Turbocharging Inspection & Service One of the best performance indicators of an engine is the boost pressure from the turbocharger. If the engine fuel system, air inlet system, injectors, engine adjustments and turbocharger are in good condition the engine will have no problem achieving maximum boost pressure when under load. If any of the above systems is defective or misadjusted, maximum boost pressure will not be achieved. A quick route to evaluating whether a low power complaint is legitimate is to evaluate the turbo boost. Turbo boost is always measured at peak torque when the engine is under load. Peak torque on most applications occurs between 55-70% of rated speed. More commonly, peak torque is at 2/3rds of rated RPM. Without a dynamometer to evaluate the engine, one can load the engine by moving the vehicle up a grade at full throttle or slightly lugging the vehicle using a gear above the one appropriate to the load.

Air Fuel Controls & Turbos It is important to remember that turbocharged engines use an air-fuel-ratio control device to limit particulate emissions. These are controls developed to limit the amount of fuel delivered to the combustion chamber until enough air is there to support combustion. A fuel system will inject the quantity desired by an operator instantly when accelerating the engine. Since turbochargers have an inherent lag time and air has inertia the fuel gets into the combustion chamber before the air. Most AFCs operate to modulate the fuel delivery proportional to the boost pressure. Given this arrangement, AFCs always slightly overfuel the engine in order to have the engine accelerate and to cause the turbo to spool or wind-up. Misadjusted AFCs can actually prevent the engine from accelerating by not providing a sufficient quantity of excess fuel to spool the turbo and accelerate the engine. Leaking control lines, gaskets etc.. causing leaks in the circuit connecting the AFC and the intake manifold can lead to low power complaints as well.

Two AFC controls Above Cummins PT. Adjacent Bosch RQV on P71000 pump

Turbocharger Inspection

Causes for Excess Wetness of A Turbocharger Include: y Excessive idle y Engine Oil Injestion (Air Compressor Intake) y High Crankcase pressure y Dirty Air Cleaner y Restricted Turbo Drain y Sudden drop in compressor inlet pressure Blown discharge hose, ATAAC hose,

Turbocharging Inspection & Service