With the introduction of the M42 powered E36 models, the successful and proven M42 four cylinder engine has been revised.
The new M42 Engine includes a two-section "Differential Air Intake System" (D.I.S.A.) and an adaptive-selective knock control system as well as other design changes.
With these changes the revised M42 engine develops 137 hp (103 kW) at 6000 rpm and a maximum torque of 175 Nm (129 lb-ft) at 4600 rpm. The increased torque in the medium speed range (5% increase) makes the engine considerably more flexible as compared to the E30 (M42) version.
The differential air intake system (DISA) offers the advantages of both short and long intake pipes, which contributes to improved power, torque and fuel efficiency.
The intake manifold is produced using a new low pressure chill casting process. This process permits thinner walls, reducing the weight of the intake system assembly. The system consists of four ram air pipes, branch pipes (with connecting flap valve), primary intake pipes and a plenum chamber.
1 Primary Intake Pipes
2 Plenum Chamber
3 Ram Air Pipes
4 Branch Pipes (with connecting flap valve)
Short air intake pipes increase power output at the upper end of the engine's speed range, but torque is then relatively low in the medium RPM range. Long air intake pipes boost torque in the medium speed range. The primary air intake pipes lead to cylinder group 1 and 4 and to group 2 and 3, respectively, on the new DISA equipped M42 engines.
With the connecting flap valve closed, the primary pipe and the ram air pipe act together as a single, long air intake pipe. The column of air oscillating in this combined pipe significantly increases engine torque in the medium engine speed range.
1 Ram air pipe
2 Changeover flap pipe
3 Primary intake pipe
In order to obtain more power at higher engine speeds (above approx. 4800/min), the connecting flap valve between the intake air pipe assemblies for the two cylinder groups is opened. This largely eliminates the dynamic effect of the air in the primary intake pipes. The shorter ram air pipes now take over and yield greater power at the upper end of the engine-speed range.
The DISA connecting flap valve is actuated electro-pneumatically in response to a signal from the engine control module. The flap valve begins to open as engine speeds rise above 4840/min, and closes when the speed drops below 4760/min.
The action of the valve is deliberately delayed (hysteresis) to prevent it from opening and closing repeatedly within a short time.
The flap valve control system incorporates:
· a vacuum can with pneumatic actuator
· a vacuum reservoir
· a solenoid (electromagnetic) valve
· a non-return (check) valve
· various connecting hoses
1 Solenoid valve
2 Connecting flange, upper/lower sections
3 DISA flap valve
4 Vacuum can and pneumatic actuator
5 Vacuum reservoir
6 Non-return valve
In the part-load engine operating mode, the vacuum reservoir is evacuated by intake manifold vacuum. The connecting flap valve is kept closed by the vacuum can and pneumatic actuator.
If the engine speed of 4840/min is exceeded, the engine control module de-energizes (switches off) the solenoid valve. This vents the vacuum can, so that the flap valve can open.
As soon as the solenoid valve switches over again (when engine speed drops to 4760/min), the vacuum reservoir and the vacuum can are connected together again and the flap valve closes.
This form of control ensures that the connecting flap always remains open if there is any malfunction of the electro-pneumatic actuating mechanism, and therefore that full power output is guaranteed in the upper engine-speed range.
In other words, the flap valve's basic setting is "open".
The flap is held open or returned to the open position by two springs:
· 1 spiral spring on the flap shaft
· 1 helical spring in the vacuum (diaphragm) chamber
The solenoid valve is actuated directly by a high-power output stage in the engine control module. This output stage can accept a maximum electrical load of approx. 1 Amp.
The new knock control system is incorporated for the first time on a U.S. BMW model which also contributes to the improved performance of the E36 M42 engine.
If an engine runs for any length of time with knock occurring, it may suffer severe damage.
Knock is encouraged by:
· a high compression ratio
· a high level of cylinder filling
· poor-quality fuel (low octane number)
· high intake-air and engine temperatures.
An artificial increase in the compression ratio may also be caused by carbon deposits in the combustion chambers, or as a result of an unfavorable combination of manufacturing tolerances.
If the engine has no form of knock control, the ignition timing has to include a safety margin to allow for such unfavorable influences, so that efficiency is automatically lowered in the full-load operating range.
Knock control enables the engine to run right up to the knock limit, since it retards the ignition (on the affected cylinder only) when the actual risk of knock is detected. The normal ignition timing can therefore be chosen for optimum fuel consumption and operating efficiency, without allowing any safety margin for influences which could cause the knock limit to be exceeded.
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 unleaded premium. Thus, if the owner accidentally gets a tank of inferior gasoline, the engine will not be damaged immediately.
Advantages of knock control:
· avoid damage caused by knock even in the most unfavorable circumstances
· maximum economy, since the energy in the available grade of fuel is fully utilized and the engine's operating condition is taken into account
· fuel consumption is reduced and torque maximized throughout the upper engine-load range, particularly when the DISA system increases the mixture charge entering the cylinders.
To ensure that knock is reliably identified, BMW installed two knock sensors on its four-cylinder engines (many otherwise comparable systems for four-cylinder engines use only one sensor).
A multiplexer circuit in the engine control module analyzes the signals. This ensures that only the signal from the cylinder in which combusion is actually taking place is transmitted to the adjacent knock sensor. The multiplexer is switched correctly by evaluating the signal from the cylinder identification sensor (on the camshaft). The knock sensor is a piezoelectric conductor-sound microphone with a broadband characteristic. A piezo-ceramic ring is clamped by a spring washer between a seismic mass and the sensor body. If the seismic mass is accelerated, it exerts a force on the piezo-ceramic element. Opposed electrical charges build up on the upper and lower ceramic surfaces, and generate a voltage at the contacts. In this way, acoustic vibrations can be converted into electrical signals. These in turn are transmitted by shielded wires to the engine control module for processing.
1 Shielded wire
2 Cup spring
3 Seismic mass
5 Inner sleeve
6 Piezo-ceramic element
The knock sensors are bolted to cast bases on the intake side of the engine block, between the 1st and 2nd and between the 3rd and 4th cylinders.
These locations ensure that even when knock is only slight that the acoustic vibrations emitted from the combustion chambers are transmitted reliably to the knock sensors.
If the actual value exceeds a predetermined value, the combustion process in that cylinder is identified as "knock". The ignition timing is then retarded immediately in that cylinder so that knock is eliminated.
After this, the ignition is advanced again step by step until the optimum value as stored in the mapped ignition program is reached, or until knock is once again detected.
The ignition is retarded even if knock is only slight and does not yet represent any acute hazard for the engine.
Knock control is out of action at engine temperatures below 35° C (95°F) and at low loads (below approx. 1/3 volume air flow sensor load signal).
If noise from the engine is unusually loud, reliable knock identification cannot be guaranteed (for instance above-average valve closing noise caused by a defective hydraulic valve lifter (HVA) or one which is malfunctioning due to lack of oil).
The knock control system's self-diagnosis function consists of the following tests:
· sensor signal malfunction, open circuit (broken wire), defective plug etc.
· self-test of complete analysis circuit
· checking the basic engine noise level as registered by the knock sensors.
If a fault is detected in one of these tests, the knock control is shut down. An emergency program takes over ignition timing control, and the fault is stored in the fault memory.
The emergency operating program ensures that the engine can run without risk on fuel with a minimum octane number (Research Method) of 91. It takes load, engine speed and engine temperature into account.
The diagnosis routine is unable to detect whether the plugs for the two sensors or the sensors themselves have been accidentally interchanged.
During service work, assure that the sensors are connected correctly (see Repair Manual).
The knock control and differential air intake control functions have been added to the Engine Control (DME M1.7) system.
The engine control module has been revised in design so that it still needs only one circuit board despite the additional functions.
The engine control module initiates and monitors the following functions:
· knock control (2 sensors)
· DISA control
· ignition timing
· semi-sequential fuel injection
· adaptive oxygen sensor control
· adaptive idle speed regulation
· adaptive fuel tank venting
· mixture enrichment during warming-up
· mixture enrichment when accelerating
· dynamic overrun fuel cutoff
· catalytic converter protection
· emergency operating program
· version coding
Block diagram of DME M1.7 for M42/E36
The M42/E36 engine is equipped with an integrated primary/secondary crankcase vent system, in order to keep the level of moisture condensate in the intake air passing through the throttle body as low as possible. This avoids contamination of the idle speed control valve and the throttle body.
The primary crankcase vent operates through a large-bore flexible hose which discharges into the air intake system ahead of the throttle body plate (butterfly).
The secondary crankcase vent discharges into the air intake system by way of a channel integrated into the throttle stub pipe housing. In this channel there is a 1.8 mm diameter nozzle to control the flow volume.
1 Air flow
2 Secondary crankcase vent
4 Primary crankcase vent
5 To valve cover
Two heating elements on the throttle body, through which the coolant flows, ensure that the crankcase vent system is intensively heated.
The secondary crankcase vent continues to function until well into the part-load operating range. The primary crankcase vent only takes over when the full-load operating range is reached, the changeover being governed by the difference in pressure between the crankcase and the air intake system.
A new dual electrode spark plug is used in the E36 M42 engine which features 2 nonadjustable electrodes and a 14mm thread. The new spark plug, Bosch designation F7LDCR (or NGK BKR 7EK), is designed specifically for the M42 powered E36 models and is not interchangeable with the E30-M42 Tri-Electrode spark plugs.
Three Way Catalytic Converter
A redesigned catalytic converter distributes the exhaust gas uniformly as it enters the converter through a lateral discharge outlet, so that it strikes the entire surface of the monolith. This improves durability and ensures that emissions from the exhaust system are reduced to a consistently low level.
1 Exhaust gas flow
2 Exhaust gas flow
X immediate inlet surface area
Noise radiating from the converter casing has been reduced by using a rigidly constructed inlet cone of smaller diameter.
Engine designation: M42 B18
Engine code: 18 4 S1
Design: 4 cylinder inline (DOHC)
Displacement: 1796 cc (1 09.6 cu. in.)
Stroke: 81 mm (3.189 in.)
Bore: 84 mm (3.307 in.)
Power: 103 Kw (137 HP)
At engine speed: 6000 RPM
Maximum torque: 175 Nm (129 lb-ft)
At engine speed: 4600 RPM
Maximum permitted engine speed: 6500 + 40 RPM
Compression ratio: 10:1
Intake valve diameter: 33 mm (1.299 in.)
Exhaust valve diameter: 30.5 mm (1.201 in.)
Oil pressure at idle/max speed: 1.3-2.0 bar (18-28psi)/4.0-4.3 bar (57-61 psi)
Oil capacity with oil filter: 5.0 ltr. (5.25 qts.)
Coolant thermostat: 88°C (190°F)
Engine Control: Digital motor electronics (DME) M1.7
Firing order: 1-3-4-2
Spark plug (dual electrode): 0.9 mm 0.035 in., non adjustable electrode gap
CO value at idle: 0.7 + 0.5%, non adjustable
Idle speed: 850 + 40 RPM
Recommended Fuel: Premium unleaded gasoline 90 AKI (95 RON)