Thermo Time Switch/ Cold Start Valve Question

[Steve F]

A few questions if I may....

1981 SC not starting, fires if I spray starter fluid in the POV port. Both yellow wires on starter good . With CDI disconnected and test light on yellow wire and ground on the TTS , crank over I get voltage.

I disconnected connector at CSV and inserted modified spade connectors in the socket, hooked to test light, crank over,...No voltage

Can I jumper the TTS and try again to prove the TTS bad?
Is the TTS a common part to other CIS systems, Volvo, Mercedes,(junk yard) or specific to the 911?

The TTS yellow post reads 24 ohms to ground , the other post reads grounded, also 24ohms post to post.


Thanks for any suggestions,Steve

[Bob Kontak]

TTS is the caboose in the system.

I am going to say some stuff you probably already know so just roll with it.

Starter -> CSV -> TTS-> ground.

Crank starter. Juice goes thru CSV and is at TTS asking if it can go to ground. If 25C TTS says, Hell yes, come on thru. At 36C the door is closed.

I would take the yellow wire at the TTS and alligator clip it to ground. Bypasses the TTS but will only be "live" when the starter is cranking.

[dhanl82]

I may be mistaken but when I was having the same problem and wanted to determine if the TTS was working, in order to bypass it, I grounded the red/black TTS wire which comes from the CSV looking for ground. I believe the yellow TTS wire powers the heater in the TTS that limits - through the TTS- the CSV to a max run time of 8 seconds - under the coldest conditions - so as not to flood the engine.
In addition, if no power at CSV it could be not getting current through the yellow wire coming from the starter.

Just my thoughts, certainly not the expert!

Dave

1982SC

[gomezoneill]

The CSV get's power every time you try to start the car. The CSV needs a ground to operate. It get's it's ground from the thermo time switch when the temperature is low enough to need the extra fuel. The yellow wire (coming from the starter) on the thermo time switch applies power to the switch heats a bimetallic spring inside and breaks the ground after 8 seconds of cranking. So you see, the cold start valve is controlled by ground not power like most circuits.

[Steve F]

Than you all for your input ! Perhaps putting a lead in each socket of the CSV cable was not the right way to verify that is was receiving power? No ground? I'm more of a nuts and bolts guy , trying to absorb this


Thanks again!

[Bob Kontak]

Originally Posted by gomezoneill

The yellow wire (coming from the starter) on the thermo time switch applies power to the switch heats a bimetallic spring inside and breaks the ground after 8 seconds of cranking. So you see, the cold start valve is controlled by ground not power like most circuits.

Where is the ground? Does it return to the CSV via the non-yellow wire to ground somewhere else or is the ground made at the TTS where it mates to engine? Or other?

I am subscribed.

Steve, resistance on my 81's TTS is 24.9 ohms.

[Steve F]

Thanks Bob! Sounding like the TTS maybe OK? Looking forward to understanding this critter

[ossiblue]

Originally Posted by Bob Kontak

Where is the ground? Does it return to the CSV via the non-yellow wire to ground somewhere else or is the ground made at the TTS where it mates to engine? Or other?

I am subscribed.

Steve, resistance on my 81's TTS is 24.9 ohms.

The ground comes from the TTS. Inside the switch, the power terminal is connected by a wire to a contact point affixed to the bottom of the metal tube of the TTS body. This contact is grounded to the engine via the threads holding the TTS into the case. The wire to this fixed contact also makes up the heating element that is wrapped around a bimetallic strip which is connected to the ground terminal of the TTS. The tip of this bimetallic strip, when cold, touches the fixed ground point and is, therefore grounded as well. The ground lead to the CSV is connected to the terminal of the bimetallic strip so, when the engine is cold, the CSV is grounded. As the engine is cranked, voltage flows to the TTS terminal connected to the fixed ground, heating the element on the bimetallic strip, and after approx. 8-10 seconds, causes the strip to bend, breaking the ground contact with the fixed point. No ground is provided to the CSV once the points are separated either by heat from continued cranking or heat sink from the engine.

Click link,for a diagram.

Thermo Time Switch 1978 SC 3.0

[boyt911sc]

Larry,

Thanks for the link. I am not computer savy like most of you and I could hardly locate my old posts in this forum.

Tony