Workshop Hints

Workshop Hints

Before any service work is performed on any fuel system related component, always adhere to the following:
- Observe relevant safety legislation pertaining to your area.
- Ensure adequate ventilation
- Use exhaust extraction system where applicable (alleviate fumes).
- DO NOT OPERATE THE FUEL PUMP unless it is properly installed in the fuel tank and is submersed in the fuel (fuel lubricates the pump).
- DO NOT SMOKE while performing fuel system repairs.
- Always wear adequate protective clothing including eye protection.
- Use caution when working around a HOT engine compartment.
- BMW does not recommend any UNAUTHORIZED MODIFICATIONS to the fuel system. The fuel systems are designed to comply with strict federal safety and emissions regulations. In the concern of product liability, it is unauthorized to sell or perform modifications to customer vehicles, particularly in safety related areas.
- Always consult the REPAIR INSTRUCTIONS on the specific model you are working on before attempting a repair.

Fuel
Fuel quality should always be considered when diagnosing a driveability complaint. The type of fuel, proper AKI rating, impurities and moisture am not factored by the ECM.

Fuel Supply
The fuel supply hardware should be visually inspected for damage that can affect pick-up, transfer, pressure and return.

Please refer to the Repair Instructions on fuel supply hardware.

Fuel Pump and Sending Unit Access







All BMW vehicles have access plates to service the fuel pump and sending unit(s) without removing the fuel tank.

The E46 M3 access plates are located under the rear seat.

The "saddle" type fuel tank (under rear seat) has two access plates.







The passenger side allows access to the fuel pump/sending unit.

The driver side accesses the sending unit/syphon jet.




The M roadster and M coupe have a single access plate located behind the passenger seat.


Draining the Fuel Tank







In order to remove the fuel tank it must be drained first to avoid fuel spills and handling excessive weight. In some cases depending on the fuel tank dimensions (vehicle specific), it is also necessary to drain the fuel tank to replace the sending units and/or fuel pump.






CAUTION: In some vehicles, the sending units/fuel pump is mounted lower than the top of the fuel tank. A fuel spill will be encountered if the fuel is not drained.


NOTE: Consult the BMW Service Workshop Equipment for the proper evacuation equipment. The saddle type tank requires an additional step to drain the fuel from the driver side. The evacuation equipment should be attached to the tank compensating hose (arrow) to drain out the remaining fuel.


Fuel Pump/Pressure Regulator - Testing




The fuel pump should be tested for delivery pressure and volume. Caution when disconnecting fuel hoses because there is the possibility of residual fuel pressure! Install the fuel pressure adapter to the fuel pressure fitting.







Remove the fuel pump relay/module (M roadster/coupe located in the Electronics Box, E46 M3 located in the trunk, above right wheel well - see relay testing in the power supply section). Connect the Relay Bypass Switch to pin 87b and 30 of the relay socket. This will activate the fuel pump without running the engine.




If the 5 bar fuel pressure is not achieved or bleed off is more than 0.5 bar, refer to 13 31 of the Repair instructions for further diagnosis. The Fuel Hose Clamp Tool can be used to isolate bleed off from the pump (non-return check valve) or the pressure regulator (restriction valve). Also verify power supply to the fuel pump.


Fuel volume must be tested to verify:







Fuel Injectors
While inspecting the fuel injectors, consider the following:












Fuel injectors can leak which bleeds off fuel pressure and increases emissions. The injectors can be tested using the Fuel Injector Leakage Tester.

The fuel injectors can be cleaned.

The Fuel Injectors should also be tested for:
1. Resistance
2. Power Supply
3. Status Display - Fuel Injection Signal
4. ECM Final Stage transistor activation. This test function is found under the Oscilloscope Preset list - "Ti Injection Signal". Install the 88 pin adapter, Diagnostic cable MFK 2 positive lead to the ground activation circuit for the injector. This test is performed with the engine running.












Crankshaft Position/RPM Sensor
This sensor should be tested for:
1. Power Supply
2. AC Voltage
3. Status Display
4. Oscilloscope Display Found Under Preset List "Rotation Speed Sensor Signal"







Camshaft Position Sensor (Cylinder ID)
This sensor should be tested using the MoDic for:
1. Power Supply
2. DC Voltage
3. Status Display
4. Oscilloscope Display Found Under Preset List Rotation







Engine Coolant Temperature
This Sensor should be tested using:
1. DISplus/Modic Status Page - Degree C (dependent on engine temperature)
2. DISplus/Modic Multimeter - Resistance