Fuel dribble (dripping) after injection


This occurs when the fuel supply is not precisely cutoff at the end of fuel injection and fuel particles are accumulated on the tip of the nozzle. If fuel dribble occurs after fuel injection, the fuel in the cylinder will not burn completely. This will result in the emission of black or white smoke being exhausted. To prevent fuel dribble, the relief valve of the delivery valve is designed to draw back any fuel that may drip out of the nozzle after injection. Fuel dribble occurs if there is any failure in the delivery valve or injection nozzle, as the residual pressure remains in the injection pipe after fuel injection.

Diesel EngineBleeding Air for the Fuel System

1. Bleeding the air between the fuel tank and the injection pump (low pressure side)

(1) Repeatedly push down and release the pump handle.

(2) Gradually the pump handle resistance will become higher, and the pump will seize to operate. Then the air flows with the fuel into the fuel tank via the return pipe.

(3) Bleeding the air is completed when the pump handle becomes hard to operate.


In following cases, bleed the air between the injection pump and injection nozzle (high pressure side).

When the engine does not operate properly after the engine is warmed up

When a part on the high pressure side of the fuel system are replaced

2. Bleeding the air between the injection pump and the injection nozzle (high pressure side)

(1) Loosen all injection pipe union nuts on the nozzle holder side.

(2) Crank the engine to force the fuel out of the injection pipe and bleed the air.

(3) Tighten the injection pipe union nuts.


In the case of the common-rail type, use the hand-held tester and operate the injector to bleed the air. Do not bleed the air with the injection pipe union nuts loosened.

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