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bmwBMW Fuel filter heater problem (3-pin or 4-pin)
Due to certain circumstances (fuel system fires), since 2007/2008 BMW has been rebuilding low-pressure fuel lines. There were some problems with the fuel filter heater.
Let's analyse the situation and the problem with BMW fuel filter heater. In the face of some problems that occurred with BMW models manufactured in earlier years, BMW changed some elements of the low-pressure fuel supply system. The design of the fuel heater in the version for diesel engines (DDE electronics) was changed. So far, the system with an autonomous fuel heater was used, which had an integrated fuel temperature sensor and fuel pressure sensor. It is the so-called 4-pin heater, which has four electrical outlets (connectors).
Currently produced BMW fuel heaters have separate heater and sensors (pressure and temperature). This is the so-called 3-pin heater. In addition, these two fuel heater subsystems are not electrically or logistically compatible with each other.
 
fuel-heater
Unfortunately, and due to BMW policy, some original components and spare parts are no longer manufactured. It was possible to buy them until stocks run out. One of these elements is the BMW fuel heater.
 
This element has integrated electronics, temperature and pressure sensors and 4 heating elements and is not serviceable. This is not a good situation for many owners of BMW cars.

 

 

 

 

Figure 1. Fuel heater (4-pin).


Let's analyze the electrical schematics for both cases of the fuel heater: 4-pin and 3-pin heater.


4-pin fuel heater analysis

fuel-heater  

 

 
Fuel heating

The fuel heating unit is integrated in the fuel filter and is activated depending on the temperature and pressure in the fuel filter. Pressure switches and thermostats are also integrated in the fuel filter. The fuel heater only works with the ignition switched on.

The fuel heater is switched on in the case of:

- Fuel pressure > 6 bar and
- Fuel temperature < 2 °C

The fuel heater is switched off again in the case of:

- Fuel pressure < 5.5 bar for a duration of > 5 min OR
- Fuel temperature > 12 °C OR
- During the starting process: if the electronics in the fuel filter detect the battery voltage < 7.5 V for longer than 0.2 s

 

Figure 2. Schematic diagram - DDE6, E91, M47 fuel filter / fuel heater.


3-pin heater

fuel-heater

Figure 3. Schematic diagram - DDE7, E87, N47 fuel heater.  

low-pressure

Fig. 4: Overview, fuel supply with fuel pre-supply pressure control. Low-pressure fuel lines.  

sigs

Fig. 5. Table. Overview, fuel supply with fuel pre-supply pressure control signals.

Fuel presupply control

The fuel supply in the N47 and N57 is ensured by a pressure-controlled system.

Brief component description

The following fuel supply components are described:

DDE control unit with fuel presupply pressure control function

The fuel presupply pressure control function is integrated in the DDE control unit. The DDE determines the current actual pressure in the fuel presupply pressure system via the fuel pressure and temperature sensor. The DDE calculates the control variable from several input variables which is required to adjust the fuel presupply pressure. The fuel pre-supply pressure is adjusted to a pressure greater than 3.5 bar (absolute).

The input variables relevant to determining the control variable are:

  • Actual pressure in the fuel presupply pressure system
  • Engine speed
  • Fuel injection rate

The control variable is sent in the form of a CAN message to the fuel pump control module (EKPS). The control variable is sent in the unit l/h. The value range is 0-254 l/h.

Fuel pressure and temperature sensor

The fuel pressure and temperature sensor is located in the fuel delivery line shortly before the high-pressure pump. The fuel pressure and temperature sensor measures the current is in the fuel presupply pressure system and sends the signal to the DDE control unit. The fuel temperature is also measured by the fuel pressure and temperature sensor for further functions in the DDE.

Fuel pump control module

The fuel pump control module receives the control variable of the control loop from the DDE as a CAN message. The CAN message value is converted into a voltage in the fuel pump control module using a characteristic curve. This voltage is used by the fuel pump control module to activate the electric fuel pump.

Electric fuel pump

The electric fuel pump is activated by the fuel pump control module with a voltage of 6.5 - 15 V.

For correct monitoring of the power consumption of the electric fuel pump, an adaptation value is stored in the DDE. The electric power consumption of the electric fuel pump at minimum actuation is stored with this adaptation value. The lower limit value for monitoring the power consumption of the electric fuel pump is calculated with this adaptation value.

Fuel filter heating

The electric fuel filter heating is integrated in the fuel filter and activated by the DDE control unit.

The fuel filter heating is switched on when:

  • Fuel temperature less than 0 °C AND
  • Current power consumption of the electric fuel pump is less than the sum of the adaptation value of the electric fuel pump and the adjustment value. The adjustment value is determined from a characteristic map and dependent on engine speed and fuel injection rate.

Notes for Service department

Diagnostics instructions

Control of the fuel presupply pressure is monitored by the DDE. Faults which arise as a result of control deviations are stored in the DDE fault memory.

Actuation of the electric fuel pump is monitored by the fuel pump control module. Faults that occur are stored in the fault memory of the fuel pump control module.

When the DDE control unit is woken by a signal (wake-up), the electric fuel pump control unit is still not awake; the electric fuel pump is briefly activated for approx. 10 ms.

The electric fuel pump is not activated when terminal 15 is switched on. The electric fuel pump is activated only when the starter motor is actuated.

Note! Observe the corresponding service function when replacing certain fuel system components.

Final autor's note.

The two BMW M47 and N47 fuel heater systems are significantly different in design.
The M47 fuel heater is an autonomous system, while the N47 fuel heater is not. Fuel heater N47 control comes with signal line S_KSH from DDE7.
BMW 3-pin and 4-pin fuel heaters are not compatible. Only the connector on the fuel heater is mechanically compatible. Unfortunately such "compatibility" is not enough.

So do not buy a 3-pin fuel heater for your BMW with a 4-pin fuel heater and vice versa.
 
ZYGI-BMW