Quote:
Originally Posted by MadMan77
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I stand corrected. I didn't read through the whole thread and at the beginning it sounded like he was describing the one on the high pressure side. I'll REALLY be shocked if that low pressure sensor has anything to do with the failures we've been seeing. The ECU is capable of setting a completely seperate code for that being out of spec, but who knows. Those guys for sure aren't idiots so maybe they're on to something.
As a programmer I'm not sure why BMW would be concerned with the low pressure side, other than to make sure the pressure was sufficient, but maybe there's something strange going on in there.
For anyone who hasn't seen it, here's the technical info on how the HPFP works
(Starts on page 24)
http://www.1addicts.com/goodiesforyou/n54-2.pdf
High Precision Injection (HPI)
High-precision injection represents the key function in the concept for as economic a use of fuel as possible. The new generation of petrol direct injection satisfies the expectations placed on it with regard to economic efficiency without compromising on the engine's dynamic qualities.
High-precision injection provides for amore precise metering of mixture and higher compression - ideal preconditions for increasing efficiency and significantly reducing consumption. This is made possible by locating the piezo injector centrally between the valves. In this position, the new injector, which opens in an outward direction, distributes a particularly
uniform amount of tapered shaped fuel into the combustion chamber. The new direct injection of BMW HPI spark ignition engines operate according to the spray-directed process.
HPI Function
The fuel is delivered from the fuel tank by the electric fuel pump via the feed line (5) at an
“feed” pressure of 5 bar to the high pressure pump. The feed pressure is monitored by
the low-pressure sensor (6). The fuel is delivered by the electric fuel pump in line with
demand.
If this sensor fails, the electric fuel pump continues to run at 100% delivery with terminal
15 ON.
The high pressure pump is driven “in-tandem” with the vacuum pump which is driven by
the oil pump chain drive assembly.
The fuel is compressed in the permanently driven three-plunger high-pressure pump (8)
and delivery through the high-pressure line (9) to the rail (3). The fuel accumulated
under pressure in the rail in this way is distributed via the high-pressure lines (1) to the
piezo injectors (2).
The required fuel delivery pressure is determined by the engine-management system as
a function of engine load and engine speed. The pressure level reached is recorded by
the high-pressure sensor (4) and communicated to the engine control unit.
Control is effected by the fuel-supply control valve (7) by way of a setpoint/actual-value
adjustment of the rail pressure. Configuration of the pressure is geared towards best
possible consumption and smooth running of the N54 engine. 200 bar is required only
at high load and low engine speed.
Index Explanation Index Explanation
1
High-pressure line to injector (6) 6 Low-pressure sensor
2
Piezo injector 7 Fuel supply control valve
3
Fuel rail 8 Three pluger high pressure pump
4
High pressure sensor 9 High pressure line (pump to rail)
5 Feed line from in-tank pump
Index Explanation Index Explanation
1
Thermal compensator 8 Supply passage, pressure limiting valve
2
Low pressure non-return valve (check valve) 9 High pressure non-return valve (x 3)
3
Connection to engine management 10 Pendulum disc
4
Fuel supply control valve 11 Drive flange, high pressure pump
5
Return, pressure limiting valve 12 Plunger ( x 3)
6
Supply from electric fuel pump (in-tank) 13 Oil filling, high pressure pump
7 High pressure port to fuel rail 14 Fuel chamber ( x 3)
High Pressure Pump Function and Design
The fuel is delivered via the supply passage (6) at the admission pressure generated by
the electric fuel pump to the high-pressure pump. From there, the fuel is directed via the
fuelsupply control valve (4) and the low-pressure non-return valve (2) into the fuel chamber
(14) of the plunger-and-barrel assembly. The fuel is placed under pressure in this
plunger-and-barrel assembly and delivered via the high pressure non-return valve (9) to
the highpressure port (7).
The high-pressure pump is connected with the vacuum pump via the drive flange (11)
and is thus also driven by the chain drive, i.e. as soon as the engine is running, the three
plungers (12) are permanently set into up-and-down motion via the pendulum disc (10).
Fuel therefore continues to be pressurized for as long as new fuel is supplied to the
high-pressure pump via the fuel-supply control valve (4). The fuel-supply control valve is
activated by means of the engine management connection (3) and thereby admits the
quantity of fuel required.
Pressure control is effected via the fuel-supply control valve by opening and closing of the
fuel supply channel. The maximum pressure in the high-pressure area is limited to 245
bar. If excessive pressure is encountered, the high-pressure circuit is relieved by a
pressure-limiting valve via the ports (8 and 5) leading to the low-pressure area.
This is possible without any problems because of the incompressibility of the fuel, i.e. the
fuel does not change in volume in response to a change in pressure. The pressure peak
created is compensated for by the liquid volume in the low-pressure area.
Volume changes caused by temperature changes are compensated for by the thermal
compensator (1), which is connected with the pump oil filling.
Pressure Generation in High-pressure Pump
The plunger (2) driven by the pendulum disc presses
oil (red) into the metal diaphragm (1) on its upward
travel. The change in volume of the metal diaphragm
thereby reduces the available space in the fuel
chamber. The fuel thereby placed under pressure
(blue) is forced into the rail.
The fuel-supply control valve controls the fuel
pressure in the rail. It is activated by the engine
management system via a pulsewidth modulated
(PWM) signal.
Depending on the activation signal, a restrictor crosssection
of varying size is opened and the fuel-mass
flow required for the respective load point is set.
There is also the possibility of reducing the pressure
in the rail.
Limp-home Mode
If a fault is diagnosed in the system, such as e.g. failure of the high-pressure sensor, the
fuel-supply control valve is de-energized; the fuel then flows via a so-called bypass into
the rail.
In the event of HPI limp-home mode, turbocharging is deactivated by an opening of the
wastegate valves.
Causes of HPI limp-home mode can be:
• Implausible high-pressure sensor values
• Failure of the fuel-supply control valve
• Leakage in the high-pressure system
• Failure of the high-pressure pump
• Failure of the high-pressure sensor
There's some more info there, but it's a PITA to copy and past all the diagrams that go with it.