Where in the world does the ECU pull power from in stock form???

[super95awd]

Where in the hell does the ECU get power from in stock form, and what pin or pins does it go into??? I'm basically rewiring the car and somehow I got lost as to where to throw power into the ECU. I couldn't make heads or tails out of it looking at ECU pinouts. Any help would be appreciated.

 

[90blacktsiawd]

This might help
http://www.vfaq.com/mods/ecu-harness-2G.html

 

[GVR4592]

It should be coming from the mfi relay.

 

[steve]

It should be coming from the mfi relay.

Exactly.

If you understand the following you'll know how to wire up the ECU.
--------------------------------------------------------------------------------------------------------

Here's what I've posted before about diagnosing ECU powerup issues:

The 1G DSM has two main circuits for the engine. The MPI circuit and the Ignition circuit.

The ECU is connected to both but powered from the MPI circuit.

Power for the MPI circuit comes from the MPI fusable link on the positive battery terminal to pin 10 on the MPI relay and should be present all the time even with the car off. Power for the Fuel Pump and the rest of the ignition circuit comes from the Ignition fusable link on the positive battery terminal and for the fuel pump winds up on pin 3 on the MPI relay.

The MPI relay has two actual relays inside, one for the MPI power and one for the fuel pump power. The fuel pump relay has two trigger inputs, the MPI relay one. Pin 10 (black/red) in the input for the MPI power and pin 3(Black/White) is the input for the FP power. When one of the control lines to either relay is activated the relay switches the power from the input to the outpin pin(s)

The ECU receives backup power on pin 103 (red/black) from 10A fuse 19 (room) in the drivers footwell fusebox. This is used to maintain the RAM in the ECU's CPU and allow the ECU to power itself up. Like MPI relay pin 10 the backup power on ECU pin 103 should to present all the time even with the car off.

The ECU sits dormant in a powered down state waiting to see pin 110 (IG1 from ignition switch black/white) go high (to battery voltage). When pin 110 goes high the ECU pulls its pin 63 (MPI relay pin 8) low (to ground). This causes the the relay to activate and switches the MPI power from MPI pin 10 to MPI pins 4 and 5 providing power to the ECU on pins 102 and 107 along with various sensors, solenoids, injectors, ISC, and O2 Heater in the engine bay.

Shortly after battery voltage shows up on ECU pins 102 and 107 the reset circuit in the ECU wakes the ECU up and if it boots up you'll get a heartbeat on ECU pin 1, the CEL will come on for about 5 seconds, the boost gauge will display 0 (Stock ECU software on turbo cars) and the ISC on the throttle body will move in and out to rehome.

The next interesting condition is when ECU pin 108 (indirectly START from the ignition switch) goes high (to battery voltage).

The START signal also goes to the Fuel side of the MPI relay to power up the fuel pump, and to the ECU causing the ECU to do the things it needs to do the start the engine. Once the engine is running the ECU pulls it's pin 56 (MPI relay pin 8) to ground and continues to hold it low until you turn the car off or the engine stops running, to keep the fuel pump powered after you release the ignition.

The first thing you should do if your ECU doesn't power up (CEL on for about 5 seconds, the boost gauge displays 0) is check the two fusable links and the room fuse. Measure the fuses for continuity (0 ohms resistance) rather than look at them. Then check for battery voltage at the ECU and MPI relay pins. Remember that the ECU doesn't get power on pins 102 and 107 until the MPI relay is activated by turning the ignition key to RUN or START. If the MPI relay doesn't activate try grounding its pin 8 and check that power shows up on its pins 4 and 5. If that works then either the ECU isn't seeing the IG1 signal or the ECU is damaged.

If power is present on ECU pins 102 and 107, the ECU grounds are good and the ECU doesn't power up it's damaged.


Steve

 

[olmytsi]

Good info in here....subscribing

 

[steve]

While this isn't 2G specific it does cover the general technique Mitsubishi uses for powering up the ECU with a MPI relay.

If I don't fall asleep, I'll see if I can do a 2G version of this.

Steve

 

[tstkl]

wait, so If I go through my car and get rid of every wire except for those in the mpi and ignition circuit, the car will run, but nothing else will work. (aka stereo, windows, locks, all that stuff...) Is the fuel pump circuit part of the mpi circuit? That could be useful when removing unnecessary parts.

 

[steve]

wait, so If I go through my car

Can we stick to super95awd questions?

-------------------------------------------------------------------------------------------------------

Like the 1G, the 2G DSM has two main circuits for the engine. The MPI circuit and the Ignition circuit.

The ECU is connected to both but powered from the MPI circuit.

Power for the MPI circuit comes from the MPI fusable link #4 (30A) in the relay box under the hood to pin 3 and 4 on the MPI relay and should be present all the time. Power for the Fuel Pump and the rest of the ignition circuit comes from the Ignition fusable link #6 (30A) in the relay boxl and for the fuel pump winds up on pin 3 and 4 on the FP relay.

On the 2G the MPI relay and fuel pump relay are two seperate relays unlike the 1G where they are combined. The FP relay only has one trigger input and the MPI relay one. Pins 3 and 4 are the power inputs for both relays. When the control line (pin 2) to either relay is activated (pulled to ground) the relay switches the power from the input (pin 3) to the output (pin1).

The ECU receives backup power on pin 80 (red with blue stripe) from dedicated fuse 11 in the relay box under the hood. This is used to maintain the RAM in the ECU's CPU and allow the ECU to power itself up. Backup power on ECU pin 80 should to present all the time even with the car off.

The ECU sits dormant in a powered down state waiting to see pin 82 (IG1 from ignition switch) go high to battery voltage. When pin 82 goes high the ECU pulls pin 38 (MPI relay pin 2) (blue with green stripe) low (to ground). This causes the the relay to activate and switches the MPI power from MPI pin 3 to MPI pin 1 providing power to the ECU on pins 12 and 25 (red) along with various sensors, solenoids, injectors, ISC, and O2 Heaters in the engine bay.

Shortly after battery voltage shows up on ECU pins 12 and 25 the reset circuit in the ECU wakes the ECU up and if it boots the CEL will come on for about 5 seconds, the boost gauge will display 0 (Stock ECU software on turbo cars) and the ISC on the throttle body will move in and out to rehome.

The next interesting condition is when ECU pin 71 (yellow) (indirectly START from the ignition switch) goes high (to battery voltage).


I hope I got this right.

Steve

 

[super95awd]

Wow, so more or less, taking into consideration that my MPI relay is gone, all I need to do is wire switched 12v power to pins 12 and 25, constant 12v to pin 80, and pin 71 to the starter lead so it sees 12v when it's starting? Thanks for the information BTW, that took a little bit of figuring out

 

[steve]

You should feed 82 the switched 12v also.

Steve

 

[super95awd]

But doesn't pin 82 seeing power just ground pin 38 to provide power to the MPI relay? Doesn't seem like it provides any important ECU powering function, but I've been wrong before.

 

[steve]

On a 1G the ECU gets a shutdown signal when the ignition switch is turn off. Then 5 seconds later it floats the MPI control line to turn the relay off. I forget offhand what it does in the code but I suspect the kills the engine, turns off the fuel pump, and resets the ISC. It may do other houskeeping work before the power turns off. I expect a 2G does this as well and it has more control over the power than the 1G ECU does.

Steve

 

[super95awd]

I was just saying since I have no MPI relay, it can't really perform any of those functions. I guess I'll just try it without powering Pin 82 and see what it does.

 

[steve]

Whatever, you can try it both ways and see what works for you.

Don't forget to fuse things.

Steve

 

[super95awd]

Yep, got that covered. I still need to figure out what size fuses were used stock for everything, but I'm getting there. Thanks for all your help man.