What is "needed"? Only the EMS box it's self. What is needed to make big power? Lots of stuff. At minimum you would want to convert to Manifold Absolute Pressure for load measurement. While the EMS will use and read the stock 1G MAS or even a 2G MAS very nicely, MAP is much less restrictive. You are getting rid of the stock restrictive MAS and instead connecting a pressure sensor to the intake manifold. The cheap way out is to use the GM 3.0 bar MAP sensor. The sensor price is about $55. while cheap and fairly consistent, it is difficult to set up to accurately read correct boost pressure. The AEM sensors are a bit more expensive but are much more accurate and you can more easily trade calibrations with others.
You will remove the stock MAS and make your own turbo inlet pipe. Usually just a 2.5" or 3" pipe with a filter on the end. A slight "S" bend or possibly just a 45 degree bend can usually do the trick. We don't have a ready to go kit for this, but if you are to this point already making up an intake pipe shouldn't be too much of a stretch for you.
Since the stock Intake Air Temperature sensor is located inside the stock MAS, you need to add one to the intake piping. You want to mount it after the intercooler, but away from the motor so it does not heat soak as much. We have weld in steel, stainless steel and aluminum bungs for this purpose. The GM AIT sensor works nicely for the price ($25) and it uses a standard 3/8" NPT thread.
To tune properly for fuel, you will really need to buy or borrow a wide band air fuel ratio meter. Prices are dropping now on these to such an affordable range that you really should just buy one. The AEM one is excellent, there are also other low price options.
Other more luxury options would be the AEM EGT sensor. Since EGT is most useful to see retarded timing caused by knock, this isn't as necessary with the EMS. You can see and log raw knock, knock and timing retard from knock all on the EMS. But also monitoring EGT gives you a little more information to what is going on in the motor.
5V Power- Get this from the MAS connector. You want the Green/Red wire located at pin number 4
Sensor Ground- Get this also from the MAS connector. You want the Green/Black wire at pin number 6. When connecting to it, make it a double splice. You will also need sensor ground for the AIT sensor.
MAP Signal- The EMS for the 1G Eclipse it set up to use the stock ignition check connector wire for the MAP signal input. This is on the firewall, next to the windshield wiper motor. It is in an oval connector sized for two pins, but there is only one pin in the connector, it has a Yellow/Red wire.
The AIT needs to be installed n the intercooler piping, after the intercooler. Somewhere in the upper intercooler piping is fine. We stock weld in bungs in both steel and aluminum. The thread on the GM style AIT sensors is 3/8" NPT.
There are two wires on the AIT, polarity does not matter. One is the signal wire to the ECU. Connect it to the Green/Orange wire at the MAS connector pin number 8.
The second connector is to be connected to sensor ground at the MAS connector. You want the same Green/Black wire at pin number 6 that you used for the MAP sensor.
The 1G knock sensor is a miserable sensor. You really need to switch to the 2G sensor. The part number is MD300670. The wiring connector and threads are the same, it is a direct bolt in. The 2G sensor is much more communicative and linear.
Take it out while you are getting familiar with the EMS and doing your initial tuning. You will be running rich at the start while you are goofing around with things. The cat will die pretty quick trying to burn off all that extra fuel.
Disconnect it. If you have any trouble getting the car started up, you will be spending too much time standing on your big clutch and putting a lot of unnecessary pressure on an under lubed crankshaft thrust bearing.
If you find your self constantly cranking on the motor and you are not getting it to fire up, you could possibly be flooding the motor with fuel. The quickest way on a 1G to turn off the injectors is to disconnect the injector resistor pack wiring connector. Then if you need to spend some time cranking on the motor to check for spark or other problems, you wont be digging your self deeper into a hole. Check the spark plugs for excess fuel.