Volkswagen 4.2l V8 4V FSI Engine: Design and Function

Introduction

The 4.2l V8 4V FSI engine is a further example of direct petrol injection. It replaces the 4.2l V8 5V engine in the Touareg. Apart from the common cylinder bank angle of 90°, the two engines are no longer comparable.

With an output of 257 kW and 440 Nm of torque, the engine offers very good performance, outstanding dynamics, and a high level of ride comfort. This engine has already been launched in the Audi Q7.

Diagram shows a detailed view of the 4.2l V8 4V FSI engine.

This self-study programme provides information on the design and function of this new engine generation.

✨ NEW

? Important Note The self-study programme shows the design and function of new developments. The contents will not be updated. For current testing, adjustment and repair instructions, refer to the relevant service literature.

Engine Mechanics

Chain Drive

In the 4.2l V8 4V FSI engine, the camshafts and ancillary units are driven via a total of four roller chains on two levels. The chain drive is maintenance-free and reduces engine length. The crankshaft drives two drive gears for the camshaft timing chains via chain drive A. These drive gears, in turn, drive the camshaft adjusters for the exhaust and inlet camshafts via chain drives B and C. Chain drive D connects the crankshaft to the drive chain sprocket for ancillary drives, which powers the spur gear for the ancillary units. The chains are tensioned by hydraulic spring tensioners.

Diagram illustrating the chain drive system, showing the crankshaft, drive gears, camshaft adjusters, chain drives A, B, C, D, spur gear, and guide chain sprockets.

The chain drive is maintenance-free and designed for the engine's service life. For repairs, consult ELSA.

Ancillary Unit Drive

Ancillary units are driven by the crankshaft via chain drive D, a spur gear drive, a gear module, and four intermediate shafts. The oil pump, coolant pump, power steering pump, and air conditioner compressor are driven. The gear module adapts the rotational speed and delivery rate of the coolant and oil pumps.

Diagram showing the ancillary units driven by the crankshaft, including the air conditioner compressor, coolant pump, gear module, power steering pump, oil pump, and spur gear drive.

Intake System

Similar to the 4.2l V8 5V engine in the Touareg, the fresh air intake system features two branches to reduce pressure losses. Both intake tracts converge before a common throttle valve module. Each tract is equipped with a hot film air mass meter for accurate intake air mass measurement.

Diagram of the intake system showing two intake tracts, throttle valve module, and hot film air mass meters for cylinder banks 1 and 2.

Variable Intake Manifold

The two-stage variable intake manifold is made of die-cast magnesium. It incorporates change-over flaps for the variable intake manifold and intake manifold flaps for flap change-over.

Close-up diagram of the variable intake manifold showing change-over flaps and intake manifold flaps.

Switching between short and long intake manifold configurations occurs based on a performance map. In lower engine speed ranges, it uses the torque position (long manifold); in upper ranges, it uses the output position (short manifold). The variable intake manifold motor actuates the change-over flaps via selector shafts and a linkage system. Sealing lips on the flaps ensure leak-tightness in the torque position.

Diagram showing the variable intake manifold motor and selector shaft with change-over flaps.

Intake Manifold Flap Change-Over

Intake manifold flaps are located in the lower intake manifold sections and are actuated by an intake manifold flap motor and linkage systems based on load and engine speed. At low load/speed, they close off lower intake port sections, creating cylinder-shaped airflow. At high load/speed, they are inactive to avoid flow losses. Their positions are monitored by two intake manifold flap potentiometers for emission control.

Diagram illustrating intake manifold flaps, separating plate, intake manifold flap motor, and intake manifold flap potentiometers.

Cylinder Block

The cylinder block is constructed from an aluminium-silicon alloy using low-pressure gravity die casting, offering high strength, low cylinder warming, and good thermal dissipation. Cylinder liners are omitted for a narrower web design. Final cylinder bore machining involves a three-stage honing and exposure process, which exposes silicon particles for wear resistance against pistons and rings. The ladder frame, also from aluminium-silicon alloy, features cast-iron bearing caps for strength and thermal expansion management, limiting main bearing clearance and providing high stiffness.

Diagram of the cylinder block, ladder frame, and cast-in bearing caps.

Crankshaft Drive

The crankshaft is made of high-quality tempered steel and supported at five points. Connecting rods are manufactured using the cracking method. Pistons are forged for strength, with piston crowns optimized for FSI combustion and piston skirts coated with Ferrostan to prevent wear.

Diagram showing the crankshaft, cracked connecting rod, piston crown, and piston skirt.

Cylinder Heads

The 4-valve cylinder head is made of aluminium alloy for good thermal conductivity and strength. Intake manifold flap change-over plates are in the intake ports. Injectors are fitted on the intake side. High-pressure fuel pumps are driven by dual cams on the inlet camshafts. The plastic cylinder head cover includes a labyrinth oil separator. Camshafts are fully assembled and chain-driven. Exhaust valves are sodium-filled to reduce temperature.

Diagram of the cylinder head, showing cylinder head cover, Hall sender, fully-assembled camshaft, and high-pressure fuel pump.

Camshaft Adjustment System

The camshaft adjustment system influences gas exchange for optimal output, torque, and emissions. It uses continuously variable vane adjusters, allowing up to 42° adjustment. Four Hall senders detect camshaft positions. Vane adjusters are mechanically locked when the engine is stationary. Inlet camshafts are set to "retarded," and exhaust camshafts to "advanced," using a return spring in the exhaust camshaft adjusters.

Diagram of the camshaft adjustment system, showing inlet and exhaust adjusters with return spring.

Oil Supply

The oil supply system prioritizes low oil throughput. Camshaft adjusters and friction bearings are optimized. Oil throughput is 50 l/min at 7000 rpm and 120°C. This design allows for better oil degasification and the use of a smaller oil pump, reducing power consumption and fuel use. A baffle plate prevents foamed oil from entering the system. An oil-water heat exchanger cools the oil.

Diagram illustrating the oil supply system, including oil cooler, chain tensioner, oil filter module, oil pump, oil sump sections, oil pressure control valve, and circulation pump.

Oil Pump

The oil pump is mounted inside the oil sump upper section, bolted to the ladder frame. Intake occurs via a base filter and the engine's return duct. All lubrication points are supplied from the pressure oil side.

Diagram showing the oil pump's pressure oil side and base filter suction side.

Oil Filter Module

The oil filter module is a main flow filter located in the engine's inner V for easy maintenance. The filter element, a polymer mat, is exchangeable without special tools.

Diagram of the oil filter module, showing the filter element, cap, and connections.

Crankcase Breather and Ventilation System

Crankcase Breather System

The crankcase breather system flushes fresh air through the crankcase to remove water vapour and low-boiling hydrocarbons, preventing oil contamination. Air is drawn from downstream of the air filter, guided via a non-return valve into the cylinder block's inner V. A restrictor controls the fresh air supply quantity.

Crankcase Ventilation System

Uncombusted hydrocarbons (blow-by gases) are returned to combustion via the crankcase ventilation system. Oil in blow-by gases is separated by a labyrinth oil separator in the cylinder head cover and a three-stage cyclonic micro oil separator. Impact plates in the head cover separate larger droplets, while the micro oil separator removes smaller ones, preventing inlet valve coking. The induction point is integrated into the cooling circuit to prevent freezing.

Diagram of the crankcase breather system, showing vent line, cooling circuit connection, micro oil separator, pressure limiting valve, and non-return valve.

Three-Stage Cyclonic Micro Oil Separator

The separation of hydrocarbons and oil vapour depends on engine load and speed. The micro oil is separated via a three-stage cyclonic system, with one, two, or three cyclones used in parallel based on gas throughput.

Low Engine Load/Speed – Low Gas Throughput

At low load/speed, gas flows to the first cyclone. Centrifugal force separates oil, which collects in the oil collection chamber. An oil drain valve, closed by crankcase pressure during operation, opens when the engine is off, draining oil to the sump. A pressure control valve maintains pressure and crankcase ventilation.

Diagram of the micro oil separator in low gas throughput mode, showing control plunger, pressure control valve, oil collection chamber, and oil drain valve.

Increasing Engine Load/Speed – Increasing Gas Throughput

Higher load/speed increases blow-by gas flow. Increased force on the control plunger overcomes spring force, opening access to additional cyclones.

Diagram showing the control plunger shifted in the micro oil separator.

Bypass Valve Opens – Very High Gas Throughput

The bypass valve prevents excessive crankcase pressure. If pressure rises rapidly (e.g., due to a jammed plunger or piston ring flutter), cyclones cannot cope. The bypass valve opens, directing some blow-by gases directly to the intake manifold via the pressure control valve.

Diagram showing the bypass valve open, with gases flowing past the cyclones.

Cooling Circuit

The cooling system is longitudinal. Coolant flows into the intake side, through the cylinder head gasket, into the head, and out via the timing chain cover. Cylinder web cooling is enhanced by drilled ducts with optimized cross-sections. Forced flow is ensured by sealed water ducts. The system is electronically controlled. Coolant temperature is regulated to 105°C in partial load ranges (offering ~1.5% fuel saving) and 90°C in full load ranges for better combustion and reduced knocking tendency.

Diagram of the cooling circuit, showing expansion tank, oil cooler, alternator, coolant pump, radiator, circulation pump, heating system heat exchanger, coolant distributor, and temperature senders.

Fuel System

The fuel system is requirement-controlled, meaning the electronic fuel pump and two high-pressure pumps deliver only the required fuel, reducing power needs and fuel consumption. It comprises a low-pressure system (up to 7 bar, electronic pump) and a high-pressure system (25-105 bar, mechanical pumps driven by inlet camshafts). To minimize pulsations, high-pressure pumps deliver fuel to a common line, with offset delivery timing.

Diagram of the fuel system, showing high-pressure fuel pumps, fuel metering valves, injectors, fuel rails, pressure limiting valve, fuel pressure senders, fuel filter, and fuel tank.

Exhaust System

The exhaust system has a twin-branch design, with each cylinder block having a separate tract. Exhaust manifolds are insulated sheet metal with a gas-tight inner shell and air-gap insulation for compact design and fast heating. Two broadband and two transient lambda probes are used. Starter and main catalytic converters use ceramic substrate. Both tracts lead to a front silencer where sound waves overlap, reducing noise. Two pipes lead to the rear silencer. Both silencers function as absorption silencers. Exhaust gas exits via two tailpipes.

Diagram of the exhaust system, showing exhaust manifold, lambda probes, starter and main catalytic converters, front silencer, and rear silencer.

Secondary Air System

The secondary air system injects air downstream of the exhaust valves to aid oxidation (afterburning) of hydrocarbons and carbon monoxide during cold-starting and warm-up, helping catalytic converters reach operating temperature faster. It consists of a secondary air pump relay, motor, and two self-opening combination valves. Input signals include lambda probe signals, coolant temperature, and air mass meter load signals.

Diagram of the secondary air system, showing connection on the air filter, secondary air pump, and combination valves.

Secondary Air Injection

The system activates during cold-starting, warm-up, and for EOBD tests. The engine control unit actuates the pump via the relay. Pressure at the combination valves opens them, allowing air injection for afterburning.

Function of the Combination Valves

Combination valves are self-opening, actuated by secondary air pump pressure. When closed, pressure equals ambient. When open, pressure from the pump acts on the diaphragm, opening the valve disk to allow air flow.

Diagram showing a combination valve in the closed state.

Diagram showing a combination valve in the open state.

Engine Management

System Overview

Sensors

Lists various sensors used in the engine management system, including Air mass meters, temperature senders, speed sender, position senders, Hall senders, throttle valve module, flap potentiometers, fuel pressure senders, knock sensors, and lambda probes. Also includes brake switches and sensors.

Diagram showing the engine control unit (J623) connected to various sensors via the CAN data bus.

CAN Networking

Illustrates the communication network between the engine control unit (J623) and other control units (e.g., ABS, gearbox, airbag, climate control, steering column electronics) via CAN data buses.

Diagram showing the CAN networking architecture with various control units and their connections.

Hot Film Air Mass Meter G70 with Intake Air Temperature Sender G42 and Hot Film Air Mass Meter 2 G246

Two hot film air mass meters (G70, G246) and an intake air temperature sender (G42) are used in the twin-branch intake tract for accurate air mass and temperature measurement. Signals are used for load/speed-dependent functions like injection timing and ignition timing. Failure results in substitution values or correction values from other sensors.

Diagram showing hot film air mass meter G70 with intake air temperature sender G42 on cylinder bank 1, and hot film air mass meter G246 on cylinder bank 2.

Hall Sender G40, G163, G300, G301

Hall senders (G40, G300 on bank 1; G163, G301 on bank 2) detect camshaft positions for adjustment, injection point, and ignition timing. Failure prevents camshaft adjustment, but the engine can still run, albeit with reduced torque and power.

Diagrams showing Hall senders G40, G300, G163, and G301 on the cylinder heads.

Fuel Pressure Sender for Low Pressure G410

Located in the low-pressure fuel system supply line, it measures pressure and signals the engine control unit, which regulates the electronic fuel pump. Failure leads to regulation by a pilot control system, maintaining ~6.5 bar.

Diagram showing the fuel pressure sender for low pressure G410.

Fuel Pressure Sender, High Pressure G247

Located in the cylinder block's inner V, connected to the fuel rail, it measures high-pressure fuel. The ECU uses this to regulate pressure via fuel metering valves. Failure results in emergency mode with low fuel pressure, reduced power, and torque.

Diagram showing the fuel rail and the high-pressure fuel sender G247.

Intake Manifold Flap Potentiometer G336 and G512

These potentiometers are secured to the intake manifold and connected to the flap shaft, detecting flap positions. Flap position is critical for airflow and mass, affecting exhaust gas. Signals are used for ignition timing. Failure leads to substitute values, reduced power/torque, and increased fuel consumption.

Diagrams showing potentiometers for intake manifold flaps G336 and G512.

Actuators

Fuel Pump G6

The electronic fuel pump and filter form a fuel delivery unit in the fuel tank. It delivers fuel to the high-pressure pump, controlled by a PWM signal from the fuel pump control unit. It supplies the exact fuel quantity required. Failure stops engine operation.

Diagram showing the fuel pump G6.

Fuel Pump Control Unit J538

Mounted under the rear seat bench, it receives signals from the ECU and controls the fuel pump via PWM. It regulates low-pressure fuel system pressure between 5 and 7 bar. Failure stops engine operation.

Diagram showing the fuel pump control unit J538.

Fuel Metering Valve N290 and N402

Located at the sides of the high-pressure fuel pumps, these valves ensure the correct fuel quantity is available at the required pressure in the fuel rail. If currentless, the regulating valve opens, preventing high pressure buildup and resulting in significantly reduced output and torque.

Diagram showing fuel metering valves N290 and N402.

Inlet Camshaft Control Valve 1 and 2 N205 and N208; Exhaust Camshaft Control Valve 1 and 2 N318 and N319

These solenoid valves on the cylinder head covers distribute oil pressure to camshaft adjusters based on direction and travel. Camshafts are infinitely adjustable (42° crank angle for inlet/exhaust, 47° max overlap). The exhaust camshaft is mechanically locked when oil pressure is absent. Failure leads to no further adjustment, reduced power, and torque.

Diagrams showing inlet camshaft control valves N205, N208 and exhaust camshaft control valves N318, N319.

Variable Intake Manifold Motor V183

Bolted to the intake manifold, this motor is actuated by the ECU based on load/speed to control change-over flaps between torque and output positions. Failure prevents change-over, leaving the manifold in its last position, reducing power and torque.

Diagram showing the variable intake manifold motor V183.

Intake Manifold Flap Motor V157

Bolted to the variable intake manifold, this motor is actuated by the ECU based on load/speed to adjust intake manifold flaps via operating rods. Flaps close intake port sections, creating cylindrical air movement for better mixture formation. Failure prevents flap actuation, leading to poor combustion, reduced output/torque, and increased fuel consumption.

Diagram showing the intake manifold flap motor V157.

Functional Diagram

Detailed electrical schematic diagrams illustrating the engine control system, including components like battery, fuses, relays, sensors, actuators, injectors, ignition coils, and CAN data bus connections.

Diagram showing the functional diagram of the engine control system.

Diagram showing further details of the functional diagram, including sensor and actuator connections.

Diagram showing further details of the functional diagram, including CAN bus connections.

Diagram showing further details of the functional diagram, including CAN bus connections and various control units.

Service

Special Tools

A table lists special tools required for specific service procedures:

Test Yourself

Questions to test understanding of the engine's design and function:

1. How are the camshafts driven?
   • a) Via a toothed belt drive.
   • b) Via an individual roller chain from the crankshaft.
   • c) From the crankshaft, a roller chain drives two drive chain sprockets for the camshaft timing chains. In turn, these drive the camshafts via one chain each.
2. How is intake manifold change-over carried out?
   • a) Intake manifold change-over is carried out via a vacuum unit.
   • b) Intake manifold change-over is carried out via a variable intake manifold electric motor.
   • c) Intake manifold change-over is carried out via a Bowden cable.
3. Which statement on the high-pressure fuel pumps is correct?
   • a) Each of the two high-pressure fuel pumps delivers to one cylinder bank.
   • b) Both high-pressure fuel pumps deliver the fuel jointly to both fuel rails.
   • c) One or both high-pressure fuel pumps deliver fuel depending on engine load and speed.
4. Which statement on the cooling system is correct?
   • a) It is an electronically controlled cooling system with a thermostat for map-controlled engine cooling.
   • b) It is a dual-circuit system with different cooling temperatures in the cylinder block and cylinder head.
   • c) It is an unregulated system with constant coolant temperatures.

Answers: 1. c, 2. b, 3. b, 4. a