Gasoline Engine Injection System

General Information

Motronic (DME) Injection System Block Diagram
1 — activated charcoal canister
2 — shut-off valve
3 — fuel tank ventilation valve
4 — fuel pressure regulator
5 — injector
6 — pressure transducer
7 — ignition coil
8 — position sensor
9, 10 — positions not used
11 — mass air flow meter
12 — control unit
13 — throttle position sensor
14 — idle speed control valve
15 — intake air temperature sensor
16 — exhaust gas recirculation valve
17 — fuel filter
18 — knock sensor
19 — engine speed sensor
20 — engine coolant temperature sensor
21 — oxygen sensor
22 — diagnostic connector
23 — diagnostic lamp
24 — differential pressure sensor
25 — fuel pump

BMW petrol engines use the Bosch-Motronic management system. It is a combined electronic ignition and fuel injection system, designated Digitale Motor-Elektronik (DME). The ignition and injection systems are controlled by a common control unit. This Section covers the fuel injection system.

The DME system operates reliably over a long period and requires no maintenance. Repairs are extremely rare.

Fault memory

The control unit detects faults in the injection and ignition systems, such as sensor failure, disconnected connectors or leaking contacts. These faults are stored in memory immediately. At the same time, the warning lamp in the instrument cluster illuminates to indicate that a fault has been stored. If a fault occurs only once, for example due to a poor contact, the warning lamp goes out again, but the fault remains stored in memory. In addition, data indicating the frequency of the faults is recorded. A BMW service station reads out and rectifies the faults using a diagnostic tester connected to the diagnostic socket (right side of the engine compartment).

If the engine or fuel injection system malfunctions, it is recommended to read the fault memory data first. The service station can print out a list of faults. For this purpose, an electronic reading device is connected to the vehicle.

All DME versions have an emergency operating mode: if a sensor fails, the control unit continues to operate using the mean value of the monitored parameter of the corresponding sensor. If the air mass meter fails, the control unit uses the throttle position sensor and engine speed signals as the basis for calculating fuel quantity. This control mode is activated automatically and is not indicated in the instrument cluster. Driving continues, and performance is slightly reduced, but this is not noticeable to the driver. The fault is recorded by the control unit. It is therefore recommended to read the fault memory periodically, for example when checking exhaust gas composition, even if no defect is apparent.

* Disconnecting the battery or disconnecting the connector at the control unit erases all faults stored in memory.

Safety precautions and cleanliness rules when working on the fuel injection system

* When working on the fuel system, observe strict cleanliness. Refer to Section Cleanliness rules when working on the fuel system.

• The fuel system is under pressure. Therefore, relieve the pressure in the fuel system before replacing fuel system components. To do this, carefully open the supply line while covering it with a cloth.

• System pressure drops by itself several hours after the engine is stopped.

• Before checking the fuel injection system, make sure the ignition system is serviceable.

• Disconnect and connect the DME control unit connector only with the ignition switched off. Make sure the connection is correct.

• Do not start the engine without the battery securely connected.

• Never disconnect the battery while the engine is running.

• Disconnect the battery before rapid charging. Do not use rapid-charging equipment to start the engine.

• Do not expose the control unit to temperatures above +80 °C.

• When performing a compression test, switch off the power to the DME control unit. To do this, disconnect the main relay. Refer to Section Compression test.