[MTP78Z]

Could someone explain the theory of how the Thermotime Switch and Cold Start Valve work more thoroughly than my Factory Service Manual does?

I'm a little confused about two things:
1) when does the CSV actually shoot gas out, and
2) what's the impact of a dead thermotime switch besides being harder to start.

My 78 FSM says fuel is injected when the water temp is below 57 to 72 degrees Farhenheit which would lead me to believe that nine months out of the year here in Southern California my CSV is probably never used anyway. Is that true or does it really shoot out gas no matter what the temp is on the first crank?

What is the effect of a dead thermotime switch or a bad connector to it? Besides being harder to start is the current running through the thermotime switch needed for anything else that would impact the way the engine runs?

Thanks,
Mark

 

[zcarcreationscom]

1) The CSV shoots gas out only when the car is cold and then for a maximum of 12 seconds. The actual length of duration, from 0-12 seconds, is directly affected by the temperature of the engine coolant as measured by the thermotime switch. Also, the air regulator works with the CSV as an electronic choke. However, the air regulator is not controlled by the thermotime switch or the ECU. It operates as a stand-alone unit.

2) A dead thermotime will do nothing to the car except render the CSV ineffective. The thermotime switch does nothing else.

I live in Alabama and removed both the CSV and air regulator. The car starts just fine for me but results may vary.

Craig Borden
www.zcarcreations.com

 

[johnh240]

A primer on thermotime (get it? primer? yuk-yuk. Thermo-Time = temperature and time. First, the cold start valve gets it's voltage from the same circuit as the starter signal so that the voltage is ONLY present when you turn the key to 'start'. That voltage goes through the thermotime switch. Now the switch will only be closed IF the engine temp is less than that 57 to 72 degrees that you referenced (thermo) and only will operate for a few seconds at most (time). Inside the thermotime switch is a bimetal switching device that reacts to temperature. The current from the starter circuit is routed through the bimetal switch (if it is cold enough to be closed) and then to the cold start valve (or injector). As the current flows through the bimetal switch it heats the bimetal up causing it to eventually bend enough to open the circuit and shut off the cold start valve. This is done so that if it is really cold out and the engine is going to take a while to get up to temp and it is not starting, the csv won't continue to pump in fuel and flood the engine during excessive cranking times. The cold start valve is under pressure (or should be under some pressure if the fuel pump check valve is working) so as soon as it sees some voltage applied, it opens and releases fuel. The pressure should remain up since during cranking the fuel pump also begins to receive voltage to start pumping. As soon as the key returns to the 'on' position, voltage to the CSV stops and the CSV should stop injecting any extra fuel (unless of course it is sticking and decides to leak a little extra in after you are started). Disabling the thermotime and csv in a warm climate will just cause hard starting during cooler conditions. It has no effect on any other circuits in the efi. It is a standalone system.

 

[MTP78Z]

I think I can rule the CSV out

Thanks for the explanations. My car is suddenly very hard to start and I personally don't think the CSV is the problem as I doubt it was very necessary in the first place since I live in Los Angeles.

Plus since white smoke comes back through the air cleaner when I crank it makes me think that something else is wrong.