Thermotime Switch?! Help Me Here....

[Sunroof]

I have been experiencing a cold start problem lately and several folks told me to change the "thermotime switch". Okay, but to my knowledge their is no "thermotime switch" on the 1973.5T CIS! Our host advertises one and even shows its location on the drivers side engine chain cover. It lokks like it replaces onme of the attachment bolts. I have not checked this location as of yet, but when changing out the muffler a few years back, I did not notice any wires or sensor attached to the rear chain cover. I have always known the first CIS (1973.5T) to have a hand throttle, warm up regulator and cold start valve as part of its cold start up system. The hand throttle acts as the "thermotime switch".

Can someone who knows about this please chime in on this one. I say no "thermotime switch" on the 1973.5T-CIS.

Thanks

Bob

[304065]

911 617 117 00 is a temperature switch for the CIS system, it mounts in a threaded boss in the port-side chain cover. The PET diagram shows an MFI-style "thermo time switch" in the illustration, but that's not a CIS component, it's for MFI (think Carrera 2,7).

[Sunroof]

Thanks John, but what your telling me then is that its a "temperature switch" not a "thermotime Switch". I thought the temperature switch mounted into the block under the AC compressor area? Some vendors advertise the "thermotime switch" for the 73.5.

Still confused over this.................

Bob

[304065]

Bob,

There's a temperature SENDER which mounts in the engine case near the starboard cam line. That is for sensing oil temperature.

Distinguish that from the temperature switch which is used as part of the CIS.

CIS Thermo Time Switch ????

[Sunroof]

Got it on the temperature sensor, but...............does the 1973.5T CIS have a "thermotime Switch" ?????????????????????

On the 1974 model, the "thermotime switch" is behind the airbox somewhere.

Bob

[Gunter]

Bob:
On '78-'83 SC's we have:
Thermo Time Switch (TTS) is located (Screwed into) the left chain cover. It has 2 wires on it; 1 comes from the starter Soenoid and energizes the TTS during cranking.
The 2nd wire from the TTS goes to the Cold Start Valve (CSV) to energize it for a few seconds depending on temperature.
There is also a Thermo Time Valve (TTV) on some years looped into the vacuum line from the WUR to the TB and Deceleration Valve.
Not sure when the TTS came into the picture.
How is the CSV actuated on a 1973.5?

[Sunroof]

Not really sure, but the cold start valve is activated and the hand throttle holds open the sensor plate and something magical happens! BAM!!!!!!!

I am confident to 99.999% that a thermotime switch does not exist on the 1973.5T CIS model; however, what had me concerned all of a sudden was the advertising of one for my model and several Porsche nuts advising me of the same.

Still, no one has really has answered the question................

Bob

[Gunter]

Do you see a TTS screwed into the left chain cover?
It's a round plug with 2 wires.
I would start a new thread: Where is the Thermo Time Switch on a 1973.5 CIS?

[304065]

It HAS to have one, a TTS is an integral part of Bosch K-Jet. (CIS).

Take a picture of your left chain cover and post it.

[Sunroof]

I took a look at the left side upper chain cover last night and noticed that where the "thermotime switch" would go (according to the parts schematic) that only a large bolt or plug was found.

The engine was totally rebuilt and the re-builder must have failed to install the "thermotime switch". The rear wiirng harness was completely rebuilt and no additional wires are hanging out anywhere! I have owned this car for eight years now and seldom have I had a cold start issue. I have replaced every CIS component from the airbox/pop-off valve to restoring the fuel tank and new lines aft.

In order to install a thermotime switch, I would have to find where it lies in the wiring diagrams. So, this is a very interesting situation I am confronted with. Have I defied the performance odds by not operating a "thermotime switch" all these years? Does not seem performance has been impacted.

Any ideas?

Bob

[911quest]

Alot of times they are removed or disconnected if they go bad they can cause cranking problem (slow cranking). Also check on the breather cover that it isn't there That is where it is on the MFI cars and some of the later equipped carbed cars. The 73.5 T is kinda of a Bastard car alot of mixing of old and new technology for the time.

[Sunroof]

Right on Tony!

The 73.5T is certainly a pain when matching up parts. More of the dealers and parts vendors tend to move over to the 1974 CIS when matching parts and thats far from correct. Many parts cannot be switched from a later model.

Examples:

Fuel Distributor - the 1974 distributor will not work
Fuel Pump - (only the 1973.5T pump has a built in check valve, all others are
external)
Injectors - they are installed directly into the cylinders not the intake manifolds
as with 1974 on
Warm Up Regulator - Original was very small and luckily the 1974 is a good
retrofit that can be adjusted
Hand Throttle - Gotta love em! Just like the chokes on my Triumph and Austin
Healey

I am sure I am missing more components when specs. are compared, but I have noted over the years thats parts folks do not deal much with the 1973.5T and you have to always make sure they are looking at the right replacement part.

Appreciate the input on the thermotime switch.

Bob

[Gunter]

Originally Posted by Sunroof

I took a look at the left side upper chain cover last night and noticed that where the "thermotime switch" would go (according to the parts schematic) that only a large bolt or plug was found.

That may be the TTS. Post a picture

The rear wiirng harness was completely rebuilt and no additional wires are hanging out anywhere!
Bob

If the harness was rebuild to stock, there should be wires for the TTS somewhere.
Trace the wire from the CSV and see where it ends up.
Look at the starter Solenoid and let us know how many wires you find:
Big black from battery,
Big red from alternator,
Small yellow from ignition switch,
Small wire to TTS or CSV? Do you have a second small wire coming off the Solenoid?

[SC-targa]

I don't see that you should have one, but I just glanced at it.

Jerry

[SC-targa]

[Sunroof]

A bit hard to read the schematics, but it looks like the CIS was not meant to have a thermotime switch, according to the above diagram. Start up for me is simply, pull up the hand throttle, foot off the gas, listen for the CDI for humming and the fuel pump churning and pressurizing the system, turn the key and the flat six sparks off really nice. So how would the thermotime switch come into play here anyways? Where does the cold start valve gets it signal to spray?

Its getting interesting.......but no concensus yet....

Bob

[Mysterytrain]

I found this on Jim's CIS page:

"1974 though 1983 chronology
In '74, with the upgrade to the 2.7 liter engine, several changes were made to the fuel system.

Intake pipes changed from bent tubing to cast intake runners.
Mounting holes for injectors moved from heads to base of intake runners.
Fuel distributor recalibrated for larger 2.7 liter engine.
Deceleration valve recalibrated for larger 2.7 liter engine.
Cold start valve re-positioned in the intake manifold.
Thermotime switch installed in chain housing cover to work in conjunction with the throttle switch to operate the cold start valve.
Fuel injectors lengthened due to their elevated position in the intake runners.

Documentation of the CIS from '73 up through the '75 models is somewhat confusing, as there is just enough left out of the various books to make a hazy picture. The little factory spec book doesn't mention the specs for a vacuum controlled WUR for '74 or '75, but the factory manual does. So if one doesn't have personal knowledge of what the factory did, it's a little hard to figure out from reading the various books. Each of the books is vague in different areas, and there is not a book I have found yet that states they were definitely both used or that one was used and definitely not the other, for any of the years in question."

So it appears the 73.5 didn't have a TTS. I'm curious as to the location of the cold start valve and just it operates. I'm thinking it squirts everytime you hit the starter. If that's the case you might want to look at the wiring for the cold start valve and perhaps test the valve as well.

[Sunroof]

Ah, hence the hand throttle.............
The thermotime switch replaced the hand throttle then from the 1973.5T CIS to the 1974 CIS. But, Porsche used the thermotime switch on the 1973 MFI model prior to K-tronic CIS introduction in the 73.5T model. Does the 1973 MFI have a hand throttle? If so, it looks like someone skipped a step!

[Walter_Middie]

Sunroof,

Just so we don't get confused.....the hand throttle did not go away - I still have one on my 1975. I can't answer your question about the 1973.5, but maybe a description of my 1975 system will help you:

While the key is in the run position, power will be sent to the WUR if the Thermo-Time Switch allows it. On the left side chain cover is the Thermo-Time Switch which is the basic control for the enrichment solenoid during the starting phase. If the car is warm from running recently, or enough time has elapsed since it was started, the Thermo-Time Switch will interrupt the power going to the WUR.

The cold start valve itself has a gray and white wire and a red and black wire from the thermo-switch: Note that the gray and white wire and the yellow wire are connected to the same terminal on the thermo-switch. The WUR (warm up regulator) mounted on an intake runner base on the driver's side of the engine should have a single red wire with white stripes connected to it.

Cold start valve circuit: There should be a wire from the ignition switch to terminal 50 (this is a small blade type lug that receives a female type connector) on the starter, from terminal 50 of the starter a wire (yellow) goes to the throttle valve switch. From the other side of the throttle valve switch a wire (also yellow) goes to the thermo-switch on the driver's side chain case, this wire from the throttle switch attaches to one terminal (this is the non-ground side terminal) of the thermo-switch, a second wire is also attached to this same terminal of the thermo-switch and goes to the cold start valve. From the other side (ground side) of the thermo-switch a second wire goes to the cold start valve.

[HarryD]

The 1973.5 does NOT have a thermo time switch!