I have a 2014 r60 s all4 that is giving me a curious delima. I have been having difficulty starting after a short time stopped. Sounds like flooding as it tries to catch but keep turning over. Normally happens if sitting 10 to 20 minutes between turning off and trying to restart. Not throwwing any codes except a misfire but not often, looks to be a result of flooding but it doesnt come in nearly as often as the hard to start issue. Overnight starts and runs fine. A little hesitant on acceleration. Monitored the fuel pressure with protool and it runs 1000 psi at idle and 1700 at acceleration and higher rpms. All in specs according to tis. My conundrum is that when I turn the car off, the psi climbs. Just 5 psi slowly. When the car timed out the obd2, it was at 1500 psi. I know the hpfp runs off the intake cam. And I am getting a pressure reading from protool so the cpu sees a pressure reading which makes me think the sensor is good. What would tell the low pressure pump to stop or does it climb to a certain point after shutoff and i only have leaky injectors?

 

I assume TIS has a decent description of the fuel management system, but in case you don't have the R56 training literature, below is the text. I'm assuming the logic is the same for the N18 engine? Good luck!

Direct Injection N14
The direct injection system on the N14
engine features a low and a high pressure
fuel system. The low pressure system is
used to feed the mechanically driven high
pressure pump which is mounted on the
engine.
The low pressure system consists of an “intank”
electric fuel pump which is activated by
a relay which is ground controlled by the
ECM.
HDP Pump
The primary component on the high
pressure system is the high pressure (HDP)
fuel pump. The pump is driven by a
mechanical connection to the intake
camshaft.
The HDP pump contains 2 pistons to
generate the necessary pressure in the
fuel system. The maximum fuel delivery
pressure is 120 bar. There is a volume
control valve on the high-pressure pump.
The ECM is responsible for the activation
of the volume control valve.
Volume Control Valve
The volume control valve is connected by
means of a two wire circuit to the ECM.
It receives system voltage via the ECM
main relay.
The ECM drives the volume control valve
pulse-width modulated on the ground
side.
The required fuel delivery pressure is
determined by the engine-management
system as a function of engine load and
engine speed.
The pressure level is registered by the rail
pressure sensor and transferred to the
ECM.
The volume control valve controls the pressure by comparing the target/actual rail
pressure. The rail pressure is laid out such as to achieve the best possible fuel consumption
and smooth running of the N14 engine.
Note: The volume control valve must not be replaced individually. Due to the
risk of soiling, the complete high pressure pump assembly must be
replaced as required.
Rail Pressure Sensor
The rail-pressure sensor fitted on the stainless
steel rail. In the rail, the compressed
fuel is stored temporarily and
distributed to the high-pressure fuel injectors.
A silicon element on a metal membrane
measures the fuel delivery pressure in the
rail. The measuring range of the rail-pressure
sensor is from 0 to 160 bar.
The rail-pressure sensor delivers a proportional
voltage over the entire measuring
range.
If the rail-pressure sensor fails, the volume
control valve is activated in emergency
operation by the ECM.
Electrical Fuel Pump
The electric fuel pump is an in-tank pump.
The ECM activates the fuel pump via the
fuel-pump relay. The fuel-pump relay is in
the junction box electronics.
With terminal 15 On, a fuel-pump relay
switches on the electric fuel pump.
High Pressure Fuel Injectors
The high-pressure fuel injector is arranged on the side of the cylinder head and protrudes
into the combustion chamber. This is known as direct injection. In the fully sequential
fuel injection system, the ECM drives each high-pressure fuel injector via its own output
stage. The injection timing of the respective cylinder is adapted to the operating conditions
(engine speed, load and temperature).
The high pressures are required as it is necessary to inject the quantity of fuel necessary
for combustion within a very much shorter space of time.
The graphic on the opposing page shows a sectional view of the high pressure fuel injector.
The coil (5) with current flowing through it produces a magnetic field. As a result, the
injector needle with magnet armature (7) lifts from valve seat (9) against the force of
spring (4) thus releasing the valve outlet holes (10). The fuel is now forced into the combustion
chamber due to the pressure difference between the rail pressure and combustion
chamber pressure.
When the current is switched off, the injector needle is pressed into the valve seat by the
spring pressure thus interrupting the flow of fuel. The valve opens at an extremely fast
rate, it guarantees a constant opening cross section for the time it is open and closes
against the rail pressure.
The injected fuel volume is dependent on the rail pressure, backpressure in the combustion
chamber and the opening time of the fuel injector.
Compared to manifold injection, the fuel is injected faster, more accurately and with better
development of the fuel jet.
A voltage of approximately 100 V is
required to activate the high-pressure fuel
injectors.
The constant current with the high-pressure
fuel injector open is approximately 80
Volts.
The incoming system voltage is stepped
up to 85 V to 100 V by the use of a
clocked output stage with high power
capacitors.
A current flows in the output stage up to a
defined cutout value. As the result of this
cutout, an induction voltage is produced,
e.g. 85 V, that charges the high power
capacitors (booster).
The high pressure fuel injectors are powered
by this capacitor current with a
strength of 2.8 A to 16 A.
The ECM drives the high pressure fuel
injectors on the ground side.

 

You are reading values on the high pressure side of the fuel system, in between the high pressure fuel pump (HPHP) and the fuel rail/injectors. The low pressure pump is probably low-hundreds of PSI, FAR lower than the 1500 or so psi (100+ bar). So the low pressure pump has nothing to do with the pressure slightly increasing when engine turns off.

You mentioned pressure increase slightly and slowly, if it's able to hold that pressure, that would seem to negate the leaky injector theory. You should be able to run the engine, get pressure where you expect it, turn the car off, then turn the car to accessory power. This should keep the obdii on and let you monitor pressure while the car is off. I don't know how long it might take for pressure to drop if an injector is leaking. I do believe there is NOT a pressure relief line, so pressure should hold between HPFP and injectors. NOTE: I could be wrong on this, I'm not certain.

 

Great information and I appreciate the write up. Will definitely help with further troubleshooting.
New development is after letting the vehicle sit overnight, the full rail reading was at 2500 psi, we'll above the 1800 it should never go above. And the engine seemed to hydrolock. By that I mean the starter engaged and something stopped the engine from turning over. Waited a few minutes and it cleared. Very difficult to get started. Fuel Rail psi dropped while cranking to 1200 psi for it to finally start and run great. It stayed in the 1000 to 1750 psi range while idling and reving with the low pressure staying at 98 with no deviation. Even after turning off the car, the low fuel pressure stayed at 98. And the pressure on the rail, when the engine is off, continue to rise at approx 5 psi each update.
Last couple of days has been very rainy so I will pull plugs and check to see if pump in tank turns off with ignition on Friday. I feel I just need to figure out why my pressure is increasing when engine is shut off. Also note that there is no fuel leaking externally or smell of fuel in engine compartment.
I did get errors on each cylinder for Misfire and Misfire with damaging exhaust after start sequence. 2EE2, 2EFE. Cleared them and they did not return. Car is back on the "Princess Pad" until I get this figured out.

 

Looks like this is a secondary issue. This is a heat issue and the heat from the engine when turned off soaks into the fuel rail and raises the pressure. The aux pump does run but it is filling up the bottle, so possibly o thermostat or blockage. Luckily I have a thermostat housing from either fcp or ecs, have to look it up, with a lifetime warranty. But this, the water pump, hoses to the turbo, gasket to oil neck, oil neck cooler and cooler gaskets were all replaced a year ago. I found out by gently running water over rear of engine while pressure was rising and it stopped and started to go back down.
Now I need to figure out if it's a blockage, pump or thermostat.

 

Looks like the heat soaks is coming from the aux pump and fan not coming on after shut off. I can go in Protool and cycle them and stop the pressure from rising on the fuel rail. Now I've gotta find out why they are not coming on after shut off but I can cycle them through software. Any suggestions?

 

That sounds like great troubleshooting there. Perhaps there is a temp sensor or computer control that is faulty. Wish I knew more to help.

 

Update: The aux pump is working and staying on until temp reaches 185. Heat is still soaking into fuel rail and pressure is rising to 2800 in under 10 minutes even after engine is cooling down. Going to replace the hpfp next as I am thinking the control valve isn't releasing pressure after car us turned off. Did monitor pressure while operating and actual pressure matches expected pressure during all ranges of acceleration and idle. Any suggestions on why rail is holding pressure after car is turned off welcome.