The cold start injector (CSI) on your car injects fuel into the intake manifold to help with cold starts (duh). The thing to keep in mind (for the moment) is it operates *only* under the following conditions:
1) When the coolant temperature is below appx 100 F.
2) When the engine is being cranked.
Now having said that there's more to the story. The CSI gets power from the same place as the starter. That's the reason it works only while the engine is being cranked. It gets a ground from the Thermal Time Switch (TTS). This device is mounted on the top of your thermostat housing and does two things:
1) Only allows CSI operation when coolant temp is below appx 100 F.
2) Only allows CSI operation for a max of about 8-10 seconds even if the engine is cranked longer. This is to prevent the engine from being flooded.
The way it does this is the TTS also receives power from the starter. It uses this power to run a little heater inside it. This heater is coiled around a bimetal contact, the same contact that supplies ground to the CSI. For those not familiar with bimetal it's simply two different metals joined together with each having different coefficients of expansion. Invented by John Harrison, a gifted Englishman who solved the greatest scientific problem of his time, bimetal when heated will warp because one metal expands faster than the other. In the TTS this strip moves away from a fixed contact and breaks the ground circuit:
http://tinyurl.com/6d2r23
From this we can see the bimetal strip is influenced by both coolant temperature *and* the (starter circuit powered) heater coil wound around the strip. Therefore two conditions can exist:
1) Coolant temp above appx 100 F (hot engine): Bimetal ground contact is open...no CSI operation will occur.
2) Coolant temp below appx 100 F: Bimetal ground contact is closed...CSI operation will occur when the starter is cranked but as the heater warms the contact strip the contacts will open in appx 8-10 seconds. It should be clear that the warmer the coolant is at any given start the more temperature "bias" will already be on the bimetal contact and the less time it wll take the heater to open it and kill the CSI. Again, if the coolant is already above appx 100 F it won't operate at all.
So the CSI can be controlled by the TTS using both temperature *and* time. Must be why it's called a "Thermal Time Switch" eh? (Toyota calls it a "Start Injector Time Switch" but everyone else calls it a TTS. They've been used to control CSIs for over 25 years).
Lastly, a little extra to confuse you: The ECU can also control the CSI using the STJ pin on the ECU. STJ supplies an alternate ground for a maximum of 3 seconds longer to the CSI whenever the coolant temp is between 20 and 40 C. It uses the EFI coolant sensor to do this, not the TTS, and is in addition to, and completely separate from, the TTS function. The engine must still be cranking for this to happen though.
Two things to keep in mind:
1) The CSI needs periodic cleaning. Not difficult but needs to be done right.
2) If you crank a cold engine for more than 8-10 seconds you should wait a minute for the bimetal strip in the TTS to cool and again provide ground to the CSI. In other words cranking again too soon will get you nothing because the TTS has already cut the CSI off. The ECU may take over but the temp has to be in the range stated above. Don't waste your battery.
Cold Start Injector and Thermal Time Switch
Linear Mode
