  We study how the exotic particles and supersymmetric partners would affect
the discovery limit at the Tevatron and LHC for neutral gauge bosons in generic
E_6 models. We examine the Z' decay in the extreme case that all of the
particles are massless, then consider how the masses of non-standard model
particles will affect the discovery limit. We also calculate the discovery
limit for a supersymmetric E_6 model with a secluded sector as a concrete
example of a model with a definite set of exotic particles. Its discovery limit
is small compared with other E_6 models due to the U'(1) charge assignment.
