If your low efficiency is from machines stopping and starting due to inconsistent product flow, then line integration in the form of speed modulation may be your best solution. If your downtime is related to replenishment of supplies, such as film for an over wrapper, then additional buffering through accumulation will increase your line efficiencies.
In the simplest form you can manually track the downtime with a pencil and paper. Since most operator interfaces have built in historians, adding one to your system is a cost effective approach to identifying trends. Typically data is gathered in the Logic Controller from tag values used in line integration and error detection, this information is then just displayed on the operator interface.
If the existing equipment will run at the required rates, the question becomes why fix something that isn't broken? Consider the life cycle stage of the machine: If the cost to upgrade an older machine to the level of communications required for line integration - is significant - then you might just consider replacing the machine. On the other hand, upgraded controls could realize the savings in efficiencies due to reduced downtime because of the improved diagnostics.