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.