Re: 91 200qw hose replacement/boost problem

["Scott M." <scottmo@teleport.com>]

> Subject: Re: 91 200qw hose replacement/boost problem
> Date: Friday, August 29, 1997 12:26 PM
> 
> Ed Kellock wrote:
> 
> > Question: On the 3B engine, if I pull the dipstick or
remove the oil filler cap,
> > should it stall or not?

Igor responded:
> No, it should not. Your car's fuel distributor measures
the amount of air, that enters 
> the intake by a *hot wire* method. Unlike earlier CIS
cars (like mine), your's is not 
> vacuum dependent.

Scott adds:
Well, the 3B uses a different crankcase breather system and
this is more likely the reason the car does not stall if
the oil filler cap or dipstick is removed. The 3B has
pressure regulator valve at the rear of the engine where
the crankcase breather hose connects to the pipe that runs
up to the turbo intake boot. These have been known to be  a
problem on the 3B. There is also a pressure check valve
where the intake manifold hose connects to the breather
hose on the drivers side  of the engine block. 

The 3B uses the Bosch Motronic fuel/ignition management
system with electronically controlled injectors. The only
fuel distributor on this car is the fuel rail that provides
fuel to these injectors. This rail does not meter the fuel.
The hot wire Mass Air Flow (MAF) sensor responds to the
mass of air flowing into the engine, any "unmetered" air
coming in from a vacuum leak will affect the mixture as the
MAF will not measure this air coming in from the leak. I
would remove all the breather hoses and visually inspect
them for cracks etc. 

Ed asked:
> > Also, this morning I unplugged the throttle position
switch and right off the
> > bat experienced limited boost.

Igor responded: 
> It's because the CIS-E can not sence the WOT condition
with the TPS switch unplugged, 
> hence it does not go into open loop and therefore max
boost is not attainable.

Scott adds:
The 3B does not use the CIS-E system as mentioned above,
the Motronic system uses a combination idle switch and
throttle potentiometer (variable resistor) to more
accurately sense throttle plate position over just using a
WOT throttle switch like what is used on the earlier 10V MC
Audi Turbo engines. Boost regulation on the 3B begins when
the throttle plate is opened greater than 35 degrees. These
potentiometers can be checked for basic operation with a
DMM, typically they connect into the ECU and provide a
voltage divider that produces a voltage that varies
somewhere between 0-5 V. More throttle usually means more
voltage. The Service training booklet for these engines
indicates that a failure of this throttle potentiometer
will result in a boost loss as the boost will be controlled
mechanically by the wastegate diaphragm/spring system.

 A defective air temp sensor,  knock sensor (2), altitude
sensor, multifunction coolant temp sensor, or waste gate
solenoid, can also cause a loss of boost. A few people on
this list have found defective Waste Gate solenoids on
these cars.

Let me know if you want a copy of this service training
information for the 1991 20V 3B engine.

HTH
Scott M.