thermal time switch 69 911E specs- Help

maze · 09-25-2007, 06:48 PM

Hi Folks,
My project is a 69 911E w/MFI.
The cold start solenoid is not firing when cold, and Im not getting voltage to it. When I jump 12v to it directly it works great....gas everywhere.

I have traced the wiring back to the Thermal Time Switch on the manifold. It shows an open circuit to ground on the red/blk wire at ambient temp (70F).

This switch has a part number 901.617.117.00 and is marked -10C. That seems very cold from what I have read here on the forum for a tts.

There are two such switches adjacent on the manifold and the other switch closer to the rear of the car, is stamped 35C. The schematic shows this to be a Temperature switch (start)...not sure what it does. Its part number starts with 911.617.11X.XX (last digits are destroyed)

I have another TTS from a parts pile that has the following numbers 911.617.117.00 and is stamped +45C.

My big question is can I use the 45C part in place of the -10C part without screwing up the works?

Second question is can someone confirm the -10C part is correct for this car and why such a low temperature switch?

By the way the car is very hard to start without a gas dump down the throut (the cars...not mine!)

Thanks
Maze

jluetjen · jluetjen's Garage

What I did for cold starting my car is to run a wire from the "Start" connection on ignition switch, through the un-used fog light switch, and then back to the lower, "Start" solenoid on the MFI pump. The fog light switch is left open when starting a warm engine, and when the engine is cold, I close the fog light switch prior to starting. This sends 12V to the "start" solenoid on the MFI pump that pegs the rack at full rich.

Apparently, "back in the day" the race teams would do something similar for cold starting the MFI'd race cars, but in that case they would use a pair of pliers to manually pull the rack to full rich.

It works real well, even at temperatures below freezing. The extra "start" solenoid is a feature of the 69 MFI pumps which was dropped starting with the '70 model year. So unfortunately later model MFI cars don't have such a simple solution.

maze · 09-26-2007, 05:05 AM

Thanks for the pointer about the 69 model year.
Perhaps because there is the extra cold start solenoid on the pump, the TTS for the enrichment is set to very cold temps...
Do you happen to know what the TTS temp is for your 69 cold start valve circuit?

Thanks
Dan

jluetjen · jluetjen's Garage

Unfortunately -- no.

304065 · 09-26-2007, 06:55 AM

Yes, -10C is correct for the car. See below.

jstobo · 09-26-2007, 07:25 AM

Notice the diagram. The cold start relay should operate evertime the car is started. The time switch justs increases its activation time. Check your "black" relay in the engine compartment. It activates the cold start solenoid when the ignition is turned on. If the relay is bad the cold start solenoid will not work. If wiring is good sounds like you have a bad relay.(or none)

maze · 09-26-2007, 08:54 AM

Hi Guys,
Thanks for the great support on this.
The diagram really makes clear the funtion of the cold start valve enrichment circuit v.s. the start solenoid enrichment circuit.
It appears that the cold start valve enrichment circuit should not be functioning during a 70F day. This is where I was confused as I thought it was supposed to provide enrichment as a primary starting aid. It appears that the time switch operating the start solenoid on the MFI is the primary enrichment means for starting in warmer weather.
I will run some tests on this circuit tonight.
I did check the black relay on the cold start valve last night and it works fine. I recall there is a separate relay for the start solenoid. So hopefully that is the culprit.

Maze

Grady Clay · 09-26-2007, 08:57 AM

It is very gratifying to see questions like this answered – without me.

John, I made a slight correction to the diagram.

Best,
Grady

304065 · 09-26-2007, 09:15 AM

Quote:

Originally Posted by Grady Clay

It is very gratifying to see questions like this answered – without me.

Well, you taught us.

Early_S_Man · 09-26-2007, 11:42 AM

Both -10°C and +45°C are shown in the download [images only PDF-version of PET] parts catalog, and it is the later superceding '911' Thermo-Time Switch version shown as the secondary switch (35) in parentheses.

Seems funny to me that only the lower-rated switch is called Thermo-Time Switch in TMA, and the higher +45°C switch is just called Time Switch, while operation is identical, even if only for 2 seconds with the later-style +45°C switch!

maze · 10-04-2007, 06:17 PM

Well I cleaned up all the connections including those at the MFI cold start solenoid and added a fresh battery to the car. Starts right up every time right away! Thanks guys...