The following is a copy of the original VR6 tech manual, with notes where applicable.
Self-Study Program 402
Volkswagen of America, Inc.
Printed in U.S.A.
Part # WSP 521-402-00
All rights reserved. All information contained
in this manual is based on the latest product
information available at the time of printing.
The right is reserved to make changes at any
time without notice.
Always check Technical Bulletins and the mirofiche
system for information that may supersede any
information included in this manual.
*** Introduction ***
Volkswagen has developed a new six-cylinder engine called the VR-6.
This 2.8-liter engine is unique in that the V-angle between cylinder
banks is 15° rather than the 60° or 90° found in most conventional
V-6 engine designs.
The engine features a cast-iron crankcase, one light alloy crossflow
cylinder head with two valves per cylinder operated by chain-driven
All fuel and ignition requirements of the VR-6 engine are controlled
by the Bosch Motronic M2.9 Engine Management System.
This Engine Management System features an air mass sensor, dual knock
sensors for cylinder-selective ignition knock regulation, and Lambda
Exhaust gases are channeled through a 3-way catalytic converter.
*** Engine Specifications ***
Engine code: AAA
Design: Four-stroke, internal combustion engine in "Vee"/in-line
Displacement: 2.8 liter
Bore diameter: 81.0 mm
Stroke: 90.0 mm
**note this is listed as 90.3mm elsewhere
"Vee" angle: 15°
Compression ratio: 10:1
Fuel and ignition systems: Bosch Motronic M2.9
Emission control: Lambda control with catalytic converter
The name, VR-6 come from a combination of Vee and the German word
Reihenmotor. The combination of the two can be roughly translated
as "in-line Vee."
Volkswagen has designed the 15° VR-6 to take advantage of
conventional in-line six-cylinder engine features (single cylinder
head, narrow width and excellent balancing) with the advantages
of a V-6 engine design (short overall length and compactness).
*** VR-6 ***
The VR-6 was specifically designed for transverse installation
in front-wheel-drive vehicles. By using the narrow 15° VR-6 engine,
it was possible to install a six-cylinder engine in existing
*** V-6 Conventional Design ***
A wider V-6 engine of conventional design would have required
lengthening existing vehicles to provide enough crumple zone
between the front of the vehicle and the engine, and between
the engine and the passenger cell.
Using the narrow VR-6 engine will help Volkswagen meet current
and future front-end crash standards.
*** Overview ***
The drop-forged steel, six-throw crankshaft runs in seven main
bearings. The connecting rod journals are offset 22° to one
Overhead camshafts (one for each bank of cylinders) operate the
hydraulic valve lifters which, in turn, open and close the 39.0-mm
intake valves and 34.3-mm exhaust valves.
Because of the special VR-6 cylinder arrangement with two rows
of combustion chambers in the same cylinder head, the intake
runners between the two cylinder banks are of varying lengths.
The difference in intake length is compensated in the overhead
intake manifold. Each runner is 420 mm long.
Exhaust gases are channeled from two 3-branch cat-iron exhaust
manifolds into a sheathed Y-pipe. From there, they are channeled
into a single flow before passing over the heated Oxygen Sensor
and then to the catalytic converter.
The oil pump driveshaft is driven by the intermediate shaft.
Fuel injectors of the Bosch M2.9 Engine Management System are
mounted behind the bend of the intake manifolds. Besides being
the optimum location for fuel injection, this location also helps
shield the injectors during a frontal impact.
The water pump housing is cast integral with the engine crankcase.
In addition to the belt-driven water pump, VR-6 engine will use
an auxiliary electric pump to circulate water while the engine is
running and during the cooling fan after-run cycle.
In the interest of environmental friendliness, a replaceable oil
filter cartridge is used on the VR-6 engine.
The sump-mounted oil pump is driven via the intermediate shaft.
An oil pressure control valve is integrated in the pump.
*** Crankcase ***
The crankcase is made from Perlitic gray cast iron with micro-alloy.
Two banks of three cylinders are arranged at a 15° axial angle from
The cylinder bores are 81 mm in diameter with a spacing of 65 mm
between cylinders. They are staggered along the length of the
engine block to allow the engine to be shorter and more compact
than conventional V-6 engines.
The centerline of the cylinders are also offset from the centerline
of the crankshaft by 12.5 mm.
To accommodate the offset cylinder placement and narrow "Vee"
design, the connecting rod journals are offset 22° to each other.
This also allows the use of a 120° firing interval between cylinders.
The firing order is: 1, 5, 3, 6, 2, 4
*** Cylinder Head ***
The aluminum crossflow cylinder head is manufactured in a permanent
mold casting. The combustion-chamber side of the head is hardened
through a separate chill casting
Twenty stretch bolts are used to retain the cylinder head to the block.
These bolts are accessible even with the camshafts installed.
However, it is necessary to retorque the bolts after installation.
Holes for bolts, numbers 12 and 20 are sleeved to make cylinder head
To help optimize flow through the cylinder head, the area above the
valve seats has been machined. Valve shaft diameter has been reduced
to 7.0 mm during development.
Cylinders 1, 3, and 5 have short intake runners and long exhaust
runners while cylinders 2, 4, and 6 have long intake runners and
short exhaust runners.
A crossflow cylinder head has allowed the use of a single cylinder
exhaust manifold rather than a manifold for each bank.
*** Combustion Chamber ***
The surface of the combustion side of the cylinder head is flat.
The combustion chamber is formed by the shape of the piston head.
Ten different piston designs were tested during development of the
The result of these tests was the selection of a slanted piston
head within eccentric trough. The trough is offset from the center
of the piston by 4.0 mm.
Compression gap height (at TDC) is 1.5 mm. the compression ratio is
*** Chain tensioners ***
Operated by oil pressure and spring tension.
The camshafts are driven by a two-stage chain-drive system located
on the flywheel side of the engine.
Chains were selected to drive the valve train in consideration of
a Diesel version of the VR-6 engine.
A single chain (lower) is driven by the crankshaft which, in turn,
drives an intermediate sprocket and shaft at a ratio of 3:4.
The intermediate shaft sprocket drives the camshafts via a double
roller chain (upper) at a ratio of 2:3. A double roller chain is
used to drive the camshaft sprockets because it must transfer more
torque than the lower chain.
The specific gear ratio selection was chosen in order to keep the
camshaft sprocket size small. This helps keep the overall engine
height to a minimum.
Chain tension is maintained by two chain tensioners. The upper
chain tensioner is hydraulically operated by engine oil pressure
and spring tension.
The lower chain tensioner (with mechanical lock) is operated by
spring tension and lubricated with engine oil.
Chain flutter is prevented by guide rails on the slack side of
*** Engine Cooling System ***
The VR-6 Engine uses an impeller-type water pump driven by the
The pump housing itself is cast into the engine block adjacent
to cylinder number 2.
In addition, an Auxiliary Electric Coolant Pump also circulates
engine coolant anytime the ignition is switched on.
The Auxiliary Electric Coolant Pump also runs when the engine
is switched off and the coolant temperature goes over 107° C (220° F).
It runs in conjunction with the Radiator Cooling After-run System.
Circulating the coolant during this time helps cool the engine
block and prevent the possibility of air pockets forming in the
The thermostat housing of the cooling system also houses the
temperature senders G2, and F87 for the Radiator Cooling After-run
System, and temperature sender G62 for the Motronic Engine Management
*** Intake Manifold ***
Volumetric efficiency must be uniform to attain smooth engine
running and optimal power output under all operating conditions.
This, in turn, requires identical flow conditions in the intake
ports of all cylinders.
Since the lengths of the intake runners in the VR-6 cylinder head
are not equal, it was necessary to compensate with the internal
design of the intake manifold.
All air intake passages are 420 mm long.
*** Auxiliary Drives ***
A double-sided poly-ribbed belt drives all the auxiliary components
of the VR-6 engine.
A spring-operated tensioning roller keeps the poly-ribbed belt at
the proper tension. The belt tension is released by threading a
long 8 mm bolt into a threaded hole on the tensioner.
*** System Overview ***
The VR-6 engine will use the Motronic Engine Management System
All Corrados will have EGR while only California-version Passats
will have EGR.
*** Fuel Delivery System ***
A two stage fuel pump supplies fuel through the filter to the fuel
manifold and the four hole injectors. The pump is located in the
The fuel manifold is located on the intake manifold. A fuel pressure
regulator is attached to the fuel manifold on the fuel return side.
The fuel pressure regulator is a diaphragm-type regulator. Fuel
pressure is regulated depending on intake manifold pressure.
As intake manifold pressure changes, the pressure regulator will
increase or decrease the system fuel pressure. This maintains
constant pressure differences between the intake manifold pressure
and fuel pressure.
*** Two-Stage Fuel Pump ***
The two-stage pump has one motor that drives two separate pumps.
* Stage One *
Fuel is drawn in through a screen at the bottom of the housing
by a vane-type pump. The vane-type pump acts as a transfer pump.
It's designed to supply fuel to the fuel accumulator which is
within the pump housing.
Fuel vapors and air bubbles from fuel returning from the engine,
as well as excessive fuel, is forced out of the accumulator through
a fuel vent.
* Stage Two *
The gear-type pump draws fuel in from the bottom of the accumulator
and through a screen. The fuel is then forced through the pump
housing by the gear pump and out the top.
*** Fuel Injectors ***
The injectors are supplied 12 volts by the Power Supply Relay and
are grounded through the Motronic ECU. They are opened sequentially
in the cylinder firing order.
Injection quantity is determined by the injector opening time.
*** Fuel Tank Ventilation ***
The following inputs are used to control the fuel tank ventilation:
.Engine coolant temperature
.Signal from throttle valve Potentiometer (G69)
Fuel vapors from the fuel tank are vented to the carbon canister.
When the engine is warm and above idle speed, the vapors will be
drawn into the intake manifold via the carbon canister.
Depending on engine load and oxygen sensor signal, a frequency valve
will regulate the quantity of vapors entering the intake manifold from
the carbon canister
* Carbon Canister Frequency Valve (N80) *
The ECU determines the duty cycle of the frequency valve to regulate
the flow of fuel vapors from the carbon canister to the engine.
When no current is supplied to the valve, it remains in the open
The valve is closed (duty cycle 100%) when the cold engine is started.
* Triggering: *
The Carbon Canister Frequency Valve (N80) begins to operate after
oxygen sensor operation has begun.
Valve operation is load- and speed-dependent during driving operation.
The valve is completely open at full throttle and completely closed
during deceleration fuel shut-off.
* Substitute function: *
If power to the valve is interrupted, the valve remains completely open.
This could lead to rough running at idle speed and during partial load
* Self-diagnosis: *
The ECU recognizes open circuits and short circuits in the component.
*** Air Mass Sensor (G70) ***
A hot-wire air mass sensor is used to measure the airflow into the
engine. The air mass sensor is attached to the air filter housing.
The sensor housing includes a baffle grid which reduces air turbulence
and pulses. The sensor has no moving parts.
A thin, electrically-heated , platinum hot-wire in the sensor is kept
180°C (356°F) above the air temperature measured by the thin-layer
platinum temperature sensor.
As airflow increases, the wires are cooled and the resistance of the
sensors changes. Current to the platinum hot-wire changes to maintain
the constant temperature difference.
The resulting current change is converted to a voltage signal and is
used by the Motronic ECU to calculate the volume of air taken in.
Dirt or other contamination on the platinum wire can cause inaccurate
output signals. Because of this, the platinum wire is heated to 1000° C
(1832° F) for a period of one second each time the engine is switched
off to burn off this dirt or contamination.
If a fault develops with the signal from the air mass sensor, the signal
from the throttle potentiometer is used as a substitute in order for
the car to remain derivable.
[Modified by Boost Inside, 6:48 AM 3-4-2003]
[Modified by Boost Inside, 6:50 AM 3-4-2003]