BMW Fuel filter heater problem (3-pin or 4-pin)
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
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
Figure 3. Schematic diagram - DDE7, E87, N47 fuel heater.
Fig. 4: Overview, fuel supply with fuel pre-supply pressure control. Low-pressure fuel lines.
Fig. 5. Table. Overview, fuel supply with fuel pre-supply pressure control signals.
Fuel presupply control
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.
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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.