ESP BMW 735i 1999 E38 M62TU Engine Workshop Manual

5
BASIC FUNCTION OF BMW VANOS SYSTEMS
All BMW VANOS systems are operated through electric/hydraulic/mechanical control.
Electric Control: The engine control module is responsible for activating a VANOS sole-
noid valve based on DME program mapping. The activation parameters are influenced
by the following input signals:
• Engine speed
• Load (intake air mass)
• Engine temperature
• Camshaft position
• Oil temperature (MS 42.0 only)
Depending on the specific VANOS system, the solenoid valve is one of two types:
• Basic black/white (on/off) solenoid valve. Found on M50 TU and M52 engines.
• Variable position solenoid valve. Found on the M52 TU and M62 TU engines.
Hydraulic Control:The position of the solenoid valve directs the hydraulic flow of engine
oil. The controlled oil flow acts on the mechanical components of VANOS system to
position the camshaft.
Mechanical Control: The mechanical components of all VANOS systems operate under
the same principle. The controlled hydraulic engine oil flow is directed through advance
or retard activation oil ports. Each port exits into a sealed chamber on the opposite sides
of a control piston.
• The control piston on six cylinder engine systems (M50TU, M52 & M52TU) is con-
nected to a separate helical gear cup.
• The control piston on the M62TU VANOS system incorporates the helical gear.
In its default position the oil flow is directed to the rear surface of the piston. This pulls
the helical gear forward and maintains the retarded valve timing position.
When the oil flow is directed to the front surface of the piston, the oil pushesthe helical
gear in the opposite direction which rotates the matched helical gearing connected to the
camshaft.
The angled teeth of the helical gears cause thepushingmovement to be converted into
arotationalmovement. The rotational movement is added to the turning of the
camshaft providing the variable camshaft positioning.

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VANOS SERVICE NOTES
VALVE TIMING PROCEDURES
Refer to TIS for complete Valve Timing Procedures.M62 TU valve timing adjustment is sim-
ilar to the previous non VANOS M62 engine with the exceptionof setting the VANOS
transmissions to their max retard positions with an ohmmeter and attaching the camshaft
gears to each camshaft with single reverse threaded bolts.
• After locking the crankshaft at TDC, the camshaft alignment tools (P/N 90 88 6 112 440)
are placed on the square blocks on the rear of the camshafts locking them in place.
• The exhaust camshaft sprockets and VANOS transmission units with timing chains are
placed onto their respective camshafts.
• The exhaust camshaft sprockets and VANOS transmissions are secured to the
camshafts with their respective single, reverse threaded bolt. Finger tighten only at this
point. Install the chain tensioner into the timing chain case and tension the chain.
• Connect an ohmmeter across two of the three pin contacts on the front edge of one of
the VANOS transmissions. Twist the inner hub of transmission to the left (counter clock-
wise). Make sure the ohmmeter indicates closed circuit. This verifies that the trans-
mission in the default max retard position.
• Using an open end wrench on the camshaft to hold it in place, torque the VANOS trans-
mission center bolt to specification.
CAMSHAFT IMPULSE WHEEL POSITION TOOLS
The camshaft impulse wheels require a special tool set
to position them correctly prior to torquing the retaining
nuts.
The impulse wheels are identical for each cylinder
bank. The alignment hole in each wheel must align
with the tool’s alignment pin. Therefore the tools are
different and must be used specifically for their bank.
The tool rests on the upper edge of the cylinder head
and is held in place by the timing case bolts.
Refer to the TIS repair manual section for complete
information.
BANK I TOOL
BANK I TOOL
BANK II TOOL
ALIGNMENT
IMPULSE

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PWG SIGNAL MONITORING & PWG FAILSAFE OPERATION:
• As a redundant safety feature the PWG provides two separate signals from two integral
potentiometers (Pot 1 and Pot 2) representing the driver’s request for throttle activation.
• If the monitored PWG potentiometer signals are not plausible, ME 7.2 will only use the
lower of the two signals as the driver’s pedal request input providing failsafe operation.
Throttle response will be slower and maximum throttle position will be reduced.
• When in PWG failsafe operation, ME 7.2 sets the EDK throttle plate and injection time
to idle (LL) whenever the brake pedal is depressed.
• When the system is in PWG failsafe operation, the instrument cluster matrix display will
post “Engine Emergency Program” and PWG specific fault(s) will be stored in memory.
EDK FEEDBACK SIGNAL MONITORING & EDK FAILSAFE OPERATION:
• The EDK provides two separate signals from two integral potentiometers (Pot 1 and Pot
2) representing the exact position of the throttle plate.
• EDK Pot 1 provides the primary throttle plate position feedback. As a redundant safe-
ty feature, Pot 2 is continuously cross checked with Pot 1 for signal plausibility.
• If plausibility errors are detected between Pot 1 and Pot 2, ME 7.2 will calculate the
inducted engine air mass (from HFM signal) and only utilize the potentiometer signal that
closely matches the detected intake air mass.
- The ME 7.2 uses the air mass signalling as a “virtual potentiometer” (pot 3) for a
comparative source to provide failsafe operation.
- If ME 7.2 cannot calculate a plausible conclusion from the monitored pots (1 or 2
and virtual 3) the EDK motor is switched off and fuel injection cut out is activated
(no failsafe operation possible).
• The EDK is continuously monitored during all phases of engine operation. It is also
briefly activated when KL 15 is initially switched on as a “pre-flight check” to verify it’s
mechanical integrity (no binding, appropriate return spring tension, etc). This is accom-
plished by monitoring both the motor control amperage and the reaction speed of the
EDK feedback potentiometers. If faults are detected the EDK motor is switched off and
fuel injection cut off is activated (no failsafe operation possible). The engine does how-
ever continue to run extremely rough at idle speed.
• When a replacement EDK is installed, the ME 7.2 adapts to the new component
(required amperage draw for motor control, feedback pot tolerance differences, etc).
This occurs immediately after the next cycle of KL 15 for approximately 30 seconds.
During this period of adaptation, the maximum opening of the throttle plate is 25%.

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ACCELERATOR PEDAL SENSOR (PWG)
The driver's application of the accelerator pedal is monitored by a PWG sensor in the dri-
ver's footwell as with previous non-bowden cable EML systems.
The PWG provides two separate variable voltage signals to the ME 7.2 control module for
determining the request for operating the Electric Throttle Valve (EDK) as well as providing
a kickdown request with automatic transmission vehicles.
The ME 7.2 monitors the changing signal
ranges of both circuits as the pedal is pressed
from LL to VL.
• In vehicles equipped with an automatic transmission (A5S 440Z), the ME 7.2 recognizes
the max pedal value (4.5V) as a kickdown request and signals the AGS via CAN bus.
PWG SIGNAL MONITORING & PWG FAILSAFE OPERATION:
• If the monitored PWG potentiometer signals are not plausible, ME 7.2 will only use the
lower of the two signals as the driver’s pedal request input providing failsafe operation.
Throttle response will be slower and maximum throttle position will be reduced.
• When in PWG failsafe operation, ME 7.2 sets the EDK throttle plate and injection time
to idle (LL) whenever the brake pedal is depressed.
• When the system is in PWG failsafe operation, the instrument cluster matrix display will
post “Engine Emergency Program” and PWG specific fault(s) will be stored in memory.