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Ok guys, Here's my first ever tech write up.
I just figured this out last night so be kind if this has already been covered.

I've been having a lot of trouble starting my mk2 lately. As the weather got colder the worse the problem got. Having checked the TSRM, I figured out that the cold start injector was not firing. Ok, so same problem umpteen million other supra owners have had to deal with. However, being low on cash right now, I couldn't just run out to Toyota and buy a new one, and it's too cold to go roaming through the junk yards. So I started looking through the electrical diagrams, trying to figure out another way. Here's my solution.

Now in case you didn't know, the cold start injector is not powered by the ECU. It's actually powered by the starter circuit. When the starter is not cranking the injector does not fire, period. The ECU only decides when to allow the injector to fire, based on coolant temperature. It fires the injector by letting it go to ground. The injectors positive side is always connected so any time the starter cranks the injector has power. The "Switch" is after the injector on the ground side. So we don't actually need it.

By connecting the injector directly to ground it will always fire any time the starter runs. Ok, it's true that once the engine is already warm this will make it go rich when starting, but only for an instant. As soon as the engine kicks and you let off the key, it's back to running on the primary injectors only. Not a real problem. And it seems to work like a dream on my car. Instant starting again, nice.

So, here's the mod. It's easy and only cost about 50 cents.
Disconnect the start injector time switch. When looking into the connector, (that is, the side with the wires), the pin you want is on the right side of the connector when the dimple inside the connector is facing up. You'll see what I mean if you look inside it. You need to run a wire from this pin to ground.

To protect the circuit use a 50k ohm resister in line with this wire to limit the power going though it. That's it.

The quick and easy way to do this is run a wire to the negative terminal on the battery or any convenient bolt on the block or chassis. As long as it's grounded. Cut the wire in half and use the resistor to splice the wires back together. Wire/Resistor/Wire. Connect one end to the battery and the other to the pin of the connector. Use some electrical tape to hold everything together and make sure nothing can get caught in the belt and such. Use your imagination. Instant temporary repair until you can get a new switch.

By the way, although this mod is currently working in my own car...
Use at your own risk. If anything goes wrong, don't blame me. ;)

Peace.
 

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Hmmm? Okay so the computer only sends positve to the switch when the starter is cranking? Or by grounding it out manually the injector is constantly open when the engine is running? If the latter be true, you may want to add a switch inside to enable a shut off of this circuit.......Just a thought./

JoelD
 

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No, the starter sends positive to the injector any time the car is cranking. the time switch connects the injector to negative when the engine is cold, completing the circuit, and firing the injector. By connecting the time switch connector directly to ground the injector will fire any time the starter runs, but only when the starter runs. Still working on a better solution though, and keep in mind it is only supposed to be a temp fix. Also, the 50K ohm resistor may be too big. Working on finding the perfect value, so will get back with that later.

To be continued...
 

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hey does anyone know how to "DIY" the cold start injector time switch for another reason bcuz my MKII's time switch is broken, supposed to read 3-5ohms but shows 31ohms, what should i do, im too broke to replace it in an instant, i want to do somethin wit it, does anyone know what i should do, cuz when da car is on running temp, the car always idles high due to the cold start injector on all the time....
 

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So, here's the mod. It's easy and only cost about 50 cents.
Disconnect the start injector time switch. When looking into the connector, (that is, the side with the wires), the pin you want is on the right side of the connector when the dimple inside the connector is facing up. You'll see what I mean if you look inside it. You need to run a wire from this pin to ground.

To protect the circuit use a 50k ohm resister in line with this wire to limit the power going though it. That's it.
Not wanting to sound like a noob, but where is the start injector time switch?
 

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RR, it's one of the two sensors on top of the thermostat housing to narrow it down for you.

Thanks for the info, as I can use it to fix it in a different way! The usual problem many have is on hot starts, the cold start injector is fired, causing the engine to run rich for 10 seconds. I just want to disable the injector when the engine is warm. Should be able to figure it out now! Thanks again!
 

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Someone was looking for this recently so I thought I'd bring it up again.

I borrowed the following writeup from Supramania - it was written for the MarkIII but I just looked through the '86 MarkII TSRM and verified that the wiring described below for the MkIII is the same for our MkIIs.

Cold Start Injector and Thermal Time Switch


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.
 
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This reminds me of a thread I saw a couple years ago that I have been trying to find. I have a problem in the warm weather when I re-start the car after it has been driven and is still hot. When I re-start the car, it runs rough and wants to stall unless I give it some gas. As soon as I am moving again, it runs normally. Could this be CSI related or any other explanation would be appreciated.
 

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Sounds like EGR runon (stuck open) ??

This reminds me of a thread I saw a couple years ago that I have been trying to find. I have a problem in the warm weather when I re-start the car after it has been driven and is still hot. When I re-start the car, it runs rough and wants to stall unless I give it some gas. As soon as I am moving again, it runs normally. Could this be CSI related or any other explanation would be appreciated.
 

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I'm not a big fan of fixing a problem by bypassing something.
temporary bypass for shooting trouble. If it starts better then replace.
 

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It's highly unlikely that anything to do with the CSI is causing your hot start issue. It's much more likely that heat soak in the AFM is the cause. That's why the engine smooths out after about 10 seconds of either running or driving. The cooler air going through the AFM gets it back in the temperature range where it operates properly. I've heard that some people have wrapped insulation around the AFM to help with this.
Extreme AFM heat soak can actually prevent starting at all until it cools down.
 
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