Marea-Marea Weekend
Engine
9 9 range
Fuel system
10.
BOSCH MOTRONIC ME
3.1
M.P.I. INTEGRATED INJECTION/IGNITION SYSTEM
Introduction
The Bosch Motronic system fitted on the 1998 5 cylinder 20 valve version belongs to the category of
static advance, inductive discharge, digital electronic ignition systems integrated with phased, sequential
type electronic injection systems.
This system has one electronic control unit, a single set of wiring and one set of joint sensors.
Its function is to inject the exact quantity of petrol, into the engine inlet manifold, upstream of the inlet
valves, designed to mix with the air introduced into the cylinder in order to obtain the correct mixture
strength.
The ME 3.1 Motronic system guarantees efficient operation giving optimum performance and consumption
and a reduction in harmful emissions through a prompt response to the different engine operating condi-
tions.
General description of the injection system
There are basically two essential conditions which must always be met for the smooth running of ignition
systems when preparing the air/fuel mixture, namely:
1. the metering (air/fuel ratio) which must be kept as constant as possible and close to the stoichiometric
value to ensure the necessary speed of combustion avoiding pointless fuel consumption;
2. the mixture must be composed of petrol vapours dispersed as finely and evenly as possible in the air.
As far as the optimum metering, on the other hand, is concerned, it is calculated by the control unit fol-
lowing these measurements:
- exact quantity of intake air via the flow meter;
- engine rotation speed via the rpm sensor;
- power requirement via the accelerator pedal potentiometer;
- engine coolant temperature via the sensor on the thermostat support;
- measurement of the exhaust gas oxygen content through the Lambda sensor.
This information is processed by a micro-calculator inside the injection/ignition electronic control unit
which determines the basic injection time through experimentally obtained values which are stored in a
special memory in the above mentioned control unit.
General description of the ignition system
The ignition system is the static advance inductive discharge type (i.e. there is no high tension distributor)
with the power modules inside the electronic control unit.
The system has a single coil for each spark plug; the advantages of this solution are:
- less electrical overload
- guarantee of constant discharge at each spark plug
There is a map in the electronic control unit memory containing the entire series of optimum ignition ad-
vances for the engine operating range according to the engine speed and load conditions.
In the case of detonation it is possible to selectively delay the ignition for the individual cylinder, recog-
nized by the combination of figures transmitted by the detonation sensors and the timing sensor.
Copyright by Fiat Auto
1
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