Fuel Mods

Pin	1990-94 Turbo	Wire Color	Mod	Results
4	Oxygen Sensor	wht	Tap into the line with voltmeter	Monitor O2 Readings
8	Intake air temperature sensor	grn-org	Install 10k potentiometer	Add resistance to richen full throttle A/F ratio
16	Barometric pressure sensor	grn-yel	Install 10k potentiometer	Add resistance to lean full throttle A/F ratio
105	Waste gate solenoid valve	org	Tap into line with LED	Monitor when ECU sees excess knock and tries to reduce boost

You can either use the check connector (click here) or tap into the ecu wire #4. Either way will give you the same results.

Solder up some wire leads to a 10k potentiometer using the last 2 terminals so that when the dial is turned as far as it can go counterclockwise you have 0 ohms resistance. Cut wire 8 and solder the potentiometer in series. It doesn't matter which side of the potentiometer goes to which wire. You should start tuning the car with the knob turned fully counterclockwise (the ecu will see the real air temperature). By turning the knob clockwise the ecu will think that the air is cooler and will add fuel to accommodate the denser air. Do not try and tune without monitoring the O2 sensor with a voltmeter. Tune until you get .88-.92 at wide open throttle. You will only be able to adjust full throttle A/F ratio with this mod. It won't do anything for the lower rpms. Don't adjust this unless you've done some mods to require more fuel. (Mass air flow sensor hacking......etc) If you're running lean without having done mods then check the intake piping between the turbo and mass air flow sensor.

Solder up some wire leads to a 10k potentiometer using the first 2 terminals so that when the dial is turned as far as it can go clockwise you have 0 ohms resistance. Cut wire 16 and solder the potentiometer in series. It doesn't matter which side of the potentiometer goes to which wire. You should start tuning the car with the knob turned fully clockwise (the ecu will see the real elevation). By turning the knob counterclockwise the ecu will think that the car is at a higher elevation and will reduce fuel to accommodate less oxygen. Do not try and tune without monitoring the O2 sensor with a voltmeter. Tune until you get .88-.92 at wide open throttle. You will only be able to adjust full throttle A/F ratio with this mod. It won't do anything for the lower rpms. All cars can benefit from this since Mitsubishi programmed the ecu so that it runs rich at full throttle. Don't try and do this unless you understand the fuel system in the car. If you lean it out too much you can cause detonation that can destroy your engine.

Tap off of wire 105 (orange) with either a 12volt internal resistor LED (available at some Radio Shacks) or use a regular LED with a 470 ohm resistor in series (Do not use regular indicator light bulbs). You must have either the boost control solenoid installed even if you're not using it or solder a 40 ohm resistor in it's place. Whatever you do don't just short the 2 wires together or you can damage the ECU. The LED will not work without either the resistor or boost control solenoid installed.

When car is turned on the LED will be ignited for 3-5 seconds. It will flash on and off about 10 times then should remain off. This is completely normal and it's the ecu that is playing with the boost control solenoid.

If the ecu detects excess knock and it wasn't able to reduce it by slightly pulling the ignition timing back a few degrees then the LED will start to flash. This is the ECU closing and opening the boost control solenoid to gently reduce the boost level. If knock is still present the LED will remain lit solid and timing will be pulled further back. If you see this happening it is wise to back off the throttle.

If the LED remains lit solid at all times the ECU thinks that you're using cheap gas. The timing has been pulled back and the ecu is trying to limit boost to 8psi by closing the boost control solenoid. The ecu will eventually reset itself but it's much faster just to reset it. You can reset the ecu by pulling the bottom right hand fuse for 10 seconds (after the ecu has clicked off). If it happens again and you're using premium gas then start looking for problems. Check ignition timing, fuel pressure, a/f mixture, wastegate actuator, knock sensor and vacuum leaks. This is even more important if the boost control solenoid isn't hooked up to the wastegate actuator (you have some other form of boost control) and the ecu no longer controls boost.