending on the fault, the engine may continue to run but have reduced performance and non-compliant emissions. Diagnostics and troubleshooting should be performed if the MIL is on. A qualified technician can access stored fault codes using a cable that plugs into the unit harness and a Windows-based computer. Contact RYOBI Customer Service for more detailed information.