Stepper Motor - PIAGGIO 500 cc Service Manual

Reset must be carried out in the following cases:
- on initial assembly
- when the throttle body is replaced
- when the fuel injection control unit is replaced.
NOTE
The TPS reset procedure must not be carried out on a used throttle body, in that possible wear of the throttle and
the minimum opening stop, render the air flow different from that of precalibration.

STEPPER MOTOR

CIRCUIT DIAGRAM
1 CONTROL UNIT
The throttle body is supplied with an auxiliary air circuit. This is activated more or less by a piston valve controlled
by a stepper.
The stepper is fed by the control unit only when necessary to vary the opening.
Revolution is subdivided in rev fractions called "steps".
By varying the opening "steps", it is possible to adequately feed the engine to facilitate the ignition procedure and
correct the cold engine air feed.
When the engine reaches normal running temperature, the stepper is partly closed.
To avoid anomalous wear on the adjusting piston, the speed functioning is achieved with a minimum opening of
around 20 "steps".
To recover any adjustments, when ignition is set to "OFF", the piston closes completely and reopens by the number
of steps pre-established (autoreset).
When the control unit modifies the opening "steps" of the stepper, it also modifies the fuel injection timing to guarantee
that correct carburation is maintained.
Idling speed is practically stable 1450-50 rpm. After a warm starting phase the first revolutions increase is perceivable
with the subsequent closure of the stepper to stabilize the speed.
On revealing speed irregularities, before proceeding with electrical controls, check accurately the cleanliness of the
throttle and the auxiliary air circuit.
2
1
14
24
21
6
2 STEPPER
Fuel injection
9
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