DIAGNOSIS

Injectors must function correctly to achieve satisfactory engine performance. The nozzle has a particular function, which is to inject a finely atomised spray of fuel into the combustion chamber. Faulty injectors, which will be unable to perform that function, can cause misfiring, engine knock, engine overheating, loss of power, smoky black exhaust, or increased fuel consumption. (These are similar symptoms to a faulty spark plug in a petrol engine.) Injectors should be removed for cleaning and testing at the recommended maintenance periods.

A faulty injector can be located by loosening off the injector pipe at each injector in turn, with the engine running at idle. This cuts off the fuel supply to the particular injector and causes a noticeable drop in engine speed for a good injector. However, no change in speed will occur with a faulty injector. In this way, the faulty injector can be isolated.

Since this is the same procedure as that used for bleeding the injector pipes, any air in the pipes will be bled at the same time as the injector is being checked.

In some cases, alternative methods are used to locate a faulty injector. This can be by using special crayons that change colours at certain temperatures. The crayon is applied to each individual exhaust manifold branch, just after the cylinder head. If no change or incorrect colour on a particular port is noticed. It is possible that the cylinder in question is not functioning, therefore not generating sufficient heat to produce power. This would then be apparent by the lack of colour change on that manifold port or branch . Also whilst the engine is still relatively cold from initial start up. Carefully feeling each port will also indicate a misfiring cylinder if one port is colder than the rest.

Note: Although a fuel problem may exist, it could be a pumping element within the FIP at fault.

However it must be appreciated that if a cylinder is misfiring, the cause may not NECESSARILY be a faulty injector. There are several other reasons for misfiring only on one cylinder.

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