An inferential exhaust manifold pressure detection device comprising: an exhaust gas recirculation valve having a first input, an output and a second input; an exhaust manifold of an engine having an output connected to the first input of the EGR valve and to an input of a turbine, and having an input connected to exhaust ports of cylinders of the engine; an intake manifold of the engine having an input connected to the output of the EGR valve and to an output of a compressor, and an output connected to intake ports of the cylinders; a pressure sensor situated in the intake manifold; and a processor having an input connected to the pressure sensor and an output; and wherein: the processor is configured to calculate an inlet pressure of the EGR valve based on a pressure from the pressure sensor, a turbine power versus compressor power balance in view of an efficiency of the turbine and an efficiency of the compressor, and flow equations representing a mass conservation of the engine, wherein the inlet pressure of the EGR valve is essentially equal to a pressure in the exhaust manifold; and wherein the processor is configured to detect one or both of an EGR valve failure and an intake air leakage failure when a turbocharger efficiency is in an Efficiency Island, wherein both of the compressor and the turbine have high, substantially flat, and almost constant efficiencies at an area of operating points defining the Efficiency Island and wherein the turbine efficiency and the compressor efficiency fall rapidly to zero along a border of the Efficiency Island; wherein the processor is blocked from detecting an EGR valve failure and an intake air leakage failure when the turbocharger efficiency is outside of the Efficiency Island, and wherein the processor is configured to determine a control signal for the EGR valve based on the calculated inlet pressure of the EGR and outputs the control signal to the EGR valve. an exhaust gas recirculation valve having a first input, an output and a second input; an exhaust manifold of an engine having an output connected to the first input of the EGR valve and to an input of a turbine, and having an input connected to exhaust ports of cylinders of the engine; an intake manifold of the engine having an input connected to the output of the EGR valve and to an output of a compressor, and an output connected to intake ports of the cylinders; a pressure sensor situated in the intake manifold; and a processor having an input connected to the pressure sensor and an output; and wherein: the processor is configured to calculate an inlet pressure of the EGR valve based on a pressure from the pressure sensor, a turbine power versus compressor power balance in view of an efficiency of the turbine and an efficiency of the compressor, and flow equations representing a mass conservation of the engine, wherein the inlet pressure of the EGR valve is essentially equal to a pressure in the exhaust manifold; and wherein the processor is configured to detect one or both of an EGR valve failure and an intake air leakage failure when a turbocharger efficiency is in an Efficiency Island, wherein both of the compressor and the turbine have high, substantially flat, and almost constant efficiencies at an area of operating points defining the Efficiency Island and wherein the turbine efficiency and the compressor efficiency fall rapidly to zero along a border of the Efficiency Island; wherein the processor is blocked from detecting an EGR valve failure and an intake air leakage failure when the turbocharger efficiency is outside of the Efficiency Island, and wherein the processor is configured to determine a control signal for the EGR valve based on the calculated inlet pressure of the EGR and outputs the control signal to the EGR valve. the processor is configured to calculate an inlet pressure of the EGR valve based on a pressure from the pressure sensor, a turbine power versus compressor power balance in view of an efficiency of the turbine and an efficiency of the compressor, and flow equations representing a mass conservation of the engine, wherein the inlet pressure of the EGR valve is essentially equal to a pressure in the exhaust manifold; and wherein the processor is configured to detect one or both of an EGR valve failure and an intake air leakage failure when a turbocharger efficiency is in an Efficiency Island, wherein both of the compressor and the turbine have high, substantially flat, and almost constant efficiencies at an area of operating points defining the Efficiency Island and wherein the turbine efficiency and the compressor efficiency fall rapidly to zero along a border of the Efficiency Island; wherein the processor is blocked from detecting an EGR valve failure and an intake air leakage failure when the turbocharger efficiency is outside of the Efficiency Island, and wherein the processor is configured to determine a control signal for the EGR valve based on the calculated inlet pressure of the EGR and outputs the control signal to the EGR valve.