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Thermo Switch
Posted by loyr (more from loyr) on Sun, 29 Oct 2000 14:19:01
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

I have a cold-running problem with an '85 900S 8-valve (K-jet
w/lambda).  It surges and almost conks out every ~5 seconds.  This
seems to be caused by the FI going closed-loop as soon as the O2
sensor is hot enough, even if the engine is still stone cold.  So I
looked for the thermoswitch that controls the open/closed loop
transition but the thermoswitches in the car do not match the
description in the Bentley...

What I have:

   thermo-time switch (TTS) on head bet cyl 2 & 3
     wires: green and red
     functions correctly

   white-top switch on head just below thermo-time switch
     wires: blue-white and green (or possibly faded blue)
     open when cold; closed when hot

   black-top switch on protrusion of thermostat housing 
     wires: green and green
     closed when cold; open when hot

The wire colors on the TTS do not match the wiring diagram, and I
cannot determine what the white switch is for.  The black-top switch
seems to be 'Thermoswitch I' which is in series with the TTS, and
wire colors match the schematic.

The book shows a 'Thermoswitch II' on the thermostat housing - which I
do not have, but there is a plug screwed in there.  There is a pair of
dangling wires from the harness that are black and red (or maybe orange).
Connecting them has no effect on the freq valve dwell, so either
they are meant to be unused or the harness has rotted.

I noticed on the wiring diagram that the thermo switch controlling
open/closed loop operation grounds terminal X1 of the decel relay.  If
I wire a test lead to ground this terminal, it does in fact lock the
freq valve dwell as it is supposed to.

So the question is, where is my missing thermoswitch, and
what is the white-topped one for?


Any help greatly appreciated,
Ray
'85 900S
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