Because there are no contact breaker
points to wear out, the electronic ignition
system is extremely reliable. As long as the
distributor is lubricated, the spark plugs
inspected or renewed at the specified
maintenance intervals, and the leads and
connections kept clean and dry, it is very
unlikely that trouble will be experienced.
Electronic ignition system - fuel
injection models
The ignition system used on fuel injection
models is fully electronic in operation,
incorporating the Electronic Control Unit
(ECU) (situated on the right-hand side of the
engine compartment), a distributor (driven off
the camshaft via a skew gear), a crankshaft
sensor (mounted on the flywheel/torque
converter housing, to register with the reluctor
ring fixed to the rear of the flywheel/torque
converter), as well as the spark plugs, HT
leads, ignition coil, and associated wiring. The
system is divided into two circuits; primary
(low tension/LT) and secondary (high
tension/HT). The primary circuit consists of
the battery, ignition switch, ignition coil
primary windings, ECU and wiring. The
secondary circuit consists of the ignition coil
secondary windings, the distributor cap and
rotor arm, the spark plugs, and the HT leads
connecting these.
The ECU controls both the ignition system
and the fuel injection system, integrating the
two in a complete engine management
package; refer to Chapter 4B for information
relating to the fuel injection side of the system.
As far as the ignition system is concerned,
the ECU receives information in the form of
electrical impulses or signals from the
crankshaft sensor, from the coolant
temperature sensor (which supplies it with
engine temperature), from the throttle pedal
switch (which tells it when the throttle is
closed) and from the manifold absolute
pressure sensor (which gives it the load on the
engine). The crankshaft sensor works in
conjunction with the reluctor ring, which is
bolted onto the back of the flywheel. The
reluctor ring has thirty-four poles on it, spaced
10º apart, with two missing poles 180º apart;
the missing poles identify the cylinder TDC
positions. The sensor reads these poles, to
provide an accurate assessment of the engine
speed and crankshaft position to the ECU.
All the above signals are compared by the
ECU, with set values pre-programmed
(mapped) into its memory; based on this
information, the ECU selects the ignition
timing appropriate to those values, and
controls the ignition coil accordingly.
Note that this means that the distributor is
just that, a distributor of the HT pulse to the
appropriate spark plug; it has no effect
whatsoever on the ignition timing. Also, the
system is so sensitive that, at idle speed, the
ignition timing may be constantly changing;
this should be remembered if trying to check
the ignition timing.
2 Ballasted ignition system
(carburettor models) -
identification
1 As mentioned in Section 1, certain models
may be fitted with a ballasted ignition system
to improve ignition performance when
starting.
2 To determine if a vehicle is equipped with a
ballasted ignition system, check for the
presence of a supplementary wiring harness,
incorporating the white/pink ballast resistor
lead, between the fuse block and the ignition
coil LT terminal.
3 The ballast resistor lead replaces the
original coil feed. The original lead is colour-
coded white, and is retained in the harness to
accommodate vehicles not fitted with a
ballasted system. Do not connect this white
lead to the ignition coil; it must remain taped
to the harness.
4 Failure to observe this warning will result in
coil overheating and premature contact
breaker point failure. Similar damage will
occur if a coil designed for use with a
ballasted system is fitted to a non-ballasted
system, this being due to the excessive
primary current produced. Should it ever be
necessary to renew the coil, ensure that the
replacement is of the correct type.
3 Ignition system (carburettor
models) - testing
2
Contact breaker ignition system
1 By far the majority of breakdown and running
troubles are caused by faults in the ignition
system, either in the low tension or high tension
circuit. There are two main symptoms indicating
ignition faults. Either the engine will not start or
fire, or the engine is difficult to start and
misfires. If it is a regular misfire, ie the engine is
only running on two or three cylinders, the fault
is likely to be in the secondary or high tension
circuit. If the misfiring is intermittent, the fault
could be in either the high or low tension
circuits. If the engine stops suddenly or will not
start at all, it is likely that the fault is in the low
tension circuit. Loss of power and overheating,
apart from carburettor settings, are normally
due to faults in the distributor or incorrect
ignition timing.
Engine fails to start
2 If the engine fails to start and the car was
running normally when it was last used, first
check there is fuel in the fuel tank. If the engine
turns over normally on the starter motor and
the battery is evidently well charged, then the
fault may be in either the high or low tension
circuits. First check the HT circuit. If the
battery is known to be fully charged, the
ignition light comes on and the starter fails to
turn the engine, check the tightness of the
leads on the battery terminals and the security
of the earth lead at its connection on the body
(don’t forget to check the engine to body earth
strap as well). It is quite common for the leads
to have worked loose, even if they look and
feel secure. If one of the battery terminal posts
gets very hot when trying to work the starter
motor, this is a sure indication of a faulty
connection to that terminal.
3 One of the most common reasons for bad
starting is wet or damp spark plug HT leads
and distributor. Remove the distributor cap. If
condensation is visible internally, dry the cap
with a rag and wipe over the HT leads. Refit
the cap and spray the cap, leads and spark
plugs with a water dispersant aerosol.
4 If the engine still fails to start, check that HT
voltage is reaching the spark plugs by
disconnecting each plug lead in turn at the
spark plug end and holding the end of the
cable about 5 mm away from the cylinder
block. If the plug caps are not detachable,
insert a nail or piece of stiff wire into the cap.
Hold the lead with insulating material - eg a
rubber glove, a dry cloth, or insulated pliers.
With the ignition switched on, have an
assistant crank the engine on the starter
motor: a strong blue spark should be seen and
heard to jump from the end of the lead to the
block. If it does, this suggests that HT voltage
is reaching the plugs, and that either the plugs
themselves are defective, the ignition timing is
grossly maladjusted, or the fault is not in the
ignition system. If the spark is weak or absent,
although the cranking speed is good, proceed
with the checks below.
5 Remove the HT lead which enters the
centre of the distributor cap. Hold the end
near the block and repeat the check above. A
good spark now, if there was none at the plug
lead, indicates that HT voltage is not being
transmitted to the plug leads. Check the rotor
arm, distributor cap and HT leads thoroughly
as described in Chapter 1. If there is no spark
at the HT lead from the coil, check the
connections at the coil end of the lead. If it is
in order start checking the low tension circuit
as follows.
6 Separate the contact breaker points with a
piece of paper between their contact faces
then switch on the ignition. Using a 12 volt
voltmeter or a 12 volt bulb and two lengths of
wire, test between the low tension wire to the
coil (marked SW or +) and earth. No reading
indicates a break in the supply from the
ignition switch. Check the wiring and the
connections at the switch and correct any
problems found. A reading on the voltmeter or
illumination of the test bulb indicates that
voltage is reaching the coil and the problem is
therefore a faulty coil, faulty condenser or a
broken lead between the coil and distributor.
7 Remove the condenser from the baseplate
on Lucas distributors or disconnect the
condenser lead on the Ducellier version. With
the contact breaker points open, test between
the moving point and earth. If there is now a
reading then the fault is in the condenser. Fit a
new condenser and the engine should start.
Ignition system 5B•5
5B
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