The collaborative efforts of Caterpillar and International introduced electronic fuel injection to the 7.3 Power Stroke. This engine relies on extremely high oil pressure to build fuel pressure within the fuel injector.
The 7.3 is a direct-injection fuel injection where the fuel is injected directly into the extreme pressures of the cylinder, thus the reason for the high fuel pressure to overcome these pressures.
The 7.3 Power Stroke uses a PCM (powertrain control module) in conjunction with the IDM (injector driver module) to operate the engine. The primary function of the IDM is to boost the DC (direct current) signal sufficiently to operate the fuel injector under such loads. The standard 12 volts would be insufficient in opening the pintle in the injector under these pressures, so the IDM increases the voltage to 115 volts.
The high voltage allows for much faster and accurate opening of the injector. Engine mods are available to further increase this voltage increasing the power and torque by 20 percent or better.
If the voltage drops through resistance in the harness or connector the vehicle will run, but poorly with a severe lack of power. In a failure of the IDM the engine will not start at all.
At this voltage the reaction time is significantly multiplied. The PCM, through various sensors detecting engine speed and load, controls the on and off time of the injectors. A grounding circuit does this for each injector within the computer. Essentially the computer supplies the ground that operates the injectors which has a constant supply of voltage with the key on.
The 6.0 Power stroke system is somewhat different in that it uses a PCM and a FICM (fuel injection control module) both of which are flash programmed. Under this system each injector is operated with the use of an open and a closed driver solenoid.
The PCM is the primary controller in the decision making as to the timing and length of injector pulse, while the FICM is in control of the injector drivers. Both the PCM and the FICM are intrinsically linked through the use of a “CAN.” When replacing either of the units it is necessary to flash them unless purchased from a location claiming to have already done so.
The IDM is located under the fenderwell on the passenger side of the truck. Should any driveability issues arise, access the IDM and check both the harness and the connector. They are prone to failure due to their location. Start the engine and wiggle the wires to the IDM while paying particular attention to engine speed. If the harness or connector is faulty, the engine will respond to the movement of the harness.
As a last word, to prevent problems down the road with a diesel engine, especially a Power Stroke-keep in mind that the injectors operate off oil pressure. The oil pump rests on the top rear of the engine behind the manifold and under the turbo.
It is prone to leaking which reduces the oil pressure and hence lowers the injector performance. A failed oil pump-which is common place-will cause a no start.
Always change the oil at the correct time (mileage) and with the proper grade only. Generally every 2000 miles is appropriate. Diesels will not go as far between oil changes due to engine blow by due to high compression leakage past the rings and valve guide and contaminating the oil. Once contaminated a whole bucket of worms is opened.