  We present a new set of high-resolution molecular line maps of the gas
immediately surrounding various Herbig-Haro (HH) knots of the giant HH flow HH
315, from the young star PV Cephei. The observations, aimed at studying the
entrainment mechanism of the 2.6 pc-long HH 315 flow, include IRAM 30m maps of
the 12CO(2-1), 12CO(1-0), and 13CO(1-0) lines, with beam sizes of 11'', 21'',
and 22'', respectively. We compare the morphology and the kinematics of the
outflow gas, as well as the temperature and momentum distribution of the
molecular outflow with those predicted by different entrainment models. With
our detailed study we are able to conclude that jet bow shock entrainment by an
episodic stellar wind, with a time-varying axis, produces most of the
high-velocity molecular outflow observed far from the source. In addition, near
PV Cephei we find evidence for a poorly collimated, wide-angle, molecular
outflow and a collimated wiggling jet-like molecular outflow. We propose that
the poorly collimated component is entrained by a wide-angle wind, and the
collimated component is entrained by a variable jet with internal working
surfaces. If this picture is true, then a stellar wind model which allows for
the coexistence of a wide-angle component and a collimated (jet-like) stellar
wind component is needed to explain the observed properties of the PV Ceph
outflow. The wiggling axis of the redshifted molecular outflow lobe indicates
that the outflow ejection axis is changing over time. We find that the
time-scale of the axis variation shown by the molecular outflow lobe is about a
factor of 10 less than that shown by the large-scale optical HH knots.
