This sounds like something you can fix with AutoCAD rather than cadMEP settings. Maybe you could post a picture of what is wrong?

LWDisplay set to ON and changing your layer lineweights (in the cadMEP services) to be thicker might be what your looking for, but without a better idea of what your seeing it is hard to say.

After you've tweaked those settings, be sure to do a RebuildAll to regenerate the layers on the existing objects.