N43/N53 fuel supply

 

Many have heard about HPFP (high-pressure fuel pump) recalls in the beginnings of N43/N53, also for vehicles, which are in use now, error messages regarding fuel pressure are very often. Unfortunately due to faulty diagnostics, very often HPFP is mistakingly identified as faulty fuel supply element.

In this entry – everything, you have to know regarding fuel supply. Refers to all BMW engines with direct injection, specific parameters – to N43/N53.

 

N43/N53 has two fuel pumps:

LPFP (low-pressure fuel pump) – placed un fuel tank, on the passenger’s side;
HPFP (high-pressure fuel pump) – placed in the motor room, with chain drive from the engine.

 

LPFP performs following functions:

  • supplies HPFP with fuel (pressure: 5000 hPa);
  • pumps the fuel from driver’s side container to passenger’s (pump) side container.

 

HPFP performs following functions:

  • provides stabilized high-pressure rail pressure 150 .. 200.000 hPa in standard mode;
  • 5000 and 100.000 hPa stabilized fuel pressure in emergency modes.

 

LPFP has a DC motor, which is supplied by the 12V onboard network with help of PWM. The management of pump is performed by pump management unit, which is located in the rear of the car, in the trunk. As already mentioned before, LPFP provides stabilized 5000 hPa pressure, which is controlled by fuel low-speed rail sensor, which is located not far from HPFP.

HPFP is directed by a solenoid, which is directed with PWM (by DME) and is located in the pump.

The pressure of HPFP is controlled by high-pressure fuel rail sensor, which is located at the end of the highway, after the last cylinder.

 

Low-pressure sensor marked with a red circle:

 

High-pressure sensor marked with red circle:

 

Low-pressure pump.

In the image: fuel tank construction of BMW

How the fuel pump pumps fuel to “right” side?

Part of flow, created by the fuel pump, is directed via fuel pipe(11), where it “catches” with it fuel, which is on the container on passenger’s side and directs it to pump’s (2) container (3).

How to check, if the fuel pumping is working?

Using INPA, from main menu:

choose Body;
choose Instrument cluster;
press F5 (Read Status);
choose F1 (Read Status Analog 1).

Lever-type sensor 1: fuel level sensor, pump’s side

Lever-type sensor 2: fuel level sensor, driver’s side

If the total amount of fuel is less than half of the tank (37 liters/E60), ALL fuel has to be pumped to the side of the pump (fuel level sensor of other side has to show 0 liters). If total fuel amount is higher, the largest part of it (37liters/E60) has to be on pump’s side (largest indication – sensor No.1).

Of course, when the driving is very dynamic, fuel can partly leak other (“incorrect”) side. In this case, the driver’s side sensor can have increased indication, but in such situation, the fuel pump immediately has to start to pump fuel to “correct” site. Pumping speed has to be around 1 liter in 5 to 7 seconds. It means, that the indications of the 1-st sensor have to grow, and the indications of other side have to decrease, till:

  • the container in pump’s side is full (37 liters/E60) OR
  • sensor No.2 indicates 0 liters: no more fuel to pump.

 

How to check fuel pumping after repair of the system (replacement of pump, fuel strainer, change of filter etc.)?

The recommended total fuel amount in the tank: to/around 20 .. 25 liters. Pour over 5 .. 10 liters from pump side container to driver’s side container. Switch on the engine, monitor fuel level indications. The indication of the first sensor has to decrease with speed 1 liter in 5 to 7 seconds, the indication of the second sensor – has to decrease for one liter, till it reaches 0.

How to evaluate fuel pressures?

Open with INPA../F5/F2/F6

Pressure of low-pressure pump: right side, bar No.5;

The pressure of high-pressure pump: right side, bar No.6.

 

Correctly working fuel supply of running engine (video):

 

In the beginning of the video: idle.

As can be seen,

  • 5000 hPa is maintained (an indication of the sensor) in area 4970 .. 5030 hPa, it means,: +/- 0,6%;
  • 200.000 hPa is maintained (indication of sensor) in area 198.000 .. 202.000 hPa, t.i.: +/- 1%

In the 24-th/34-the second of the video, the accelerator pedal is sharply pressed in “kick down” mode and released, as soon as the engine reaches 6000 RPM.

As we can see, the low-pressure pump maintains stable 5000 hPa in the moment of swift increase of fuel consumption, around 20% (or 1000 hPa) over-shoot after a swift decrease of fuel consumption and slowly drops down to 5000 hPa (reaction to rapidly changing fuel demand is pretty good – aperiodic).

The high-pressure pump maintains stable 200.000 hPa in the moment of swift increase of fuel consumption and around 38.000 (or around 19%) over-shoot after a swift decrease of fuel consumption, then fuel pressure drops down to 185.000 hPa for a second (the so-called impulse response: reaction to rapidly changing incoming fuel pressure and fuel demand is far away from ideal – ‘swell’ is observed).

 

PWM of low-pressure pump is seen here: ../F6/F1/F5

Correct values in idle: 50 .. 60%; driving smoothly (50 .. 100 km/h), PWM increases for around 5 .. 10%.

 

In this video you can see the correct performance of the pump (valve):

 

On 10/th/24-the second the swift pressing of the accelerator pedal (as described above) is done (“kick down” mode), the rest of the time – idle. As we can see, in the moment of swift fuel consumption increase PWM, directed to pump, reaches 75%, after that for 3 seconds (while the pressure goes down from 6000 to 5000 hPa) is maintained in 53% (obviously, to avoid swift changes in fuel flow speed – fixed PWM value is maintained, according to pump management map; PWM value – slightly lower than in current situation needed to maintain the pressure).

 

Test block of high-pressure pump: INPA ../F6/F2/F6

Note: manual management of fuel pump is possible only in Homogeneous mode. If the engine runs in Stratified charge, turn on the Homogeneous mode before starting the test.

How to diagnose the fuel supply?

  1. Evaluate pressures, maintained by LPFP and HPFP, and their stability (in idle, HPFP maintains 150 .. 200.000 hPa; in engine working mode: 200.000 hPa). Moreover, if the pressure of LPFP is unstable (jitter is above +/-1%), it’s only self-explanatory, that the pressure of HPFP will be unstable;
  2. Evaluate ability of LPFP to maintain the pressure: LPFP pressure after switching off the engine can go down to 4500 hPa (not lower) during 15 seconds;
  3. Evaluate speed of HPFP drop-down after switching off the engine. Drop-down from 200.000 hPa to 5000 hPa, in 3 .. 4 seconds, not faster;
  4. Check ability of LPFP to maintain necessary pressure in case of rapidly increasing and large fuel consumptions. Evaluate LPFP PWM:
  • idle, swiftly pressing accelerator pedal in “kick down” mode;
  • rapidly increasing in gear 2 & 3.

PWM can be increased upto 75 .. 80%. The increase of PWM till 99% means, that even with maximum electrical power supply (around 2 .. 3 times above norm) the pump is not able to maintain pressure 5000 hPa: there are serious problems in the low-pressure system.

Double-check low and high fuel pressure using manometer!

 

Most common specific error messages (error messages, which do not directly identify faulty component):

 

29F1 fuel pressure, plausibility (HPFP pressure)

2AAF fuel pumpe, plausibility (LPFP pressure)

 

The error messages regarding plausibility are registered, if:

  • the pressure of pump fluctuates at a specific power (LPFP – electrically inquired by PWM or HPFP – PWM of the exact solenoid) – is unstable, or “from another side”;
  • to maintain stable pressure (according to indications of sensors), the necessary power of pump (PWM) significantly fluctuates and does not correspond to pump “profile” (PWM/power map).

 

As can be seen from videos above, the HPFP pressure, obviously, significantly depends on the pressure applied from LPFP, accordingly – the ability of LPFP to maintain the quality pressure of 5000 hPa has to be evaluated at first!

Situations, when the error messages regarding plausibility and even inability to maintain the pressure are recorded for HPFP, but it (HPFP) actually has low-quality power supply, are also possible – the problems with low-pressure system has to be solved at first (for now, the LPFP pressure still manages to comply with requirements – for this reason, no error messages has appeared regarding real problem cause, see note below).

There are also situations, when, mistakingly interpreting error messages, instead of LPFP (or even only fuel strainer, filter, an element of pumping system) much more expensive HPFP is being replaced. Only if the LPFP maintains stable pressure (both pressure and PWM of the valve in modes mentioned before), there is a reason to check HPFP.

Even if error messages regarding HPFP plausibility and/or unavailability to maintain the pressure and the LPFP maintain stable 5000 hPa pressure, the repairs of HPFP has to be started with checking its valve and pressure sensor (and their connection).

Note: each self-regulating system (closed loop system: fuel pump controlled by PWM using pressure sensor in this situation) has a limited time response (time lap between measured and compensated values of required parameter, in this situation – fuel pressure), specific short-time response (overshoot, as we saw in the video, for example). HPFP reaction to rapid fluctuations of initial (delivered from LPFP) fuel pressure is unpredictable. For example, if jittering of low-pressure fuel pump rises from 0,6% to 1,8% (3 times), fluctuations of high-pressure may become 5 .. 10 .. 15 times higher!

One of the most popular reasons for registering error messages mentioned before – the air is being sucked into the system. The cause – LPFP doesn’t pump fuel (in sufficient quantity) to “it’s” side (causes – damaged pump, clogged strainer for reverse fuel pipe; non-hermetic reverse fuel type in the fuel tank).

 

Attention! If there are stored errors relating fuel supply (also check Info and History memory), MSD stops the creation of all kind fuel adaptations!
Normal operation of the engine is NOT restored if/when the status of error messages is/become passive. Moreover, normal operation is NOT stored after erasing of error messages.

How to restore normal operation (re-enable creation of fuel adaptations) after all problems with fuel supply are fixed?
All error messages should have passive status (nicht vorhanden) and not appear after they are cleared;
1. Clear all error messages;
2. Clear 2nd group of adaptations: ../F8/F2/Shift + F9*;
3. Perform new initial adaptations as described here.

*if your vehicle is equipped with OEM NOx sensor, proceed desulphation session BEFORE clearing adaptations! Description here.

 

 

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