Contaminants-in-Fuel Diagnosis
Fungi and other microorganisms can survive and multiply in diesel fuel if water is present. The fungi can be present in any part of the fuel handling system. These fungi grow into long strings and will form into large globules. The growths appear slimy and are usually black, green, or brown. The fungi may grow anywhere in the fuel but are most plentiful where diesel fuel and water meet. As the fuel is agitated, when service station tanks are being filled, fungi are distributed throughout the tank and may be pumped into a vehicle.
Fungi use the fuel as their main energy supply and need only trace amounts of water and minerals. As they grow and multiply, they change fuel into water, sludge, acids, and products of metabolism. The most common symptom is fuel filter plugging, however various metal fuel system components including fuel sender assembly, pipes, fuel injectors, and fuel injection pump can corrode.
Warning: Avoid physical contact with the biocides in order to avoid personal injury.
If fungi have caused fuel system contamination, use a diesel fuel biocide to sterilise the fuel system. Do not exceed the dosage recommended on the label. Discontinue the use of a biocide when towing a trailer. It is permissible to have biocide in the fuel when starting to tow, but do not add any biocide while towing.
Water in fuel will also create driveability concerns and loss of engine power. If water is present in the fuel system, the fuel cannot cool and lubricate the components, causing overheating, rust and corrosion. This can result in component failure. Water can enter the fuel system in several ways, either through a contaminated refuelling source, or through long term condensation in the vehicle fuel tanks.
Like fungi and water, petrol contamination will cause driveability concerns and a possible hard starting or a no start condition if the overall content is high enough. Petrol raises the API rating and reduces cooling and lubrication, resulting in possible component failure.
Inspecting for Fuel Contaminants
| • | Remove the fuel filter and inspect the inside area of the fuel filter for dirt, water deposits, or other debris. |
| • | Drain the fuel filter into an approved clear container and allow the contents to settle. Observe the container for contaminant separation. |
| | Note: The presence of water or petrol in diesel fuel may also cause damage to other fuel system components. |
| • | Remove the water-in-fuel sensor from the bottom of the fuel filter and inspect inside the filter for rust deposits, dirt, or other debris. |
| • | If contaminants are present in the fuel or in any of the inspected areas, remove the fuel lines to the injectors and inspect the fuel injector return outlets and feed inlets for rust or corrosion. |
| ⇒ | If rust or corrosion was not present in the injectors, but contaminated fuel was present, refer to Fuel System Cleaning and attempt to start and run the engine after procedure is completed. |
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