Fuel System Cleaning: Notes

Diesel Exhaust Fluid (DEF) is a corrosive fluid that also tends to form deposits on components. In case of DEF contamination in the fuel tank, follow the guidelines below.

If the in-tank fuel pump has been run, then it must be assumed that DEF has been pumped through both the low-pressure system and high-pressure pump. For this case, there are two scenarios:

1. Engine has not been cranked. In this case, the system from fuel fill pipe to the high-pressure fuel pump and the high-pressure pipe from pump to rail must be replaced along with the low-pressure return lines.
2. Engine has been cranked. In this case, the entire fuel system from fuel fill pipe to high-pressure fuel pump, fuel rail, injectors, injector return fuel lines, high-pressure fuel pipes and low pressure return lines must be replaced.

If the in-tank fuel pump has not been run, the fuel fill pipe, tank and fuel pump module should be replaced.

The following procedure should not be used for cases of DEF contamination.

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 components including the fuel sending unit, pipes, fuel injectors, and injection pump can corrode.

If bacterial growth is found in the fuel system, the proper method of removal is to flush the fuel system using the appropriate Service Information procedures, replace the fuel filter element and refill the tank with clean diesel fuel. Fuel system flushing should be conducted using a GM recommended or regional equivalent diesel fuel system cleaner.

The presence of water or gasoline in diesel fuel may also cause injection pump and nozzle damage.

This procedure checks for the presence of water, gasoline and fungi/bacteria in diesel fuel that may cause injection pump and nozzle damage.

Remove and inspect the fuel filter element.

• If water, gasoline or fungi/bacteria are not present, end the inspection.
• If water or fungi/bacteria are present, proceed to Cleaning Water from the Fuel System.
• If gasoline is present, proceed to Cleaning Gasoline from the Fuel System.