Re: Thermal time switch

[steveb@newkla.kla.com (Steven Buchholz)]

> Based on your kind and knowledgable responses concerning cold starting
> problems with my '86 5000cstq along with readings from the Bently Audi
> manual and a few references on Bosch injection, I have concluded that the
> crux of my problem is the thermal time switch.  The problem is, the
> suppliers I've contacted don't carry it (they say it's a dealer only item)
> and my local dealer doesn't know what I'm talking about when I ask for a
> thermal time switch.
> 
> Does anyone know if this is a Bosch part on my make and model (Mfg date
> 3/96)?  There is a chance I can do an end around the "dealer only" dilema
> with a Bosh (or VDO or Motorola or ?) part number.  Can anyone give me a
> more discriptive location?  The pictures I have from the manuals show one
> electrical connection.  Is this accurate?  The dealer is asking for the
> collor of the sensor.  I assume there is a collored plastic band or
> insulator on it.  Any clues?  
> 
Most references I know of call it a thermo-time switch.  This may be where 
the confusion arises, but I would think that the dealer would be familiar 
with the term.  I don't have the 5k Bentley with me, but the 4k/Coupe manual 
shows the switch in every schematic (which does include the newer turbo 
quattro).  The unit gets ground through the engine, and has *two* terminals, 
one for a heater and the other for the switch.  Ideally the thermo-time 
switch allows the cold-start injector to run for 2-3 seconds after the 
ignition switch is turned to the start position when the engine is cold.

I don't know how much troubleshooting that you have done so far, but I would 
recommend that you check the wiring before replacing the switch.  My '78 Fox 
has had problems with cold starting twice, and today it is running with a 17 
year old thermo-time switch.  In that car the harness for the switch came 
into contact with the hood, which led to both wires breaking eventually.  In 
one instance the wire to the heater broke, which left the cold-start injector 
on constantly whenever the starter was engaged and the engine was cold.  The 
engine would not start because it was flooding ... In the other case the 
switched line to the cold-start injector opened so there was never any aux-
iliary fuel and the engine never got enough gas ...

I haven't looked into the location on the 5k, but it should be somewhere 
near the location where the coolant line from the head to the radiator is
located ... look at the wiring diagram for you car to see the colors of the
wires (RED/BLK & GRN/WHT seems to be fairly common) and then find those
wires in the engine compartment ...

Good luck!
Steve Buchholz
s_buchho@kla.com