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

Note

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...

Copyright Tom Denton 2006 under license agreement with Books24x7

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