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Discussion Starter #1 (Edited)
I've edited excerpts from the manual for clarity and scope - read it if you will, ignore it if you must.......................

A Robert Bosch high-pressure fuel injection pump is used.

The fuel system on the 6.6L Common Rail Diesel Engine uses a rotary mechanical fuel injection pump and an Electronic Control Module (ECM) and is a drive-by-wire system, meaning there is no physical throttle cable.
The fuel delivery system consists of the:
- Accelerator pedal position-sensor module
- Air cleaner housing\element
- Fuel filter\water separator
- Fuel temperature sensor
- Fuel heater
- Fuel rail solenoid
- Fuel rail pressure sensor
- Fuel injection pump
- Fuel injectors
- Fuel tank
- Fuel tank filler\vent tube assembly
- Fuel tank filler-tube cap
- Fuel tank module containing the roll-over valve and a fuel gauge sending unit (fuel level sensor).
- Fuel tubing\lines\hoses
- High-pressure fuel injector lines
- Low-pressure fuel supply and return lines
- Low-pressure fuel return line
- Overflow valve
- Quantity control Fuel Control Actuator valve
- Quick-connect fittings
- Water sensor\drain module

The DMax 6.6L V8 CRD uses the Bosch CP3 injection pump, used also on the Cummins 5.9L CRD and the Jeep 2.8L CRD

A radial, 3-piston pump, with a gearotor-type fuel lift pump attached to the back cover, is used as the high-pressure pump for common-rail fuel pressure generation - it is capable of pressures between 300-1600 bar (4351-23206 psi) .
A spring-loaded Cascade Overflow Valve regulates internal housing pressure
Regulated internal housing pressure is oem-specific
The pump shaft is driven by the timing belt at 1:1 ratio to the crankshaft.
Fuel pressure is generated independently of the injection process.
A Fuel Control Actuator solenoid valve regulates injection pressure
The pump is lubricated by the pumped Diesel fuel and is not responsible for fuel injection timing.



The gearotor pump has two functions
- draws fuel from the fuel tank
- increases fuel pressure for regulation to housing pressure required for internal lubrication and supplying the high-pressure injection pump

This fuel system uses a gearotor supply-pump attached to the rear of the high-pressure pump. This medium-pressure fuel pump is driven by the end of the high-pressure pump shaft, and can generate 20" vacuum at the fuel inlet at high rpm.
The gearotor pump draws fuel from fuel tank through the fuel manager\filter.

The outlet of the gearotor pump provides pressurized fuel to a branched circuit internal to the high-pressure pump flange, which supplies both the Fuel Control Actuator solenoid valve and the Cascade Overflow Valve\regulator. Because the gearotor pump increases fuel flow and pressure as engine rpm increases, the pressure and flow is regulated by the COV.

The COV and gearotor supply-pump are not serviced independently of the high-pressure pump.


The COV is located on the front cover of the high pressure pump.
The Cascade Overflow Valve has three functions:
- regulation of lubrication fuel to the internal moving parts of the high-pressure pump
- regulation of the fuel pressure being supplied to the Fuel Control Actuator solenoid valve
- return excess fuel to the fuel tank
This regulated internal pressure is known as housing pressure, and is determined by engine displacement and power requirements

The COV has a spring-loaded center spool-piece that has a drilled channel with three passages: one for initial low-pressure lubrication, one for lubrication at housing-pressure , and one for overflow. The valve is operated in three stages based on the level of pressure at the inlet.

Stage 1
When the fuel pressure entering the tip of the COV is between 0 and 3 bar (43psi), pressure is too low to overcome regulator spring tension and fuel flows through the center channel, only . This passage always allows fuel flow through to the pump center-ring and lubricates the pump bushings and internal moving parts. This circuit also allows air to bleed during initial cranking and returns the air to the fuel tank.
The COV is in Stage 1 during cranking, only.

Stage 2
When the fuel entering the COV exceeds 5bar (80psi), but is less than 12.4bar (180psi), the spool-piece moves against spring tension aligning a second passage for lubrication purposes.
Stage 2 can be reached during cranking and initial start up.

Stage 3
When fuel pressure exceeds 12.4bar (180psi), the spool-piece aligns with the overflow passage. This stage relieves the pressure into an overflow circuit that sends the fuel back to the inlet side of the gearotor pump, thus limiting maximum fuel pressure to 12.4bar (180psi).
Lubrication fuel continues to flow through all channeled passages during this stage.
Excess fuel is sent back to the fuel tank through the fuel-return circuit
Stage 3 is reached at over-pressure


The Fuel Control Actuator solenoid valve is located on the back of the front cover of the high-pressure pump. The solenoid is pulse-width modulated by the ECM and meters the amount of fuel that flows into the high-pressure elements inside the high-pressure pump.
The solenoid is inactive up to 30 seconds after IGNition switch is initially keyed to ON position to allow maximum fuel pressure to the fuel rail during cranking and start up. ECM assumes FCA valve control when CPS signal and rail pressure are within acceptable limits

The Fuel Control Actuator solenoid valve is a pulse-width modulated valve that controls the amount of fuel sent or delayed to the high-pressure pump elements inside the high-pressure pump. The ECM determines the fuel pressure set point based on engine sensor and rail-pressure inputs. If the actual fuel-rail pressure is too low, the ECM commands the solenoid to allow more fuel to flow to the high-pressure pump. This minimizes the difference between the actual fuel-rail pressure reading and the set point. The ECM will also operate the solenoid to delay fuel, reducing flow-rate, if the fuel-rail pressure becomes too high.
The FCA valve is commanded open by the ECM to allow the high-pressure pump to build maximum pressure
(1600bar, 23,206psi).
Thus, rail fuel-pressure can be increased or decreased independent of engine speed

High Pressure Pumping Plungers
The FQS valve supplies three high pressure pumping chambers. The pumping chambers have one-way inlet valves that allow fuel to flow into the chambers. The valves then close as the fuel is compressed, causing the high pressure fuel to overcome a spring-loaded ball-and-seat outlet valve.
All three pumping chambers are tied together in one circuit internal to the pump and provide high pressure fuel between 300bar (4351psi) and 1600bar (23,206psi) through a steel line to the fuel rail.
The pump is driven at 1:1 engine speed and is not responsible for injection timing.
Pump function is to provide fuel at high-pressure, while the ECM controls injection pressure and timing.


The fuel rails are mounted to the cylinder-head cover\intake manifold. The rail distributes regulated high-pressure fuel equally to the fuel injectors.
A pressure sensor is screwed into the rail so ECM can read and regulate system pressure.
A pressure solenoid is screwed into the rear of the fuel rail to allow regulated overflow return to the fuel tank.

The fuel rail stores the fuel for the injectors at high pressure. At the same time, the pressure oscillations which are generated due to the high-pressure pump delivery and the injection of fuel are dampened by rail volume.
The fuel rail is common to all cylinders, hence it’s name "common rail". Even when large quantities of fuel are extracted, the fuel rail maintains a constant inner pressure. This ensures that injection pressure remains constant from the instant the injector opens to the end of the injection event.


The Fuel Pressure Solenoid valve is screwed into the rear of the fuel rail. The solenoid controls and maintains constant rail pressure by a control current transmitted by the (ECM).

The tip-end of the FPS uses a knife-edge type high-pressure seal. The knife edge actually deforms the metal in the fuel rail in order to seal the surfaces.
The FPS must be replaced if it is removed from the rail - each replacement must establish the knife-edge seal to prevent leaks at 1600bar (23000psi).

In de-energized state, the FPS valve is closed as spring tension forces the ball into the
ball-seat. When the engine is started, the solenoid valve is held closed by magnetic force. When running, fuel pressure counteracts the magnetic force of the coil and spring tension, opening the valve . When the engine is running, the valve is always open to a varying degree, controlled by the ECM.

The ECM senses operating fuel pressure by the rail pressure sensor signal.

High pressure fuel in the rail flows to the ball-seat of the solenoid valve. The specified
rail pressure required by the system is set by the FPS - the ECM sends a controlled current thru the solenoid, building up a magnetic force which corresponds to this specific pressure. This magnetic force equals a specific cross-sectional outlet at the ball-seat of the valve, which allows fuel to flow through.

Rail pressure is altered as a result of the controlled quantity of fuel which flows off.

Controlled excess fuel flows back through the return-fuel line, into the tank.

By reducing fuel at the inlet to the high-pressure pump with the FQS valve, which reduces excess fuel through FPS valve without reducing rail pressure, ECM can control in-tank fuel temperature.



All fuel lines up to the fuel injection pump are considered low-pressure. This includes the fuel lines from the fuel tank module to the inlet of the high-pressure fuel injection pump. The fuel-return lines and the fuel-drain lines are also considered low-pressure lines.
High-pressure lines are used between the fuel injection pump and the fuel injectors

High-pressure fuel lines are used between the high pressure fuel injection pump and the fuel rail, and between the fuel rail and fuel injectors
All other fuel lines are considered low-pressure lines.

High-pressure fuel lines deliver fuel under extremely high pressure - between 300-1600 bar (4351-23206 psi) - from the high-pressure pump to the rails to the fuel injectors. The lines expand and contract from the high-pressure fuel pulses generated during the injection process, which can delay the injection event - ECM compensates for that based on component specs
All high-pressure fuel lines between the rail and the injectors are of the same length and inside diameter to ensure equal-duration injection events, cylinder to cylinder.
Correct high-pressure fuel line usage and installation is critical to smooth engine operation.



The fuel filter/water separator assembly is located on the engine. It incorporates
the fuel temperature sensor, fuel heater and a Water-In-Fuel (WIF) sensor.
Only the fuel filter cannister and the WIF sensor are serviced separately. The top-loaded fuel filter has a 3-micron element and the cap tightens clockwise to the housing.

The fuel filter/water separator protects the high pressure fuel injection pump by removing water and contaminants from the fuel with a 3-micron filter element. The construction of the filter/separator allows fuel to pass through it, but helps prevent moisture (water) from doing so. Moisture collects at the bottom of the cannister for draining.

A Water-In-Fuel (WIF) sensor is attached to the fuel filter cannister and is serviced separately.

The fuel heater and fuel temperature sensor are in a thermoplastic module inside the fuel manager head - it is not serviced separately from the head.


The WIF sensor is attached to the bottom of the fuel filter/water separator cannister. The sensor also has a drain channel and provision for adapting a drain hose.
The sensor varies an input to the ECM, allowing it to sense water in the fuel filter/water separator.
As the water content in the filter/separator increases, the resistance across the WIF sensor decreases. This decrease in resistance is measured by the ECM and compared to a calibrated standard value. If the resistance drops to a value between 30 and 40 kohms, the ECM will activate the Water-In-Fuel warning lamp. This all occurs when the IGNition key is initially switched to ON position


The fuel heater is used to prevent diesel fuel from waxing and plugging the fuel filter during cold weather operation.
The fuel heater is located in the fuel heater module, next to the fuel temperature sensor - the module is internal to the fuel manager head.
On temperature is 7°C (45° F), off temperature is 29°C (85° F).

The element inside the heater assembly is made of a Positive Temperature Coefficient (PTC) material, and has power applied to it by the fuel heater relay anytime the ignition key is in the ON position. PTC material has a high resistance to current flow when its temperature is high, which means that it will not generate heat when the temperature is above a certain value. When the temperature is below 7°C (45° F), the resistance of the PTC element
is lowered, and allows current to flow through the fuel heater element warming the fuel. When the temperature is above 29°C (85° F), the PTC element’s resistance rises, and current flow through the heater element stops .

Fused voltage to operate the fuel heater is supplied from the Ign switch, through the fuel heater relay, when the ECM senses the IGNition (key) switch is ON.

Sensed temperature for on and off operation is the temperature of the element, which allows full heating only when the temperature drops below 7°C (45° F) - element should not produce full heat on an 18.3°C (65° F) day, for example
  • Like
Reactions: joebaum

6,573 Posts
Good reading, and I especially like the pink line in your Sig, if only more folks would try..........
  • Like
Reactions: stevewaclo

727 Posts
WOW I read that whole artical what a great amount of info!

6,945 Posts
Discussion Starter #4 (Edited)
This is from all the data I have been able to find, ex-manual - if anyone has the Factory Service Manual on CD and could shoot me the paragraph(s) on the DMax CP3 injection Pump system, I can cleanup and finalize this as far as GM-specific nomenclature, pressures, rail, and low pressure data - tia


16 Posts
I read all of this post and I had no idea that there was so much envolved in the fuel svstem great job.

1,308 Posts

371 Posts
This is exactly the type of information and formate, I look forward to, and enjoy reading in a diesel post.

good luck
drive safe
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