Marine Engine-Q & A - Fuel Pump

Q: Explain how a fuel pump may be checked for accuracy of injection timing.


A:  With a jerk type fuel pump, injection starts when the top edge of the plunger cuts off the spill ports as the plunger is moving upwards on the delivery stroke.To check the accuracy of the start of injection, the engine crank angle for the start of injection must correspond to the manufacturers setting when the plunger is at this point.

On the some pumps it is possible, after isolating the fuel and draining the pump, to remove erosion plugs and sight through the spill ports while turning the engine.At the point where the edge of the plunger is seen to cover the top of the spill port, the crank angle for that particular unit is noted and copared with the manufacturers recommendation.
On the other hand it may be necessary to remove the cover of the pump and the delivery valve and measure the distance from the top of the barrel to the top of the plunger.The manufacturer will give the correct distance at which the plunger has covered the spill ports.Alternatively the distance to the top of the plunger when the unit is on TDC may be given