PROJEKT36 · WIRING

M50 engine management

The M50 non-VANOS engine wiring around the Bosch M3.1 DME, in four parts: power and relays, injection and ignition, sensors, and the dashboard and diagnosis links. Hover or tap a wire to follow it; tap a part for what it does.

M50B25 non-VANOS with DME M3.1, from the Bentley 1992 2.5L diagrams (US market). Colours converted to BMW's German codes; this source gives no wire sizes. On a phone, scroll the diagram sideways.

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SW blackRT redGN greenBL blueGE yellowBR brownWS white GN/SW = green with black stripe supply / ground of a part shown elsewhere

Power supply and relays

RT terminal 30 RT/WS injectors 1–6 RT/WS idle · purge · MAF BR BR/GN BR/GN GN/VI X10016 · 15 X10016 · 16 G312 GN/BL O2 heater BR G103 Front power box Main relay (DME relay) coil 86–85, grounded by DME pin 27 87 30 86 87A 85 Front power box Fuel pump relay coil 86–85, grounded by DME pin 1 30 86 85 87 Front power box Oxygen sensor relay feeds the O2 sensor heater 30 86 85 87 DME Engine control module, Bosch M3.1 88-pin connector 26 54 27 1 37 6 34 55 F18 Fuse 15A M Fuel pump in the tank 2 1

How it works

DME pin 26 and the main relay (terminals 30 and 86) have battery voltage at all times.

With the ignition on, the DME grounds pin 27 and the main relay pulls in. Terminal 87 then feeds the injectors, and 87A feeds DME pin 54, both relay coils, the idle valve, the purge valve and the air-flow meter.

The DME switches the fuel pump relay through pin 1. Bentley's pin table notes that it needs the crankshaft signal, so the pump only runs while the DME sees the engine turning.

Pin 37 switches the oxygen sensor relay, which powers the sensor heater.

Check on your car

  • The Bentley wiring page prints the fuel pump fuse F18 as 5A. The fuse chart (and the fuse & relay guide) give 15A, which is what this diagram shows.

Redrawn from Bentley ELE-72 and ELE-73, Engine Management 1992 2.5L (M50, DME M3.1, US market); diesel and M3 parts are left out.

Injection and ignition

RT/WS main relay 87 BR/WS BR/RT BR/GE BR/BL BR/GN BR/VI GN BR G119 Cyl 1 Injector 1 2 Cyl 2 Injector 1 2 Cyl 3 Injector 1 2 Cyl 4 Injector 1 2 Cyl 5 Injector 1 2 Cyl 6 Injector 1 2 DME Engine control module, Bosch M3.1 3 5 4 33 31 32 25 23 24 50 52 51 56 Cyl 1 Coil 1 3 2 Cyl 2 Coil 1 3 2 Cyl 3 Coil 1 3 2 Cyl 4 Coil 1 3 2 Cyl 5 Coil 1 3 2 Cyl 6 Coil 1 3 2 S2 Ignition switch terminal 15: run and start 15

How it works

All six injectors share one red/white supply from the main relay. The DME opens each one by grounding its own wire (pins 3, 5, 4, 33, 31, 32), so injector timing and length are set entirely by the DME.

Each cylinder has its own coil. Terminal 15 from the ignition switch feeds pin 3 of every coil and DME pin 56; the DME fires a coil by switching its pin 1 (pins 25, 23, 24, 50, 52, 51).

The coils share a ground at G119.

Redrawn from Bentley ELE-72 and ELE-73, Engine Management 1992 2.5L (M50, DME M3.1, US market); diesel and M3 parts are left out.

Sensors and actuators

GE SW GE SW SW GE GR RT/GE BR/SW BR/RT GR/BL GR/WS GR/GE WS/GE WS/GN BR GN/BL O2 sensor relay 87 G103 G103 BR RT/WS main relay 87A G103 (also data link pin 19) BR/OR G103 Sensor Crankshaft position / rpm inductive, shielded 1 2 3 Sensor Camshaft position cylinder identification 1 2 3 Sensor Heated oxygen sensor 4-wire: signal + heater 1 2 4 3 Sensor Intake air temperature 1 2 Sensor Throttle position 3 = 5 V supply · 2 = signal 3 2 1 Sensor Engine coolant temperature 1 2 Sensor Mass air flow sensor hot-wirepin 3 not used 6 5 1 2 4 Valve Idle speed control valve two-coil rotary valve 1 3 2 Valve Evaporative purge valve 2 1 DME Bosch M3.1 engine control module 67 68 44 16 71 70 77 59 12 78 43 41 14 13 2 29 36 28

How it works

The crankshaft and camshaft sensors are inductive: each makes an AC signal on a pair of wires inside a shielded cable. The DME uses the crankshaft signal for rpm and timing and the camshaft signal to tell which cylinder is on its firing stroke.

The temperature sensors and the throttle sensor share one ground, DME pin 43. The DME feeds the throttle sensor 5 V on pin 59 and reads its position on pin 12.

The hot-wire air-flow meter is fed from the main relay. After shutdown the DME pulses pin 13 to burn the wire clean.

The idle valve has two coils; the DME pulses pins 2 and 29 to close or open it. Pin 36 switches the evaporative purge valve.

Check on your car

  • Oxygen sensor pins 70 and 71 on the M3.1: this Bentley wiring diagram puts the black signal wire on pin 71 and the sensor ground on pin 70, and some sources say early M3.1 cars vary. Bentley's M3.1 pin tables list them the other way round (70 signal, 71 ground). With the engine warm, the signal pin swings between about 0.1 and 0.9 V against ground; the ground pin stays near 0 V.
  • This applies to the M3.1 only. On the M3.3.1 (M50 VANOS, 1993–1995) Bentley puts the oxygen sensor on pins 13 and 40; pins 70 and 71 are the knock sensor and its ground there.

Redrawn from Bentley ELE-72 and ELE-73, Engine Management 1992 2.5L (M50, DME M3.1, US market); diesel and M3 parts are left out.

Dashboard, diagnosis and A/C

fuse F27 5A · X10017 pin 14 GR SW/WS SW WS/SW SW/VI WS/VI WS/GE GN/BL RT terminal 30 G103 SW/BL VI/GR SW/GR BR/GR BR/OR fuse F28 5A · X10017 pin 16 terminal 30 main relay 87A Cluster Instrument cluster Check Engine lampspeed out · rpm and fuel in 23 X16·16 X17·2 tach fuel OBC On-board computer D100 Data link connector 20-pin, under the bonnet 1 20 15 18 14 19 A/C Climate control comp req A/C Pressure switch 2 Relay Normal speed relay 5 DME Bosch M3.1 engine control module 8 73 74 17 81 88 87 60 48 86 85 64 11 65 EGS Transmission control module automatic gearbox only 28 37 9 21 11 13 25 4 55 26 X511 Range switch park / neutral contact 7 5

How it works

The Check Engine lamp is fed from fuse F27 and lit when the DME grounds pin 8.

The cluster sends road speed to the DME (pin 73); the DME sends engine speed (pin 74) to the rev counter and the data link connector, and fuel consumption (pin 17) to the cluster.

Diagnosis runs over pins 87 and 88 to the 20-pin data link connector under the bonnet (pins 15 and 20). Pin 18 carries the programming voltage.

The climate control asks for the compressor on pin 86; the DME switches it through pin 48 and watches the A/C pressure switch on pin 85.

With an automatic gearbox, the EGS shares engine speed, throttle, fuel consumption and the diagnosis lines, can retard the timing during shifts (pin 64), and the range switch tells both units when the car is in park or neutral.

Redrawn from Bentley ELE-72 and ELE-73, Engine Management 1992 2.5L (M50, DME M3.1, US market); diesel and M3 parts are left out.

Reading the wire codes

BMW labels every wire with its size and colour, for example 2.5 SW/GE: 2.5 mm², black (schwarz) with a yellow (gelb) stripe. Connectors are numbered X…, followed by the pin. The source for these diagrams gives colours but not wire sizes, so every wire is drawn at the same thickness.

Codes used here: SW = black, RT = red, GN = green, BL = blue, GE = yellow, BR = brown, WS = white.