From Advanced Automotive Fault Diagnosis, Second Edition

7.5 Diagnostics fuel system

7.5.1 Systematic testing example

If the reported fault is excessive fuel consumption proceed as follows.

  1. Check that the consumption is excessive for the particular vehicle. Test it yourself if necessary.

  2. Are there any other problems with the vehicle, misfiring for example or difficult starting?

  3. For example if the vehicle is misfiring as well this may indicate that an ignition fault is the cause of the problem.

  4. Remove and examine spark plugs, check HT lead resistance and ignition timing. Check CO emissions.

  5. Renew plugs and set fuel mixture.

  6. Road test vehicle for correct engine operation.

7.5.2 Test equipment


You should always refer to the manufacturer's instructions appropriate to the equipment you are using.

Exhaust gas analyser (Figure 7.9)

Figure 7.9: Exhaust gas analyser

This is a sophisticated piece of test equipment used to measure the make up of the vehicle's exhaust gas. The most common requirement is the measuring of carbon monoxide (CO). A sample probe is placed in the exhaust tail pipe or a special position before the catalytic converter if fitted, and the machine reads out the percentage of certain gases produced. A digital readout is most common. The fuel mixture can then be adjusted until the required readings are obtained.

Fuel pressure gauge

The output pressure of the fuel pump can be tested to ensure adequate delivery. The device is a simple pressure gauge but note the added precautions necessary when dealing with petrol.

7.5.3 Test results

Some of the information you...

Products & Services
Combustion Engines
Industrial engines are heavy-duty, internal combustion engines that are used to power and propel vehicles, machinery, and equipment. They burn a liquid or gaseous fuel such as gasoline, diesel, biodiesel, propane, or natural gas.
Carburetors are devices used to proportionally mix a fuel with air for a combustion process.
Fuel Dispensing Equipment
Fuel dispensing equipment dispenses and monitors all types of liquid and gaseous fuel.
Flame Arrestors
Flame arrestors are safety devices for handling combustible gases. They prevent gas from burning back into a device and exploding.
Fuel Cell and Solar Test Equipment
Battery, fuel cell and solar test equipment consists of specialized test stations, stands or systems, monitors and component modules for performance or endurance testing.

Topics of Interest

7.6 Introduction to engine management Engine management is a general term that describes the control of engine operation. This can range from a simple carburettor to control or manage the fuel, with...

7.3 Diagnostics engines 7.3.1 Systematic testing example If the reported fault is excessive use of engine oil proceed as follows. Question the customer to find out how much oil is being used.

7.10 Diagnostics emissions 7.10.1 Testing procedure If the reported fault is incorrect exhaust emissions the following procedure should be utilised. Figure 7.24 is typical of the emissions data...

1.6 Cycles of operation The basic function of an engine is to convert chemical energy (the fuel) into mechanical energy and to produce usable power and torque (this is the ability to turn the driving...

2.1 Introduction 2.1.1 Logic Diagnostics or faultfinding is a fundamental part of an automotive technician's work. The subject of diagnostics does not relate to individual areas of the vehicle. If...

Product Announcements
Hilliard Corporation (The)
Ingersoll Rand Industrial Technologies / Air Motors
Ingersoll Rand Industrial Technologies / Air Motors