Fiat 1998 Marea Weekend, Service Manual

Page: 144 / 846

Engine
Fuel system
Marea-Marea Weekend®^
1998 range
10.
The rising side of signal (graph B in figure on previous page) therefore represents a moment within
which alternative primary winding conduction could take place. This point can be established only by
the control unit power module. The conduction time the H.T. coil needs in order to store sufficient ener-
gy is also defined by DWELL management strategies. This depends on the time taken by the current to
reach about 6A in the coil primary winding and also on the calculation algorithm run by the micropro-
cessor which uses factors saved in a special memory, obviously based on engine rpm
With reference to the figure on the previous page, the falling side of the signal, (B) conduction end point (or
current drop to zero), is a categorical order to cut-off the current flowing in the primary winding and repre-
sents the ignition advance point (a) processed by the computer (advance - (a) - varies according to rpm).
The control unit (ECU) then controls spark advance in the different cylinders in relation to top dead cen-
tre and conduction time necessary for the coil to store energy by controlling the two power stages (cor-
responding to ECU pins 59 and 66). These in turn permit current to flow through primary windings of
coils (6) for long enough to ensure the specified 6A current rating.
I
^unj~ijiLn r u
4jTn_r_
J ~ L T L B | / ~
59
66
+ 12V
Ignition operating diagram
1. RPM and TDC sensor.
2. Phonic wheel.
3. Signal pattern taken from phonic wheel
(60-2) teeth.
TDCs correspond to teeth 20 and 50.
4.Succession of rectangular square wave sig-
nals of constant amplitude
5. Ignition power module ()inside control
unit.
6. Ignition coils.
7. Spark plugs
NOTE The numbers in boxes indicate the corresponding control unit pins
At the moment when the ECU de-activates one of the two power stages, current flow is cut off. This
generates a voltage by induction (up to 30kV without loads) in the secondary winding.
10
Publication no. 506.763/09