Hi atl93FD,
Another rotorhead here.
You are right in that the FD RX7 injectors are high impedence. I assume you've got another pair of secondary injectors in the primary position which is a fairly common mod.
The stock FD air temp sensor is pretty useless. I'm not sure if it's the age or the design, but they don't seem to move much. I install Haltech E6K's on FD's and the difference in response is huge. As soon as you come on boost the air temp goes up (that is until the water injection kicks in). The design of the sensor is different with the stock one being a solid core whereas the Haltech ones have the thermocouple "open" inside a protector with holes in it. I think this might help.
In saying that it sounds like your water consumption might be a bit low though. Usually on a stock FD you can't even touch the intake manifold it's so hot (after some "enthusiastic" driving). After installing water injection they run as cold as....well...something that's real cold. Nothing like seing a turbo/manifold glowing so hot that you can just about see through it and the intake is still cool to touch!! If your intake is still hot then you need more water.
Intake temperature is a handy way to tune the water injection. The idea (in my opinion) is to try and keep the temperature as smooth as possible. Not too hot, not too cold (too cold a mixture can have adverse affects on fuel mixing properly). This makes the car easier to tune as it's not jumping around the compensation maps so much, and makes the HP and A/F ratios very consistent.
Hope this helps
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