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Thermo-Time Switch Questions?

Does the Thermo-Time Switch complete the circuit to the Cold Start Valve?

If so, with a faulty Thermo-Time Switch (stuck), would this cause a Rich condition since the Cold Start Valve never closes?

This is on an L-Jet if this matters.

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1981 Porsche 928 "Euro" Auto Gunsmoke Metallic Flat - Black Interior
1983 Porsche 928S "US" Auto Light Bronze (Copper) Metallic - Brown Interior **SOLD**
Old 02-03-2011, 10:06 AM
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Yes and no! According to the diagram, cold start gets its feed from 87 on relay XIV ( starter relay) so it only energises when ignition is in start position.
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Old 02-03-2011, 10:15 AM
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It does cause rich start according to the description of its operation.

As its been explained to me, the switch when operating correctly turns off the valve.
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Old 02-03-2011, 10:33 AM
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I had no start situations when my thermo-time failed on an 84.





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Old 02-03-2011, 10:38 AM
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Yes, I understand the Rich start scenario, but if a Thermo-Time Switch is stuck on and never disconnects, can it potentially keep the Cold Start Valve "On"? Or does the Cold Start Valve have a mechanism to avoid this?

Just thinking out loud. Thanks for those great replies. Keep 'em coming
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1983 Porsche 928S "US" Auto Light Bronze (Copper) Metallic - Brown Interior **SOLD**
Old 02-03-2011, 11:05 AM
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Not sure.

Did you try operating without 02 hooked up?
My 84 automatic operated terribly rich with its O2 sensor. Disconnected it was much better.

Disconnected and it ran great

Switched exhaust and O2, from another car, and richness stayed away but a flat spot transfered with that exhaust and sensor from the donor car onto this subject car.

Disconnected that O2 sensor at it ran great.

New O2 sensor and it also runs great.


So on the same car I feel I saw two different modes of bad operation with different bad O2. sensors
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Last edited by Landseer; 02-03-2011 at 11:44 AM..
Old 02-03-2011, 11:39 AM
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Yes, I think I posted in my 928S thread that I changed out my O2 Sensor and ran the car without and then with the New one installed. It seemed to run less Rich, but not really sure since I don't have any way to Gauge except to go to the Tailpipe and smell.

I could just be paranoid, but I thought while I was in the refresh stage that I would replace this switch too. I don't really want to replace it if it's functioning as it should since it's a $100 part.
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Old 02-03-2011, 11:47 AM
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Quote:
Originally Posted by MPDano View Post
Yes, I understand the Rich start scenario, but if a Thermo-Time Switch is stuck on and never disconnects, can it potentially keep the Cold Start Valve "On"? Or does the Cold Start Valve have a mechanism to avoid this?

Just thinking out loud. Thanks for those great replies. Keep 'em coming
Per the diagram, even if Thermo-Time Switch is stuck on , it will still only pass power to the cold start valve during the start cycle.
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Old 02-03-2011, 12:46 PM
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Quote:
Originally Posted by neil30076 View Post
Per the diagram, even if Thermo-Time Switch is stuck on , it will still only pass power to the cold start valve during the start cycle.
Got it. Start Cycle meaning when the Ignition Switch is full forward to also activate the Starter, but when you let go of key, key goes back a notch and disconnects the circuit to Starter and the Cold Start Valve.

Correct?
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Old 02-03-2011, 12:52 PM
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Quote:
Originally Posted by MPDano View Post
Got it. Start Cycle meaning when the Ignition Switch is full forward to also activate the Starter, but when you let go of key, key goes back a notch and disconnects the circuit to Starter and the Cold Start Valve.

Correct?
Yes, when the Start position is released to RUN the start circuit is no longer in operation, so no juice goes down the Yellow wire start path to Starter or Thermo switch and start valve.
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Old 02-03-2011, 01:16 PM
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Cool, just trying to cover all bases before I go to the Smog Station, which I will time with Neil and do a quick check with his machine on the way. This will also get the car nice and toasty for the test.

As you can see from the 1st posts of this thread, the car was super rich.
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1983 Porsche 928S "US" Auto Light Bronze (Copper) Metallic - Brown Interior **SOLD**
Old 02-03-2011, 03:15 PM
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Leo, just let me know when - i'll have the beast ready!
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81, 86 928 widebody.
1929 Model A Street Rod 270hp, V6
Land Rover Discovery
Bayliner Ciera 2655
Old 02-03-2011, 03:27 PM
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928: Serial Enabler
 
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Just for completeness...may want to print this, FWIW.



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Old 02-03-2011, 04:30 PM
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