MB Engine, Waste Gate Hose routing

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

Phil,

Regarding your comment below:

>Phil said:
>There's a subtlety that no one at Audi has been able to explain to me -
>in the earlier MBs, one line goes to unthrottled air, i.e., intercooler
>output.  On the later ones, it goes to throttled air, i.e., the inlet
>manifold. Anyone know why this change was made?

In the US in 1989 there was a "GH" recall campaign for the 1984-85 1/2 KH
engines, the 1985 1/2 to 1986 1/2 MC engine, and the 1986-89 MC engine
vehicles  to reduce the chance of a fire under the hood due to leaky fuel
injector seals. 

This GH campaign involved changing the hood insulation, the valve cover,
pressure testing the air shrouded injector inserts, installing new Viton
fuel injector seals, installing a rubber cover over the fuel injector
lines/fuel distributor and  modifying the vacuum hose routing to the Waste
Gate solenoid and to other components. If the GH recall was done, there
should be a new sticker under the hood #034-010-102L on the plastic
radiator shroud showing the revised vacuum hose routing. 

The GH recall handbook from Audi shows the original WG solenoid lower hose
connection  going to the pre-throttled intercooler exit pressure tap (small
fitting) at the back of the intake manifold. 

In the MC engine intake manifold there is an internal pipe that runs from
ahead of the throttle plate and straight to the back of the intake manifold
where it connects to the idle stabilizer and the hose to the lower waste
gate diaphragm.If you pull off the accordion hose you can see this pipe,
that is the reason the accordion hose has the oval shape. 

The GH recall involves capping off this pre-throttle port at the back of
the intake manifold and re-routing the lower waste gate hose to the intake
manifold metal pipe with three hose fittings to get intake manifold
pressure instead of getting pre-throttle boost pressure. 

The specific reasoning behind the change in hose routing for the waste gate
solenoid is unclear to me other than the overall change to reduce the
possibility of a fire under the hood. 

Below is a copy of the recall notice from the NHTSA site.
http://www.nhtsa.dot.gov/

HTH
Scott

Recall number: 89V006000

Component: FUEL:FUEL SYSTEMS
Manufacturer: VOLKSWAGEN OF AMERICA,INC
Year: 1986
Make: AUDI
Model: 5000
Year of Recall: '89
Type of Report: Vehicle 
Potential Number of Units Affected: 35000
Summary:
FUEL INJECTION SEALS MAY HARDEN, DUE TO HIGH TEMPERATURE AND ALCOHOL IN SOME
FUELS, AND ALLOW FUEL TO ESCAPE INTO THE ENGINE COMPARTMENT.

FUEL DRIPPING ONTO HOT ENGINE COMPONENTS COULD CAUSE AN ENGINE COMPARTMENT
FIRE.

REPLACE ENGINES FUEL INJECTOR SEALS WITH IMPROVED SEALS PLUS IMPROVEMENTS
DESIGNED TO BETTER INSULATE THE ENGINE AGAINST FIRE RISK.

SYSTEM: FUEL

VEHICLE DESCRIPTION: PASSENGER CARS WITH TURBO.