Fuel fault diagnosis table 1 diplomatic!
7.5.4 Fuel fault diagnosis table 1 diplomatic!
Black smoke from Excessively rich Look up correct
settings and adjust Symptom
exhaust
mixture
Possible faults
Suggested action
Flooding
Check and adjust carburettor float
No fuel at Empty tank!
settings and carburettor or
Fill it!
Blocked filter or line Replace filter, operation
108 Advanced automotive fault diagnosis
7.5.5 Fuel fault diagnosis table 2
approximately 8 kV is required. For higher com- pression ratios and weaker mixtures, a voltage up
Symptom
Possible cause
to 20 kV may be necessary. The ignition system has to transform the normal battery voltage of
Excessive consumption
Blocked air filter
12 V to approximately 8 to 20 kV and, in addition,
Incorrect CO adjustment Fuel injectors leaking
has to deliver this high voltage to the right cylin-
Ignition timing incorrect
der, at the right time. Some ignition systems will
Temperature sensor fault
supply up to 40 kV to the spark plugs.
Load sensor fault
Conventional ignition is the forerunner of the
Low tyre pressures
more advanced systems controlled by electron-
Driving style!
ics. However, the fundamental operation of most
Fuel leakage
Damaged pipes or unions Fuel tank damaged
ignition systems is very similar; one winding of a
Tank breathers blocked
coil is switched on and off causing a high voltage
Fuel smell
Fuel leak
to be induced in a second winding. A coil igni-
Breather incorrectly fitted
tion system is composed of various components
Fuel cap loose
and sub-assemblies; the actual design and con-
Engine flooding
struction of these depend mainly on the engine
Incorrect emissions
Incorrect adjustments
with which the system is to be used.
Fuel system fault Air leak into inlet Blocked fuel filter
7.7.2 Advance angle (timing)
Blocked air filter Ignition system fault
For optimum efficiency the ignition advance angle should be such as to cause the maximum combustion pressure to occur about 10° after
7.6 Introduction to engine
TDC. The ideal ignition timing is dependent on
management
two main factors, engine speed and engine load. An increase in engine speed requires the ignition
Engine management is a general term that timing to be advanced. The cylinder charge, of describes the control of engine operation. This can
air fuel mixture, requires a certain time to burn range from a simple carburettor to control or man-
(normally about 2 ms). At higher engine speeds age the fuel, with an ignition distributor with con-
the time taken for the piston to travel the same tact breakers to control the ignition to a very
distance reduces. Advancing the time of the spark sophisticated electronic control system. The funda-
ensures that full burning is achieved. mental tasks of an engine management system are
A change in timing due to engine load is also to manage the ignition and fuelling, as well as other
required as the weaker mixture used on low load aspects, and to refine the basic control of an engine.
conditions burns at a slower rate. In this situation Many of the procedures and explanations in this
further ignition advance is necessary. Greater load chapter are generic. In other words the ignition
on the engine requires a richer mixture, which system explained in the next sections may be the
burns more rapidly. In this case some retardation same as the system used by a combined ignition
of timing is necessary. Overall, under any condi- and fuel control system.
tion of engine speed and load an ideal advance angle is required to ensure maximum pressure is achieved in the cylinder just after TDC. The ideal
7.7 Ignition
advance angle may also be determined by engine temperature and any risk of detonation.