Ok - I've edited* this, excerpted from various CRD manuals, in content and syntax, for clarity. Will be upgraded to include any further reliable data that may be posted to this or other forums
FUEL SYSTEM
- DESCRIPTION
The fuel system on the VM 2.8L Common Rail Diesel Engine uses a BOSCH rotary mechanical fuel injection pump and 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 valve
- Quick-connect fittings
- Water sensor\drain module
There is no auxiliary electric lift pump, though specific circuitry is factory-supplied in the wiring harness - ECM is programmed with appropriate logic functions required to drive a lift pump, if owner-installed
- FUEL INJECTION PUMP
The Jeep VM 2.8L CRD uses the Bosch CP3a injection pump - the CP3 is used also on the Cummins 5.9L I-6 CRD and the ISUZU\GM DuraMax 6.6L V8 CRD
DESCRIPTION
A radial 3-piston pump, with a medium-pressure gear-type fuel lift-pump attached to the back, is used as the high-pressure pump for common-rail fuel pressure generation - in this system it is capable of pressures between 300-1600 bar (4351-23206 psia) Note: 1Bar = 1 atmosphere, or 14.73psia
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 2/3 ratio to the crankshaft.
Fuel pressure is generated independently of the injection process.
A fuel quantity solenoid valve regulates injection pressure
The pump is lubricated by the pumped Diesel fuel and is not responsible for fuel injection timing.
The CP3 and drive gear is indexed such that it can be timed to coordinate pumping pulses with injection events **
OPERATION
- LIFT PUMP
DESCRIPTION
The gear-type pump has two functions
- draws fuel from the fuel tank in this application
- increases fuel pressure for regulation to housing pressure required for internal lubrication and supplying the high-pressure injection pump
OPERATION
Instead of using an external fuel supply lift-pump, this fuel system uses a supply-pump attached to the rear of the high-pressure pump body. This fuel lift-pump is driven by the end of the high-pressure pump shaft, and can generate over 20" vacuum at the fuel inlet at high rpm.
The lift pump draws fuel from the fuel tank through the fuel manager\filter.
The outlet of the lift pump provides pressurized fuel to a branched circuit internal to the high-pressure
pump flange, which supplies both the Fuel Quantity Solenoid valve and the Cascade Overflow Valve\regulator. Because the gear-pump increases fuel flow and pressure as engine rpm increases, pressure and flow is regulated by the COV.
The COV and supply-pump are not serviced independently of the high-pressure pump.
- CASCADE OVERFLOW VALVE
DESCRIPTION
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 Quantity 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 2.8L CRD requires 5bar (73psia)
For comparison, the 5.9L 6-cyl Cummins CRD requires 12.41bar (180psia)
OPERATION
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 (44psia), 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 3bar (44psia), but is less than 5bar (73psia), 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 5bar (73psia), 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 5bar (73psia).
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
- FUEL QUANTITY SOLENOID
DESCRIPTION
The Fuel Quantity 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 FQS valve control when CPS signal and rail pressure are within acceptable limits
OPERATION
The Fuel Quantity 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 FQS valve is commanded open by the ECM to allow the high-pressure pump to build maximum pressure (1600bar, 23,206psia), or closed to decrease pressure.
Thus, rail fuel-pressure can be increased or decreased independent of engine speed
The valve also has a fuel tank heat-protection function* that meters the exact amount of low-pressure fuel to the high-pressure pump to prevent excessive injector-heated fuel from returning to the fuel tank.
Temperature of fuel from the fuel tank is measured at the fuel inlet in fuel manager head via a temperature probe in the inlet side of the fuel-heater module.
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 (4351psia) and 1600bar (23,206psia) through a steel line to the fuel rail.
The pump is driven at 2/3 engine speed and is not responsible for injection timing.
CP3 function is to provide fuel at high-pressure, while the ECM controls injection pressure and timing.
The CP3 shaft is keyed to the drive gear and indexed such that timing can be set to coordinate the pressure waves of the pumping pulses with injection events **
- FUEL RAIL
DESCRIPTION
The fuel rail is 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.
OPERATION
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.
- FUEL PRESSURE SOLENOID
DESCRIPTION
The Fuel Pressure Solenoid valve is screwed into the rear of the fuel rail. The solenoid controls and maintains constant rail pressure by a pulse-width modulated 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 (23206psia).
OPERATION
In de-energized state, the FPS valve is closed as spring tension forces the ball into the
ball-seat - spring tension limits minimum rail pressure to 100 Bar 1445psi. When the engine is started, the solenoid valve is additionally held closed by electro-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 excess 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.
- FUEL LINES
DESCRIPTION
LOW-PRESSURE FUEL LINES
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
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.
OPERATION - HIGH PRESSURE FUEL LINES
High-pressure fuel lines deliver fuel under extremely high pressure - between 300-1600 bar (4351-23206 psia) - from the high-pressure pump to the rail 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.
- FUEL MANAGER\FILTER
FUEL FILTER / WATER SEPARATOR
DESCRIPTION
The fuel filter/water separator assembly is located in the left rear corner of the engine compartment. It incorporates the fuel system prime-button, bleed screw, fuel temperature sensor, fuel heater and a Water-In-Fuel (WIF) sensor.
The fuel filter has a 3-micron element and installs with right-hand threads.
Only the fuel filter cannister and the WIF sensor are serviced separately.
OPERATION
The fuel filter/water separator protects the high pressure fuel injection pump by removing water and contaminantsfrom 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 attached between the fuel manager head assembly and the filter - it is not serviced separately from the head.
- WATER IN FUEL SENSOR
DESCRIPTION
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.
It is removed for installation on the replacement fuel filter cannister
OPERATION
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
- FUEL HEATER
DESCRIPTION
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 attached to the fuel manager head, between the head and the fuel filter cannister.
On temperature is 7°C (45° F), off temperature is 29°C (85° F).
OPERATION
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
- FUEL TEMPERATURE SENSOR
DESCRIPTION
The fuel temperature sensor is integrated into the fuel heater module, on the inlet side of the fuel head. The sensor is used to detect the temperature of incoming fuel and is measured by the ECM. The sensor ranges from - 40°C (-40°F) to 140°C (284°F). If the engine is cold, the actual value will be ambient temperature. The temperature value rises after the engine has been started and warm fuel is returning to the fuel tank.
The fuel temperature sensor is not serviced separately from the fuel heater assembly.
OPERATION
A negative temperature coefficient (NTC) resistor integrated in the fuel temperature sensor alters it’s electrical resistance as fuel temperature changes(the resistance drops as the temperature rises). The ECM uses this reading to calculate optimum engine performance under all driving conditions. If the fuel is too warm, rail system volume will be lowered.
*The fuel quantity solenoid reduces flow to the fuel rail, excess heated overflow return is reduced and fuel temperature is lowered.
- NON-OPTIONAL ELECTRIC FUEL LIFT PUMP
ELECTRIC LIFT PUMP
Circuitry is supplied for an auxilliary electric fuel pump - this is not a factory option, but may be installed by the owner
Note - DCJ offers an oem fuel lift pump module with correct 8.5-14psig output pressure, from the Dodge Ram Cummins vehicle line, which is identical to the pumpless fuel module in the KJ fuel tank, and is directly replaceable - this may be installed by dropping the fuel tank and adding a short extension to the rear harness - following installation procedures are from the CRD TECH ONLY section on this Board:
viewtopic.php?f=98&t=37868Aftermarket installations can also be found in that section
DESCRIPTION
NOTE - official description is not provided by DCJ - the following desc is based on observed functional operation in this chassis along with standard ECU-control of electric fuel lift pumps in DCJ and other Diesel systems
The under-hood Fuse Center contains a fuse and relay for an electric lift pump.
Relayed power wiring is supplied in the vehicle wiring harness for mounting the pump in or near the fuel tank
OPERATION
Fused power to the relay is supplied when the IGN switch is in the ON position.
ECM controls the relay in two modes, prime and run - a safety feature helps prevent fire in event of accident or other emergency
At power-ON, during WTS, ECM closes the relay to prime the low-pressure fuel system to the Inj Pump - if ECM does not sense pulses from the Crank Position Sensor within 15 seconds, the relay is powered down - relay is powered up again when CPS senses crankshaft rotation, indicating START in progress
Power is maintained until crankshaft stops, which is a saftey feature, or when IGN is switched OFF
NOTE: Unofficially, contract engineering has indicated aux lift pump pressure of only 5psi has resulted in excessively rich fuel\air ratios in the DCJ Jeep CRD R&D Lab, resulting in black smoke and rough running - it was further stated that the engine resumed normal operation after aux pump was removed and fuel supply line was reconnected in oem configuration
Further owner-experience after addition of DCJ oem in-tank lift pump at 8.5-14psig fuel pressure indicates this does not happen, but rather improves overall engine operation during starting and running
NOTE: proceed with caution when installing an aux pump - pressures ~5-9psig and flow rates ~30gph appear to work best in street installations - bigger is not better, here.
- FUEL RETURN-LINE COOLER
Because of the compact fuel system in the Liberty CRD, an air-over cooler should be installed in the fuel-return line.
Return fuel is that fuel which is in excess of all injection events - this fuel can be at engine coolant temperature and higher as it leaves the injectors and mixes with excess fuel being returned from the Inj Pump.
The oem return line in the short-wheelbase KJ does not provide enough surface area required for proper fuel cooling to reduce these high temperatures prior to re-entering the fuel tank.
Fuel aeration increases as Diesel fuel temperature increases - in-tank fuel temperature increases even more rapidly as fuel level drops, thus making the Jeep Liberty CRD a prime candidate for an auxilliary fuel cooler.
Bosch indictates an in-line return-fuel cooler is necessary in some CRD systems.
The CP3 system in the 6.6L DMax is factory-equipped with a fan-over return-line cooler to prevent fuel cut-back as in-tank temperature rises.
Several configurations are available, with the 12v fan-cooled type being the most compact while providing sufficient cooling area
Thermostatically-controlled valves are available to bypass the cooler in winter climes
*ongoing
** Corrected CP3a timing information can be found in this thread:
viewtopic.php?f=5&t=58007Thanks to all contributors, past, present, and future, on this board and others - but not to DCJ, for the misinformation in their (dis)service manuals........................
END (projected)_________________________________________________
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I'd say it's a bit buggy in the firmware.
BTW: I posted this at 1:32a, EST.
