CSV Temp on 73 MFI

vol96 · 10-10-2004, 07:56 AM

At what temp should the cold start valve be activated on a stock 73 with MFI?

Thanks,
Joe

Grady Clay · 10-10-2004, 08:54 AM

Joe,

I did a cursory look through my limited stuff and couldn’t find the numbers.

An easy test is to remove the thermo-time switch from the breather plate and connect an ohmmeter across the switched contacts. Put it in a pan of ice cold water on the stove with a thermometer. Slowly warm while stirring vigorously. Note the temperature where the contacts open. You can repeat several times to get better precision.

The next test is to connect an ohmmeter across the contacts and apply 12 V to the heating element contacts. Confirm the switch opens within a few seconds, the colder temperature the longer time.

Between tests you should put the thermo-time switch in your freezer for a few minutes.

I have never seen one of these change calibration, just fail. The failure modes that I have seen are; heater circuit open, switch contacts stuck closed, switch circuit permanently open, and internal parts come loose (rattles.)

You should confirm the thermo-time switch is wired correctly and it gets 12V to the heater when cranking.

Best,
Grady

vol96 · 12:43 PM

Grady,
Thanks for the reply and the suggestions.

Unfortunately you lost me at 'breather plate'. Do 72-73 MFI engines have one of those?

My car has a CSV on top of the fuel filter. Maybe its called a cold start solenoid. I works when 12v jumped to it.

Thanks,
Joe

Early_S_Man · 01:28 PM

Joe,

The CSV is on the fuel filter console, but it is controlled by the Thermo-Time Switch mounted [screwed into] on the oval breather plate on the top of the engine centerline ... oil return from the FI pump, and breather tube to the oil tank are also connected there.

The Cold Start circuit has three components in the diagram below:

1. #14 -- Thermo-Time Switch -- 'G' terminal is heater element of approx. 15 - 25 Ohms, which is powered by starter solenoid terminal #50 ... 'W' terminal is switched ground controlled by bi-metallic thermostat element ... closed at temperatures below approx 112°F, open above 112°F.

2. #52 -- Auxilliary Start Relay [round black multipurpose relay] located on electrical panel on left side of engine compartment

3. #12 -- Cold Start Valve ... recieves power from Aux. Start Relay

The Thermo-Time Switch should be stamped with opening temp in Celcius on the lower brass tubular part that is exposed down below the breather ... I believe it is around 112°F.

There are two contacts on the Thermo-Time Switch marked 'G' and 'W' ... which are different sizes to prevent a wrong connection!!!

vol96 · 10-10-2004, 07:10 PM

Well, looks like I need a TTS (thermo time switch).

Removed from case breather and put in freezer for 15 min. Still registered 0 ohms on ohmmeter. So its always open, not completing circuit to the cold start valve.

BTW, its stamped as 45deg C, part number 91161711700

Grady - Thanks for the help
Joe

vol96 · 10-10-2004, 07:12 PM

Grady Clay · 10-11-2004, 07:14 AM

Joe,

Here is an internal diagram of the thermo-time switch.
I don’t remember which terminal is which.
Remember, the housing is an electrical connection.
In the Factory diagram Warren posted above, #14
is understandable only if you already know what is inside.

If you are reading zero ohms across the switch contacts then they are closed.
That is correct for temperatures below 45C.
At higher temperatures, the switch is open and the
ohmmeter should read infinite resistance.
I will guess the heater would measure 10-30 ohms.

Best,
Grady