(1) Inspect the plunger for scratches and rust; replace with a new one if necessary.
(2) Check the plunger assembly fit. Insert the plunger end into the plunger sleeve at approximately 60°. If the plunger slides down slowly under its own weight, the fit is good.
(3) Check the plunger assembly seal. Hold the plunger sleeve with one hand and block the oil inlet at the top and side of the plunger with two fingers. Pull out the plunger with the other hand. If you feel a strong suction, and the plunger immediately retracts to its original position when you release it, the plunger assembly seal is good; otherwise, replace the plunger assembly.
(4) Check the pressure reducing ring of the delivery valve assembly for wear, steps, or scratches; replace if necessary.
(5) Check the delivery valve assembly fit. Block the lower hole of the delivery valve with one finger and gently press the delivery valve downwards with another finger. If it automatically springs back to its original position when you remove your finger, the delivery valve assembly seal is good; otherwise, replace the delivery valve assembly.
(6) Inspect the tappet. The standard clearance between the fuel injection pump body and the tappet is 0–0.03 mm. If it exceeds 0.2 mm, the part should be replaced.
(7) Check the clearance between the plunger flange and the groove of the control sleeve. It should be 0.02–0.08 mm. If it exceeds 0.12 mm, the control sleeve must be replaced.
