A tappet and plunger assembly adapted for fluid injection pump, such as unit fuel injector. The fuel pump plunger is retained directly to the tappet by a flexible member such as an elastomeric o-ring. If the plunger seizes in its housing bore, the flexible member will sufficiently flex and/or fail thereby allowing the tappet to i) separate from the stationary plunger and ii) remain in contact with the mating component of the moving engine drive train. The arrangement helps prevent damage to the engine by engine drive train components if the plunger becomes seized.