BMW M50TU Technical Information

Reproduced from the BMW TIS.

With the introduction of the 1993 E34 and E36 models, a revised version of the M50 engine is also introduced. The revised four valve, six cylinder engine is designated M50 TU (Technical Update).

The results of the technical revisions are:
· Improved torque curve, particularly in the mid engine speed range
· Lower fuel consumption
· Improved and lower idle speed
· Lower exhaust emissions
· Improved engine response
· Lower engine noise levels

The following design modifications contribute to the improvements made on the new M50 TU engine as compared with the previous M50 engine:
· Introduction of DME M3.3.1 Digital Motor Electronics with knock control.
· Increased compression ratio of 10.5:1.
· Introduction of variable camshaft control (VANOS).
· Reduced valve stem diameters with single valve springs.
· Reduced weight bucket-type tappets and spring plates.
· New pistons and connecting rods.
· Modified crankshaft vibration damper.
· New hot-film mass air flow sensor.
· New idle speed control valve (ZWD-5).

The M50 TU develops 188hp (140kw) at 5900 rpm with maximum torque outputs of 184 lb. ft. (250 Nm) at 4200 rpm (E34) and 181 lb. ft. (245 Nm) at 4200 rpm (E36). Overall internal engine friction and drag torque have been reduced by approximately 15% with the average fuel consumption being reduced by approximately 5%.

Torque/Power Comparison M50 vs. M50 TU

The Bosch Motronic system DME M3.3.1 used on the M50 TU is a further development of the DME M3.3 system used on the M60 engine. See TRI 11 02 92 (2124) for details on the M3.3 system. At this time the CAN (Controller Area Network) bus used on the M60 engine is not used on the DME M3.3.1 system.

The following chart details the most significant improvements over the previous DME M3.1 system used on the M50.

While not presently used in this manner, the software of the Cylinder Individual Fuel Injection (CIFI) system can be programmed for each cylinder on an individual basis, i.e. the duration of injection can differ for the individual cylinders. Presently, the duration of injection is the same for all cylinders.

The knock control system adjusts the ignition timing sufficiently to avoid engine knock and will allow the engine to run satisfactorily (but with reduced power) on fuel of a lower octane rating than the recommended fuel grade. Thus, if the owner accidently gets a tank of lower octane gasoline, the engine will not be damaged.

Variable Camshaft Control (VANOS)

One of the most important design changes introduced on the M50 TU engine is the use of the variable camshaft control system (VANOS). This system improves the engine's mid-range torque output, reduces exhaust emissions, increases throttle response, and improves idle quality by varying the intake valve timing (camshaft position) during operation. VANOS is controlled by the latest Digital Motor Electronics Management System designated DME 3.3.1, depending on engine load, speed and temperature inputs.

Extensive tests were carried out using various intake camshafts and timing intervals to determine the ideal valve spread angles. The spread angles used on the M50 TU are 110° in the retard position and 85° in the advanced position. The intake and exhaust valve lift is 9.0 millimeters.

THEORETICAL VALVE LIFT DIAGRAM - M50 TU/ VANOS

New components incorporated for VANOS include:
· Intake camshaft with helical-cut teeth on the front.
· Timing chain sprocket with internally cut helical teeth.
· Hydro-mechanical camshaft adjusting unit with hydraulic piston and a gear which has helical-cut teeth inside and out. The Hydro-mechanical camshaft adjusting unit is located in a pressure-cast aluminum housing on the cylinder head in front of the intake camshaft.
· Electromagnetic (solenoid) valve.
· Oil pressure connecting line from the rear of the oil filter housing to the electromagnetic (solenoid) valve.
· Actuating and diagnosis electronics in the DME M3.3.1 engine control module.

1 Hydro-Mechanical camshaft adjusting-unit
2 Oil pump
3 Engine control module
4 Oil filter
5 Engine oil pan
6 Electromagnetic (Solenoid) Valve

32,18*28,92

1 Solenoid Valve
2 Control Piston
3 Intake Camshaft
4 Gearwheel with Shaft

Functions of VANOS

The engine control module energizes the solenoid valve which allows engine oil to flow to one of two sides of the piston in the Hydro-mechanical camshaft adjusting unit. The engine oil pressure moves and holds the piston at one of its two mechanical stops. A gear wheel with a shaft rotates inside the hydraulic piston. It converts the piston stroke by way of helical-cut teeth into rotary movement of the camshaft which is relative to the driven sprocket.

The solenoid valve control piston is designed such that when pressure reaches one chamber, the other is at zero pressure (return flow). As soon as the solenoid valve is energized, its armature overcomes the spring force and moves the control piston to the advanced timing position. The coil spring in the solenoid valve ensures that the control piston is returned to the retard position when the valve is de-energized. This also ensures that if the solenoid valve is defective or the actuating system malfunctions, the camshaft is automatically held in or reset to the retarded position since the engine will not start with the camshaft in the advanced setting. The total camshaft travel is 12.5 camshaft degrees (25 crankshaft degrees).

New special tools used to check the VANOS system camshaft adjustment angle are outlined in Service Information Bulletin 04 27 92 (3648).

New lightweight, compact pistons combined with 10.0 mm longer connecting rods reduce oscillating mass and promote smooth running.

The compression ratio is 10.5:1.

For improved noise levels and weight reduction, the M50 TU incorporates a sheet metal (axially decoupled) vibration damper compared to the cast (radially decoupled) M50 damper.

The weight of the hydraulic tappets, upper valve spring retaining plates and valve retainers has been reduced resulting in lower internal friction.

Valve stem diameters have been reduced from 7 mm (M50) to 6 mm (M50 TU) and single valve springs are used to further reduce moving masses.

Technical Data

Design Inline: six-cylinder
Displacement: 2494cc (1 52.2 cu. in.)
Stroke: 75mm (2.953 in.)
Bore: 84mm (3.307 in.)
Max. Power: 188/140 hp/kw
at engine speed: 5900 rpm
Max. torque: E36=245 Nm (181 lb. ft.) E34=250 Nm (184 lb. ft.)
at engine speed: 4200 rpm
Max. permissible engine speed: 6500 rpm ± 40
Compression ratio: 10.5:1
Compression pressure: 10 bar ... 11 bar (minimum) (147 ... 162 psi)
Intake valve diameter: 33mm (1.299 in.)
Exhaust valve diameter: 30.5mm (1.201 in.)
Valve clearance: Self-adjusting, hydraulic
Oil pressure: 4 bar (58.8 psi)
Oil capacity with oil filter: E36-7.0 qts. (6.50 ltr.) E34-6.0 qts. (5.75 ltr.)
Ignition: Direct solid state ignition
Firing order: 1-5-3-6-2-4
Distributor: One ignition coil per cylinder
Spark plugs: Bosch F8LDCR NGK BKR6EK (with dual electrode)
Electrode gap: 0.9mm ± 0.1 mm 0.035 in. (non-adjustable)
CO level: 0.7 ± 0.5% (non-adjustable)
Idle speed: 700 ± 50/min. (non-adjustable)
Fuel injection: DME 3.3.1 with hot-film mass air flow sensor
Recommended fuel: Unleaded gasoline of at least 89 AKI