Should the cold start injector have voltage going to after the engine is warmed up? I thought that it was only supposed to fire when temps were below ~32 degrees. I haven't pulled the injector out to see if it's actually spraying fuel, but I'm pretty sure it is given the change in how the engine runs at idle when I unplug it, even after the engine is warm.

It has 12V all the time. The thermoswitch at the side of the plenum grounds the circuit.

Are you sure?

My understanding form a post from McMark a while back here is that the cold start injector power wire is connected to the starter wire. Which means that it should only fire when the engine is cranking, not when the engine is running. So disconnecting the injector while the car is running shouldn't have any effect, regardless of if the thermoswitch is operating properly.
However, If I disconnect the cold start injector when the engine is warmed up, the idle starts to wildly fluctuate.

Yes, I'm sure I was wrong earlier.

I rechecked my wiring diagrams and that's correct: at least on the D-Jet, the 12V comes from the starter circuit; specifically the 4-pin D-Jet connector on the relay plate, wire #4.

However, the thermoswitch closes the circuit to ground below around 32F/0C, so if the temps are above that the valve doesn't fire.

So you've got two weird things going on: power when the starter is not engaged, and apparently a ground somewhere in the thermoswitch side.

Trace the power side of the connector to see if it's going to pin #4 (specifically "IV") on the white 4-pin connector on the relay plate. The wires are all white so you'll have to disconnect both sides and use an ohmeter. For reference, the pins are as follows:

I - powered from the power relay, should be hot with the key on
II - powered from T14-1 start power, signal to computer of the starter being engaged
III - ground side for fuel pump relay, controlled by computer
IV - Power from T14-1 starter circuit to power the CSV

Then go to the ground side of the CSV connector and disconnect the thermoswitch; I'd not be surprised if it was still grounded, indicating a wiring short between the CSV and the thermoswitch. If not, then you can ohmeter the switch at room temperature to see if the circuit is closed (it should be open); then let it cold-soak in your home freezer and see if the circuit is open (should be closed).

Finally, if you're at ambient or above and the CSV is working and you disconnect the CSV plug and the car runs poorly...that tells me the engine is running lean and the CSV is making up the slack. So you might actually have three issues...get the car running without the CSV connected, because that's the way it's supposed to be above freezing temps.

Apologies for the red herring.

@GregAmy

Thank you, this is super helpful. I'm trying to trace down a very intermittent issue where the car will all of a sudden run super rich, the idle will fluctuate and wants to stall. When going over all of the FI components again I ran into this weird CSV issue. Unfortunately simply disconnecting the cold start injector didn't fix the issue like I had hoped although it did effect the idle, which is what led me to thinking it was firing when it shouldn't be.

Not only does the Djet CSV have full time power to it, it also has full time pressurized fuel to it.

It can cause a rich mixture just by leaking which they are know to do. You cans send the valve out for cleaning and pressure testing to verify or just completely remove it from the engine fuel and FI harness.

Wait, I thought we just established that it is only supposed to get power when cranking?

Good call out about it possibly leaking. I didn't even consider that. I am fairly certain that it's firing all the time when plugged in because even when the engine is warm unplugging it alters the way the engine runs (runs more lean when disconnected).

Since I don't need it, maybe I'll try removing the injector and plugging the hole on the plenum somehow blocking the fuel line that goes to the injector. Trying not to get too excited yet, but maybe this is the source the car's intermittent issues. If it's leaking, it's likely that it could be doing so inconsistently which would certainly explain the erratic lean/rich behavior.

Oh...yeah yeah yeah,...that's what I meant to say...only while cranking.

Still can leak if it has pressurized fuel behind it, which is all the time the fuel pump is working.

Crap. It's been a long day- I realize all this time I was talking about the Air Temp sensor that plugs into the top of the plenum.

Of course doesn't change the fact that my cold start valve could be leaking and be the source of the intermittent issues. I will look into that.


So now that I've got my head on straight, can someone school me on how the air temp sensor (TS1) works? You may be impressed to learn that I've adjust my engine to both run with it and without it at various times.

It's just a thermistor that inputs into the computer which does some non-solid-state analog magic calculation to change...something.

Anders says "Expected value...300 ohms @ 68 deg. F"

"Failure Modes
Open: Makes the mixture somewhat richer. Check with an ohmmeter.
Shorted: Makes the mixture somewhat leaner. Check with an ohmmeter. "

https://members.rennlist.com/pbanders/DJetParts.htm

Ok, well that tracks. Wish I could start this thread over.
That said, I at least have something else to test- the cold start valve for leaks.