Derbi Rambla 250, Manual, Page: 144 / 259

MIU injection system
This is an integrated ignition and injection system.
Injection is indirect in the manifold through an electro-injector.
Injection and ignition are timed on the 4-stroke cycle using a tone wheel keyed onto the crankshaft (24-2
teeth) and a reluctant variation (pick-up) sensor.
Carburetion and ignition are managed on the basis of the engine revs and throttle valve opening. Further
corrections are made according to the following parameters:
- Coolant temperature
- Intake air temperature
- Lambda probe value
The system implements an idle supply correction with cold engine through a Stepper motor on a by-
pass circuit of the throttle valve. The electronic control unit manages the Stepper motor and the injector
opening time, thereby ensuring idle steadiness and proper carburetion.
In all conditions of use, carburetion is controlled by modifying the injector opening time.
Fuel delivery pressure is kept constant based on the ambient pressure.
The
fuel supply circuit
consists of:
- Fuel pump
- Fuel filter
- Injector
- Pressure regulator
Pump, filter and regulator are placed into the fuel tank using a single support.
The injector is connected by two pipes provided with fast-release fittings. This results in a continuous
circulation, thereby avoiding the risk of fuel boiling. The pressure regulator is at the end of the circuit.
The fuel pump is controlled by the MIU control unit; therefore the scooter's safety is enhanced.
The
ignition circuit
consists of:
- HV coil
- HV cable
- Shielded cap
- MIU control unit
- Spark plug
The MIU control unit manages the ignition with the best advance ensuring 4-stroke timing (ignition only
in the compression stroke) at the same time.
The MIU injection-ignition system controls engine functions by means of a pre-set program.
Should any input signals fail, an acceptable working order of the engine is ensured to allow the user to
reach a service station.
Obviously, this cannot happen when the rev counter signal is missing, or when the failure concerns the
control circuits:
- Fuel pump
Injection
INJEC - 144