service interval reset FORD FIESTA 1989 Service Repair Manual

flux can pass between the magnet and the
sensor. When a trigger vane segment is in line
with the sensor, the magnetic flux is diverted
through the trigger vane, away from the
sensor. The sensor detects the change in
magnetic flux and sends an impulse to the
EEC IV module. Additional data is received
from the engine coolant temperature sensor,
manifold absolute pressure sensor, inlet air
temperature sensor, throttle position sensor
and vehicle speed sensor. Using this
information the EEC IV module calculates the
optimum ignition advance setting and
switches off the low tension circuit via the
ignition module. This results in the collapse of
the magnetic field in the coil which generates
the high tension voltage. The high tension
voltage is then fed, via the coil HT lead and
the carbon brush in the centre of the
distributor cap, to the rotor arm. The voltage
passes across to the appropriate metal
segment in the cap and via the spark plug HT
lead to the spark plug where it finally jumps
the spark plug gap to earth. It can be seen
that the ignition module functions basically as
a high current switch by controlling the low
tension supply to the ignition coil primary
windings.In the event of failure of a sensor, the
EEC IV module will substitute a preset value
for that input to allow the system to continue
to function. In the event of failure of the
EEC IV module, a “limited operation strategy”
(LOS) function allows the vehicle to be driven,
albeit at reduced power and efficiency. The
EEC IV module also has a “keep alive
memory” (KAM) function which stores idle and
drive values and codes which can be used to
indicate any system fault which may occur.
Distributorless ignition systems
The main ignition system components
include the ignition switch, the battery, the
crankshaft speed/position sensor, the ignition
module, the coil, the primary (low tension/LT)
and secondary (high tension/HT) wiring
circuits, and the spark plugs. The system used on carburettor models is
termed DIS (Distributorless Ignition System),
and on fuel injection models E-DIS, (Electronic
Distributorless Ignition System). The primary
difference between the two is that the DIS
system is an independent ignition control
system while the E-DIS system operates in
conjunction with the EEC IV engine
management module which also controls the
fuel injection and emission control systems.
With both systems, the main functions of
the distributor are replaced by a computerised
ignition module and a coil unit. The coil unit
combines a double-ended pair of coils - each
time a coil receives an ignition signal, two
sparks are produced, at each end of the
secondary windings. One spark goes to a
cylinder on compression stroke and the other
goes to the corresponding cylinder on its
exhaust stroke. The first will give the correct power stroke, but the second spark will have
no effect (a “wasted spark”), occurring as it
does during exhaust conditions.
The ignition signal is generated by a
crankshaft position sensor which scans a
series of 36 protrusions on the periphery of
the engine flywheel. The inductive head of the
crankshaft position sensor runs just above the
flywheel periphery and as the crankshaft
rotates, the sensor transmits a pulse to the
ignition module every time a protrusion
passes it. There is one missing protrusion in
the flywheel periphery at a point
corresponding to 90° BTDC. The ignition
module recognises the absence of a pulse
from the crankshaft position sensor at this
point to establish a reference mark for
crankshaft position. Similarly, the time interval
between absent pulses is used to determine
engine speed. On carburettor engines, the ignition module
receives signals provided by information
sensors which monitor various engine
functions (such as crankshaft position,
coolant temperature, inlet air temperature,
inlet manifold vacuum etc). This information
allows the ignition module to generate the
optimum ignition timing setting under all
operating conditions.
On fuel injection engines, the ignition
module operates in conjunction with the
EEC IV engine management module, and
together with the various additional
information sensors and emission control
components, provides total control of the fuel
and ignition systems to form a complete
engine management package. The information contained in this Chapter
concentrates on the ignition-related
components of the engine management
system. Information covering the fuel, exhaust
and emission control components can be
found in the applicable Parts of Chapter 4.
Precautions
When working on the ignition system, take
the following precautions:
a) Do not keep the ignition switch on for
more than 10 seconds if the engine will
not start.
b) If a separate tachometer is ever required
for servicing work, consult a dealer
service department before buying a
tachometer for use with this vehicle -
some tachometers may be incompatible
with these types of ignition systems - and
always connect it in accordance with the
equipment manufacturer’s instructions.
c) Never connect the ignition coil terminals to earth. This could result in damage to
the coil and/or the ignition module.
d) Do not disconnect the battery when the
engine is running.
e) Make sure that the ignition module is
properly earthed.
f) Refer to the warning at the beginning of the next Section concerning HT voltage.
2 Ignition system - testing
2
Warning: Voltages produced by
an electronic ignition system are
considerably higher than those
produced by conventional
ignition systems. Extreme care must be
taken when working on the system with
the ignition switched on. Persons with
surgically-implanted cardiac pacemaker
devices should keep well clear of the
ignition circuits, components and test
equipment.
Note: Refer to the precautions given in
Section 1 of Part A of this Chapter before
starting work. Always switch off the ignition
before disconnecting or connecting any
component and when using a multi-meter to
check resistances.
1 If the engine turns over but won’t start,
disconnect the (HT) lead from any spark plug,
and attach it to a calibrated tester (available at
most automotive accessory shops). Connect
the clip on the tester to a good earth - a bolt
or metal bracket on the engine. If you’re
unable to obtain a calibrated ignition tester,
have the check carried out by a Ford dealer
service department or similar. Any other form
of testing (such as jumping a spark from the
end of an HT lead to earth) is not
recommended, because of the risk of
personal injury, or of damage to the ignition
module.
2 Crank the engine, and watch the end of the
tester to see if bright blue, well-defined sparks
occur.
3 If sparks occur, sufficient voltage is
reaching the plug to fire it. Repeat the
check at the remaining plugs, to ensure
that all leads are sound and that the
coil is serviceable. However, the plugs
themselves may be fouled or faulty, so
remove and check them as described in
Chapter 1.
4 If no sparks or intermittent sparks occur,
the spark plug lead(s) may be defective. Also,
on distributor systems, there may be
problems with the rotor arm or distributor cap
- check all these components as described in
Chapter 1.
5 If there’s still no spark, check the coil’s
electrical connector (where applicable), to
make sure it’s clean and tight. Check for full
battery voltage to the coil at the connector’s
centre terminal. Check the coil itself (see
Section 3). Make any necessary repairs, then
repeat the check again.
6 The remainder of the system checks should
be left to a dealer service department
or other qualified repair facility, as there is a
chance that the ignition module may
be damaged if tests are not performed
properly.
Ignition system 5B•3
5B
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