I found the white paper on the CP4 from Green Diesel Engineering;
Insight on CP4 Bosch fuel pump
The CP4 Bosch fuel pump has been in the field since 2008 model year with European OEMs in both 1-
plunger (CP4.1) and 2-pluger (CP4.2) configurations. It came to the US market in the 2011 model year
used by the North American OEMs. Over the years there have been many failures of this pump due to
the plunger rotating in the bore leading to the roller bearing grinding on the cam lobe and sending metal
throughout the system. The design of the roller-bearing and cam lobe create inertial force on the
plunger to keep it in the proper alignment and it should never rotate if the roller wheel and cam always
stay in contact. However, there are situations internal to the pump when there is not enough
downforce on the plunger to keep it in contact with the cam lobe. This is the core issue of why these
pumps can fail.
Now, let’s discuss the internal operation of the pump. There are three operating modes: MPROP
control, PCV control (bleed valve on high pressure fuel rail) and coupled pressure control (CPC). The
MPROP is Bosch’s name for the fuel metering inlet valve, this controls how much fuel is delivered to the
plunger chamber. During MPROP closed loop control, the PCV is over-closed and MPROP delivers the
proper fueling to achieve desired pressure in the fuel rails. This method has been used since 2001 on
the CP3 pump and is robust. When the accelerator is released the MPROP closes to decrease flow and
the PCV opens momentarily to relieve excess rail pressure as the requested pressure is decreased.
The next mode of operation is PCV control. Here the MPROP is fully open and delivering max fuel to the
pump plunger and the PCV regulates the fuel rail pressure in closed loop control by closing only enough
to reach the desired rail pressure. The downside to this mode is that the high volume of fuel that is
pumped into the rail and then recirculated out thru the PCV consumes a lot of power inside the pump
and also generates a higher amount of heat. OEMs generally use the PCV-only control method when fuel
temps are cold, in order to heat up the fuel faster. This control strategy is also employed on the CP3 and
CP1/CP1H pumps.
On high power-density small displacement applications it is necessary to size the high-pressure pump to
meet the fuel flow requirements at rated power. On applications with solenoid injectors there is an
additional margin that must be included, due to the constant leakage from the injectors thru the
backflow line. However, these small displacement engines have a very low fuel rate at idle which means
just a very small flow of fuel thru the metering unit given that the fuel rate is low and also the rail
pressure is at its lowest point when idling.
With consideration given to component tolerance, sometimes it is not possible to govern properly via
metering-unit only control the rail pressure at idle or when coasting with a max tolerance part. This
happens because the metering unit at its very first opening position flows more fuel than is necessary to
meet the required demand. In the days of the Bosch EDC16 controller several OEMs would make a
switch back to the PCV mode at very low fuel rates including coasting, to let the metering unit be open
into a more controllable area.
With the EDC17 era was possible also a new mode called CPC (Coupled Pressure Control). This mode
allows to prescribe a desired value for both the metering unit flow and also the rail pressure controlled
via the PCV valve, leading both actuators to be under closed loop control via PID-governors (proportial,
integral, and derivative components). The purpose of this is to allow the metering unit to operate in a
more controllable flow rate but not pay the penalty of power consumption and heat rejection by full
PCV mode. You can think of this mode as the PCV one but with lower flow rate thru the metering unit.
The OE calibrations for the EcoDiesel 2014 thru the present (both Gen2 and Gen3) all use this CPC mode
as part of their calibration strategy. If you rev the engine while parked with the hood open, as the
engine speed comes back to idle is very common to hear a prominent noise akin to gravel in a rock
crusher or to an engine with solid lifter camshaft that has an incorrect valve lash. This noise happens as
the metering unit flow is varied (via CPC algorithm) thru the pump and generally lasts for a number of
seconds, sometimes going away and other times persisting indefinitely.
We surmise that during this transition period of flow rate that the noise is generated by a clearance that
forms between the roller wheel and the pump’s camshaft. During normal operation (with the factory
calibration), the pump operates in MPROP mode generally when under load but constant makes the
transition to the CPC mode in light load and coasting situations. During that transition the MPROP has to
make a large change in delivery almost instantaneously, leading to a loss of motion control within the
valvetrain of the pump.
In all Green Diesel Engineering tuning we turn off CPC mode for EcoDiesel applications (GEN2 and
GEN3). This seems to have significantly reduced potential for the plunger to lift off the cam lobe. Due
to a persistent backflow from the solenoid injectors to the tank we find it is not necessary to use the
PCV mode for fuel heating. Thanks to additional learning functions inside the software we find it is 100%
reliable to run in metering-unit only control in 100% of operation. This eliminates the pump noise you
hear in light/no-load transitory operation and offers the least amount of energy to drive pump which
aids in fuel economy. Minimizing pressure disturbances internally in CP4 is the best method to
maximize fuel pump life and minimize a catastrophic failure.
GDE tunes exhibit a much lower failure rate in the field. The only failures of the fuel system we have
heard about entail putting gasoline in the fuel tank, putting DEF in the fuel tank, high water content in
diesel fuel or running the system out of fuel (pump loses lubrication).
if the new HPFP they put on your truck is like the CP-3 on the Cummins its very reliable so ya have nothing to worry about, now go out an enjoy your truck.....
