Ford Power Stroke 7.3/6.0/6.4 engine controls.June 29, 2018
When Ford in conjunction with International converted the 7.3L IDI engine from mechanical to the HEUI (Hydraulically Actuated Electronically Controlled Unit Injector) injection design, the Power Stroke brand was created. It was the first electronically controlled diesel engine in the light-duty market segment.
Over the years the 7.3L was replaced with the 6.0L engine and then in 2008, the twin turbocharged 6.4L design debuted. Today, the three different Detroit brands of light-duty diesel engines all use electronic controls and, in some way have a little of the original Power Stroke’s DNA in them.
Realizing the popularity of the Power Stroke engine with farmers, I wanted to create a primer that provided an over view of the electronics under the hood of your older Ford. Not meant to replace the factory shop manual when it comes to repair or diagnostics, but instead to supplement it. Most shop manuals are very good at providing diagnostic steps along with remove and replace procedure but offer little to understand the sensors used on the engine and the control logic involved. Thus, this article will be focused on becoming familiar with the sensors used on the 7.3L, 6.0L and 6.4L Ford engine. Due to different emission control standards the three versions of the Power Stroke do not use every sensor that will be represented. Always reference the appropriate shop manual for the system that your engine has.
The Power Stroke prior to the 6.4L model employed a fuel system that was different from the IDI version of the engine. The HEUI technology was actually developed by the Caterpillar Engine Division in Pontiac, Illinois. It was the result of a joint venture between Caterpillar and International Truck. The system debuted on the International 7.3L engine. It was known as the 444E by International and the Power Stroke when installed in a Ford.
A major advantage of the HEUI design was that it offers significant control over the injection rate and duration when compared to a conventional mechanical system. HEUI injectors are actuated by engine oil pressure. The electronics that manage the HEUI fueling controls the actuation oil pressure over a very wide range of values. This results in precise control of injected fuel pressure entirely independent of engine speed. With a mechanical fuel delivery system, the fuel was usually supplied by an actuator lever riding on the camshaft, so engine speed would control the fuel pressure produced. The rate-shaping ability of the HEUI design provided much greater tuning of the fuel delivery on a diesel engine than anything else available in North America in 1994.
The early Power Stroke used a Caterpillar produced HEUI injector but when the 6.0L engine came out, its HEUI system (injectors) were produced by Siemens with a Bosch-built high-pressure oil pump.
Heavy-duty Caterpillar engines that feature the ACERT system (Advanced Combustion Emissions Reduction Technology) use the HEUI injector design.
The 6.4L Power Stroke eliminated the HEUI system and went to a common rail piezo injector that used no engine oil. The system is similar to what would be found on an EFI gasoline engine.
The heart of the injector is the piezo actuator. It is an electrically energized device that acts similar to a solenoid but is much more precise. It is comprised of piezo disks that when electrically charged, causes them to deform that results in an expansion. This expansion creates a longitudinal motion that controls the injection of fuel. When energized, the piezo actuator pushes downward against the valve piston (in the injector). The piezo actuator is then returned to its non-energized state via the electronic controller switching the polarity of the electrical feed to the injector.
Due to its speed, the piezo injector can produce up to 5 injection cycles per combustion event. This greatly reduces exhaust emissions and is able to control the cylinder pressure rise for less noise. The piezo actuator is turned on for only approximately 400 millionth of a second to create two injections.
Even though the 7.3/6.0L and 6.4L Power Stroke do not share a basic fuel deliver system design, they rely on electronics to control the amount of diesel fuel injected into the combustion chamber. The Power Strokes are direct injection engines so no pre-chamber exists in the cylinder head. The compression ratio is lower than an IDI design (The pre-chamber greatly increases the surface volume and thus, the thermal loss into the coolant.) and all use a microprocessor to make the fuel delivery and timing decisions. But the similarity ends there. The 7.3/6.0L employs two microprocessors to operate the injectors while the 6.4L has one unit. The 7.3L Power Stroke used a PCM in conjunction with an IDM (Injector Driver Module) instead of the 6.0L FICM. The IDM employed an internal DC to AC converter that boosted the signal to the injectors to 115 volts.
The 6.0L engine uses two computers in series to control the engine. There is a PCM (Power Train Control Module) and a FICM (Fuel Injection Control Module). The two modules are intrinsically linked since both have a flash memory and are involved with the decision-making process of how long and when to open the fuel injector. The majority of the authority for the engine calibration is in the PCM while the FICM does the actual work of opening the injectors through an electronic device called a driver. This can be considered a high current switch that has no moving parts. The FICM also internally generates the 48 volts that the HEUI system on the 6.0L uses.
In the FICM, each each individual injector is controlled with four driver inputs. There are high and low side drivers for the open and close coil of each injector. On later 6.0L engines, the low side driver is actually shared among four injectors. This means an injector short to ground on the low side could produce four different cylinder error codes. The first (2003) engines had an individual low side driver for each injector.
Unlike a gasoline fuel injector, the Power Stroke HEUI system requires both an open and and close command for the injection cycle. In contrast, a gasoline engine uses only an open command and when shut off, the internal spring closes the injector. The high operating pressure of the HEUI will not allow for that. It needs to be remembered that the FICM and or IDM (7.3L) is actually controlling the high-pressure engine oil on the top of the injector to provide fuel delivery. The PCM and FICM communicate through what is known as a CAN (Controller Area Network) circuit.
When the 6.4L was introduced the FICM was eliminated and the injector control drivers were now in not a PCM but an ECM (Engine Control Module). The piezo design uses a varying command from 42 to 96 volts DC. The necessary voltage is created in the ECM.
In summation, the first Power Stroke (7.3L) employed a HEUI injector that operated with 115 volts and was controlled through a combination of a PCM and IDM. The 6.0L version had a HEUI design with Siemens instead of Caterpillar injectors and was run via a FICM and PCM on 48 volts. The 6.4L eliminated the HEUI system and replaced it with a common rail, piezo injector operating with between 42 and 96 volts though only the ECM.
Regardless of the style of fuel delivery, for the PCM/ECM to determine the requirements of the engine, sensors are needed. A sensor is a device that translates a physical state or condition into an electrical signal.
In all applications the PCM/ECM uses a 5-volt reference signal for most if not all sensors. This is a common logic employed among controllers for both gasoline and diesel engines. The sensor produces an output voltage that is then sent to the PCM/ECM. This is used to decide fuel delivery.
Due to the stricter control on emissions with every passing year, the 6.4L Power Stroke has more sensors than any previous version. It is also responsible to control the burn-off regeneration of the diesel particulate filter (DPF), so additional data is required that an earlier system did not need. The following are common Power Stroke sensors but may not be used in all applications:
AP (Accelerator Pedal position)
The AP incorporates three potentiometers to track throttle position. Throughout the movement of the AP the resistance values of the three potentiometers must agree. If not, the Check Engine light will illuminate and the vehicle will continue to perform as normal. If two signals from the AP are lost, the ECM will allow the engine to idle only and the CE light will be on.
Baro sensor (Barometric pressure)
A 5-volt reference signal is supplied to the Baro sensor and it produces an analog output signal. The 6.4L has the sensor located in the ECM while the earlier engines use a remote sensor. The primary function of the Baro sensor is to provide altitude information so that the timing, fuel quantity, glow plug on time and turbocharger boost can be altered.
CKP (Crankshaft Position)
The CKP signal is created by a magnetic pick-up sensor mounted to the front of the engine block. It reacts to a trigger wheel positioned on the crankshaft. The sensor produces a sine wave that is converted by the ECM/PCM to a digital signal. Crankshaft speed is determined by the frequency of the signal output.
CMP (Camshaft Position)
The CMP sensor signal is the result of a magnetic pick-up mounted on the engine block. The sensor reacts to a trigger placed on the camshaft. Camshaft position is used in conjunctions with the CKP to calculate engine firing position.
ECT (Engine Coolant Temperature)
The ECT is a thermistor which is the opposite of a resistor. As it is heated its resistance drops. It is used for fuel delivery modification based on the engine temperature.
EGRVP (EGR Valve Position)
The EGRVP is a three-wire potentiometer. The engine controller uses the EGRVP sensor to tailor the amount of recirculated exhaust gas based upon engine operating conditions.
EOT (Engine Oil Temperature)
It is a two-wire sensor similar to the ECT. The ECM/PCM monitors engine oil temperature to aid in controlling fuel rail pressure and fan control. This allows the engine controller to compensate for oil viscosity variations due to temperature changes and ensure adequate engine power is produced for all operating conditions.
IAT1 (Intake Air Temperature #1)
This sensor is a two-wire thermistor that is located inside the mass air flow sensor. It primary function is to measure intake air temperature to aid in controlling the variable vane turbocharger and the glow plug system.
IAT2 (Intake Air Temperature #2)
Also, a thermistor but it looks different than IAT1. Its function is to monitor the air temperature in the intake manifold.
FRP (Fuel Rail Pressure)
This is a three-wire variable capacitance sensor. Its function is to provide data to the controller indicating the pressure in the fuel rail. The ECM/PCM monitors the FRP as the engine is operating to modulate the pressure control valve. It is also used to command the proper injection timing.
MAF (Mass Air Flow)
It uses a hot wire sensing element to measure the amount of incoming air to the engine. The air flow cools the sensing wire and the current required to keep it at 392 degrees F above the IAT1 temperature is then measured.
MAP (Manifold Absolute Pressure)
A three-wire variable capacitance sensor is used to assist in the calculation of EGR control, fuel delivery and throttle body position along with boost pressure.
EP (Exhaust Pressure)
Also, a three-wire design, it measures the exhaust back pressure for EGR and high-pressure turbocharger control.
FTS (Fuel Temperature Sensor)
A two-wire thermistor, its output is tailored to the fuel temperature. It is used to control fuel delivery.
EGRT Outlet (EGR Cooler Outlet Temperature)
A two-wire thermistor. The engine controller monitors exhaust temperature with this sensor to aid in controlling both the EGR valve and throttle plate position.
Maintenance is the key
HEUI equipped Power Stroke engines are very susceptible to poor injector performance caused by extended engine oil drain intervals, improper oil, and low-quality fuel. Unlike a mechanical injector, the HEUI cannot be taken apart for cleaning and service by a diesel shop. If it fails it must be replaced. Remanufactured HEUI injectors are offered and are quite costly. It is much less expensive to keep the engine oil changed and use a good quality fuel additive in the tank on every fill up.
The piezo injectors are not serviceable at this time and need to be replaced if there is a problem. Though engine oil does not affect piezo designs, good service procedure is the route for a long and trouble-free life of any engine.
In many ways the Power Stroke engine has received a black eye for reliability. Some of that may be justified but more is based on not understanding the system and simply replacing components that are not the cause of the problem and just the result of it. Hopefully, now you will have a better understanding of what is going on under the hood of your diesel Ford.