FUEL PUMPS

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The fuel pumps are used to control when, and how much fuel is injected into the cylinder, from the joint inputs of governor (fuel rack) and camshaft (fuel cam). It is the fuel pump that generates the high fuel pressure that enables the fuel injector to operate correctly to atomise and distribute the fuel within the cylinder.

The governor input to each fuel pump will be identical when new, and this output quantity can be changed by adjusting the fuel rack to each pump. This operation would be carried out to power balance the engine, and compensate for internal leakage within the pump element.

NB When a fuel pump is replaced the governor linkage should be checked so that no fuel injection occurs at zero position, and that full movement is possible. Also check that both the governor and fuel cut-off can reduce the fuel rack to zero.

The point in the engine cycle at which the fuel is injected into the cylinder is critical. Early fuel injection (usually achieved only by timing mal-adjustment) will increase mechanical stresses on the cylinder components, whilst late fuel injection decreases fuel efficiency, and increases smoke and exhaust gas temperature levels.

Fuel pump timing is carried out whilst the engine is stopped. There are various methods by which this can be accomplished, and two manufacturer's methods are detailed below.

MaK medium speed engine types M452/453C

a)            Bar the engine to the position of commencement of fuel delivery for that cylinder

b)            Check the window on the fuel pump to ensure that the upper mark on the body coincides with the moving mark on the tappet bucket (FIG b)

c)            If the two marks do not coincide bar the engine away from top dead centre and check that the lower mark on the body coincides with the moving mark on the tappet bucket (FIG c)

d)           

Remove the fuel pump and slacken the locking screw (4) and adjust the thrust screw (5) (FIG d). Replace the fuel pump and check the commencement of fuel injection using methods a) and b) above. Continue to adjust until the fuel setting is correct.