This work presents a methodology to adjust the electronic control system of a reciprocating internal combustion engine test bench and the effect of the control parameters on emissions produced by the engine under two extreme situations: unadjusted and adjusted, both under transient operation. The aim is to provide a tuning guide to those in charge of this equipment not needed to be experts in control engineering. The proposed methodology covers from experimental plant modelling to control parameters determination and experimental validation. The methodology proposed includes the following steps: (i) Understanding of test bench and mathematical modeling; (ii) Model parameters identification; (iii) Control law proposal and tuning from simulation and (iv) Experimental validation. The work has been completed by presenting a comparative experimental study about the effect of the test bench control parameters on engine performance profiles (engine speed, engine torque and relative fuel air ratio) and on regulated gaseous emissions (nitrogen oxides and hydrocarbons concentrations) and the profile of number of particles emitted. The whole process, including experimental validation, has been carried out in a test bench composed of a turbocharged, with common rail injection system, light duty diesel engine coupled to a Schenck E-90 eddy current dynamometric brake and its related Schenk X-act control electronics. The work demonstrates the great effect of the test bench control tuning under transient operation on performance and emissions produced by the engine independently of the engine accelerator position demanded before and after the test bench tuning.