Jerk type fuel pump::
With a jerk type fuel pump , the fuel pressure starts to rise when the tip edge of the plunger cutt off the spill ports as the plunger ismoving upward on the delivery stroke. To check the accurancy of the start of injection , the engine crank angle for the start of injection must correspond to the manufacturer setting when the plunger is at this point
Method I ::
On some pump it is possible after isolating the fuel and draining the pump , to remove erosion plug and sight through the spill port while turning the engine. At the point where the edge of the plunger is seen to cover the top of thr spill port , the crank angle for that particular unit is noted and compared with the manufacturer recommendation.
On some pumps i may be necessary to remove the top cover of the pump and delivery valve and measure the distance from thr top of the barrel to the top of the plubger.The manufacturer will give the correct distance at which the plunger has covered the spill ports
Timing can be adjusted by altering the position of fuel cam on the camshaft . This is done by hydraullically expanding the cam on the cam shaft .
On some other pumps , small adjustment can be made by adjusting relative height of the plunger and barrel by placing the shims under thr foot of the plunger or under the fuel pump body in which the plunger is located.
On pumps fitted with VIT start of injection can be adjusted using ViT rack for individual pumps