I swung by ECM tuned and met the legend himself! First of all, what a nice guy. Second, he said my ECU has nothing wrong with it so it's probably something in the harness. The clicking that he hears he suspects is the MPI relay, but he said that last plug that's not plugged in is the plug that powers the ECU. So the fact that the ECU is trying to trigger the MFI relay means that there's a wire that's powering the ECU when it shouldn't be.

Just found that connector B56 is causing the issue and tested voltage on each pin. Here is the list of reading and what each pin is labeled as.

Pin 81 - sensor impressed voltage - 4.5v
Pin 80 - backup power supply - 12v
Pin 76 - front O2 - 4.5v (also has my afr gauge spliced in)
Pin 73 - MDP - 4.5v (also has my boost gauge and sensor spliced in)
Pin 72 - IAT - .62v
Pin 92 - sensor ground - .6v
Pin 90 - MAF - .2v
Pin 87 - closed throttle position switch (idle switch) - .6v
Pin 86 - vehicle speed sensor - 9v
Pin 85 - barometric pressure sensor - .25v
Pin 84 - TPS - 1.08v
Pin 83 - coolant temp sensor - .6v
Pin 82 - ignotion switch - 12v

I am now definitely thinking that when I accidentally tried to jump my fuel pump and accidentally hooked to the engine speed reference plug on the harness that it melted some wires somewhere

tschuhly said:

I swung by ECM tuned and met the legend himself! First of all, what a nice guy. Second, he said my ECU has nothing wrong with it so it's probably something in the harness. The clicking that he hears he suspects is the MPI relay, but he said that last plug that's not plugged in is the plug that powers the ECU. So the fact that the ECU is trying to trigger the MFI relay means that there's a wire that's powering the ECU when it shouldn't be.

Just found that connector B56 is causing the issue and tested voltage on each pin. Here is the list of reading and what each pin is labeled as.

Pin 81 - sensor impressed voltage - 4.5v
Pin 80 - backup power supply - 12v
Pin 76 - front O2 - 4.5v (also has my afr gauge spliced in)
Pin 73 - MDP - 4.5v (also has my boost gauge and sensor spliced in)
Pin 72 - IAT - .62v
Pin 92 - sensor ground - .6v
Pin 90 - MAF - .2v
Pin 87 - closed throttle position switch (idle switch) - .6v
Pin 86 - vehicle speed sensor - 9v
Pin 85 - barometric pressure sensor - .25v
Pin 84 - TPS - 1.08v
Pin 83 - coolant temp sensor - .6v
Pin 82 - ignotion switch - 12v

I am now definitely thinking that when I accidentally tried to jump my fuel pump and accidentally hooked to the engine speed reference plug on the harness that it melted some wires somewhere

Click to expand...

I assume you met Tom at ECMTuning, I'm glad he also thinks this isn't an ECU hardware issue.
The MPI relay or relays since you have a 97 GST should click when you turn the ignition to the RUN position and the when the ECU sees the engine turning over, then again about 5 seconds or so after the engine stops turning and the same delay after you turn the ignition off. What it shouldn't do is chatter, switching on and off like a pissed off squirel.

Once again I'm not sure what or how you were testing by pulling a connector off and on. It's generally a bad idea to do so while the ignition switch is on.

A couple things:
I assume you no longer has a front O2 sensor and only the Wideband is connected to pin 76.
If you have two things attached to the MDP you need to disconnect the boost gauge on only connect the MAP sensor.
How are you measuring the voltage at the sensor ground, actually what are you using for the negative (ground) voltage reference for all these measurements. Each should be measured from the ECU ground point.
Mitsubishi MAFs output a frequency alternating between roughly 0 and 5v. So a voltage measurement doesn't tell much.
The VSS is much the same in that its a series of pulses as the transmission turns and it varies from 0 and battery voltage.
TPS voltage on a 2G has a wide spec for the output voltage 400 to 1000mV depending on where the internal IPS switches. Your is a hair outside spec at 1080mV that could be due to adjustment of the TPS or measurement offset due to your choice of negative point.

Hey Steve,

- I do have my wideband/narrowband sim hooked to my front O2 sensor plug.
-so I would want to unplug my MDP and only use my 3.5bar and that is okay even though I'm not set up for SD?
-i tested the relays with OEM reading and also connecting pins to 12v to hear for a single click.
-i was using chassis ground, so that was something I did wrong.

I tried to go through diagnostics using AI and AI concluded that it is internal to my ECU so now I'm confused. I will post the AI summary here to see if you all agree with its conclusion and hopefully clear up my confusion .

"Here is a complete, scannable summary of the diagnostic testing and results you can send directly to an ECU repair specialist or a peer for review.

Diagnostic Summary: 2G DSM Main Fuse Short Circuit​

The Vehicle: 2G DSM (1995–1999 Mitsubishi Eclipse / Eagle Talon)
The Initial Symptom: 20A Engine / MFI Fuse blows instantly when the ignition key is turned to the ON position.

---

Initial Pin-Voltages (Key ON)​

Initial multi-meter testing on ECU Connector B-56 yielded abnormal reference voltages due to an ongoing circuit failure:

• Pin 82 (Ignition Switch Input): 12V (Normal)
• Pin 80 (Backup Power Supply): 12V (Normal)
• Pin 81 (5V Sensor Impressed Voltage): 4.5V (Faulty – Dropped to 0.01V once aftermarket gauges were unplugged, proving the ECU 5V regulator loop was dead and backfeeding voltage).
• Pin 73 (MDP Sensor Input): 4.5V (Faulty – Backfeeding due to an aftermarket boost gauge splice).
• Pin 92 (Sensor Ground): 0.6V (Faulty floating ground voltage offset).

---

Step-by-Step Isolation Process​

1. Isolated Engine Bay Test (Harness Verification)​

• Action: Completely disconnected the ECU logic board from all vehicle plugs. Reconnected all factory engine bay components (Crank, Cam, MAF, Injector Resistor Pack, Coil, TPS, and O2 sensors). Kept the short-prone ISC motor and aftermarket gauge splices disconnected.
• Result: The 20A Engine fuse did NOT blow.
• Conclusion: The vehicle's factory wiring harness, sensors, and engine bay components are completely healthy and free of shorts-to-ground.

2. ECU Plug Isolation Test​

• Action: Turned the key OFF, plugged ONLY Connector B-56 (low-voltage sensor side) back into the ECU, and turned the key ON.
• Result: The fuse did NOT blow.
• Conclusion: The internal 5V regulated sensor loop, logic chips, and microprocessors on the B-56 side of the ECU board are structurally healthy and not grounded.

3. Pinpointing the Short​

• Action: Attempted to plug in the remaining power distribution connectors. Left Connector B-53 completely unplugged, but plugged Connector B-54 into the ECU.
• Result: The 20A Engine fuse blew IMMEDIATELY upon key ON.
• Conclusion: The short circuit lives exclusively inside the ECU casing on the B-54 circuit paths.

---

Final Diagnostic Verdict​

The vehicle wiring harness is safe. The issue is a hard internal short-to-ground inside the ECU on the B-54 power rail.
Because B-54 handles heavy-duty 12V power distribution, the internal failure is localized to one of two main circuits inside the computer:

1. The MFI Relay Ground Driver Circuit (Pin 38): A transistor or diode controlling the main vehicle power relay has internally melted down to the ECU's ground plane.
2. The Oxygen Sensor Heater Drivers (Pins 57 & 58): A solid-state grounding transistor used to power the high-amperage O2 heaters has internally failed and welded itself directly to ground.

Next Action Item​

The ECU board requires physical inspection by a specialist to replace fried driver chips (such as the M5269L series or solid-state transistors) and repair vaporized copper traces leading from the B-54 pin header.
If you want, tell me:

• What brand/model of aftermarket gauges you are using
• Where they are getting their 12V power from

I can help verify if your gauge wiring is safe before you plug in a repaired ECU."

tschuhly said:

Hey Steve,
- I do have my wideband/narrowband sim hooked to my front O2 sensor plug.
- So I would want to unplug my MDP and only use my 3.5bar and that is okay even though I'm not set up for SD?
- I tested the relays with OEM reading and also connecting pins to 12v to hear for a single click.
- I was using chassis ground, so that was something I did wrong.

Click to expand...

One or the other, not both. You don't have to be running Speed Density to connect a MAP sensor and log it. We did that long before DSMLink supported SD.

So they test good are they working correctly in the car?

If you use anything other than the same ground point the ECU is using you can create offset voltages due to the resistance between the two points. Best one is right at the ECU connector, second best is where the ECU ground connects to the chassis.

Good luck with the AI results. I'm not here to compete with or explain when it spits out garbage. That's a waste of my time.

steve said:

Good luck with the AI results. I'm not here to compete with or explain when it spits out garbage. That's a waste of my time.

Click to expand...

Woah, I'm not trying to argue or say your wrong. I literally was just trying to use it to make sure I was doing something that I have never done correctly and figured I'd try AI. If what it's saying is incorrect, then all I'm asking is to let me know.

I'm still planning on testing what you said tomorrow when I get a chance.

Here are some pictures of things inside the ECU that seem to look different than everything else. Any body know if this looks bad or not?

-IC8 looks burnt up?
-There were a couple of these little green squares. Are they supposed to be that color or was that a reason to something?
-r69 and j1 looks like it's bridged. Is it supposed to be or did it melt down and connect accidentally?
-there was a small spot of corrosion that Tom pointed out but said t probably wouldn't effect anything right now. He cleaned it for me.


I am going to go do some more testing of the wires that Steve recommended later today.

Ic8 just looks like conformal coating used from the factory.
R69 & j1 looks like a previous repair. You can see someone intentionally scratched out the trace between j1 & r68. I couldn't tell you why.
I would trust Tom @ ECMTuning

I have used up all of the fuses in the county so I have decided to just bite the bullet and start undoing the harness and trace it back.

So far this is what I have found but I'm not sure if any of this would have cause the fuse to blow.

Is the long bare wire coming out of the shielded wire ment to be attach to something?

Also, I think it's something with this harness if it's a harness thing since this is the one that feeds most of the sensors, but is it worth pulling out the driver side harness as well or should I do one at a time and check?

So now after going through and coating every bare ware section with liquid electrical tape and either electrical tape or heat shrink, my car cranks but doesn't start and I cannot connect to ECMlink...I did find that the previous attempted repair on the knock sensor wire at the ECU plug end didn't hold up with all the beating that it took upon installation, but I don't think that should cause this issue...

So now you're back to square one but you're not currently blowing fuses.

What does the CEL and boost gauge do when you turn the ignition on?
Have you checked that you're getting battery voltage to the backup power and to the MPI/MFI relay?
Are you getting battery voltage to the ECU pin 82 when you turn the ignition on?

steve said:

So now you're back to square one...

Click to expand...

And a dreadful square it has been!


CEL is off and Boost Gauge reads 0. I did notice that my engine light doesn't come on at all like it normally does for a couple of seconds before turning off.

I am getting .15v at ecu power wires using the ground wires as well (pins 12, 13, 25, 26).

About 12v to bach k up power pin.

It doesn't seem like I'm getting power to pin 82.

I'm getting power to the relay that has the red wires (.15v and 12v) but am not getting anything to the one with the black wires.

I did just recently replace my ignition switch (before this whole mess) because there was an issue where I might have to turn the key off and on a couple times before it would actually engage when turning the key to crank the engine. I assumed that it wasn't part of the problem, but now I'm wondering if there is a short or something going on with that side of the harness as well.

I can take a video if that would help.

Try working through this and see if you can figure out what's broken. https://www.dsmtuners.com/threads/2g-basic-ecu-mfi-mpi-relay-circuit-function.497188/

So based on what I read I ended up double checking the BW wire at the ignition switch plug when the key is ON and I was getting 12v from that. I then probed pin 82 at the ECU with the key on and got 0v. I am thinking that this means that I have yet another short only this time it is conveniently in a wire that goes to, what appears to be, basically EVERYTHING...It also is the harness that I was hoping to not have to deal with since it means I have to pull the dashboard. Would you say that there is an easier/better way of doing this other than pulling the entire dash out?

EDIT: actually, now that I think about it, my hazard switch has not worked for a while, and I tried replacing it with a different junk yard box. Could this be linked somehow?

Start by looking at the things you have already been messing with so you don't make new problems. It might help for you to make a list of the things involved and check them off one by one.

I'll leave it to you to look at the electrical diagrams and figure out if the two are somehow related.

So I may have found the issue but I wanted to get confirmation that I am thinking correctly before I go tearing more stuff apart. I tested the BW wire going to the ignition switch plug and found that it has ground continuity. I then pulled connector b-75 on the back of the junction box because I saw a BW wire going to that and assumed its the same one. It did not have continuity with the ignition switch plug. However, this plug does not have ground continuity. I pulled fuse #8 at the junction box, the ground continuity goes away. I am assuming that means that there is another short somewhere. Fuse #8 looks like it powers the following systems: Auto-cruise control main switch, auto-cruise control, vacuum pump”2, auto-cruise-ECU*2, combination meter, ETACS-ECU, motor antenna assembly, SRS-ECU. My thought is to go plug by plug on these systems to see when continuity goes away and that will tell me specifically what wire is getting shorted. Does my logic make sense? I am definitely not confident in electrical stuff, so I am trying to learn how to diagnose this kind of stuff.

EDIT: actually, I was just realizing that that would only prove that there's no internal circuit fault with those systems, but there could still be a break in the wire somewhere that's going to those plugs.

There are lots of places in the car where the same wire color is used but it's not the same wire. You need to refer to the electrical diagrams and sometimes make a leap of faith when a connection shows up in one diagram but not another but it's clear that there has to be a connection since parts of the connection list are the same. Then you can verify that leap with your multimeter.

You'll have to excuse me but I can't parse things that don't have paragraph breaks or punctuation anymore. And I don't have time today to edit your post so I can follow what you're trying to say.

Apologies, I am deciding to bite the bullet and take the dash out. My thought is that there seems to be enough electrical issues that warrant me going over everything just to be sure.

This will also make any future diagnosing easier for me and anyone else that's helping.

And my suggestion remains don't until you have proven you need to. Too many people have just opened a new can of worms by messing with things that didn't require it.

Oh no, what have I done! Lol

Harness looked fairly decent after going over it once. I have not broken into the factory splices yet to see if there's anything that looks corroded but I will do that as I re-sleep everything with better loom.

There were a couple things that did not look factory to me and so I wanted to put them here to see if anyone can make sense of why these are here and if it's worth me removing them.

For some reason there is an inline 7.5 amp fuse on the wire that goes to the airbag module plug, One of the big white plugs down near the inside fuse box, and the three-pin plug up on the column. The fuse was blown so I'm wondering if this is why some of the stuff was not working. If it's not factory then I don't see any sense in keeping it. So would you all suggest just removing it and splicing the wires back together?

I also saw this Blue and black relay with a green and black wire going to it. The green wire seems to go to a clear 4-pin connector near grounding wires which may have something to do with HVAC. The black wire goes to one of those weird white plug things pictured below.

I'm assuming that red wire that's spliced off? The blue wire has something to do with an old sound system. So I may just go ahead and remove that.

Finally, there is the two pin plug that I found that I believe is for the blower motor. It is definitely done .

I will continue to post as I find more stuff.


EDIT: Upon further research I am wondering if the fuse was put in place for some kind of aftermarket alarm system. I think the wire may be the horn.

I just noticed on my ignition switch plug that it appears the plastic housing piece that separates the white wire pin from the blue/black wire pin is gone and their is a small amount on brownish burny looking stuff. Could this be what is causing the issue? This is not normal correct?

So I just put everything back in and turned the key to a no start crank. I found that the added inline 7.5amp fuse listed above blew again...it CANT be anything in this harness but it's blowing when I plug in the 3 pin horn plug under the steering column. But should this cause a crank but no start and not being able to connect to ECM link?


What are the chances that its inside my fuse box? I have no idea what else it could be that's keeping my ECU from working...

jdxnc said:

It sounds like it's breaking up but my bigger concern would be your oil pressure gauge is very low and the the dummy light is flashing.

Click to expand...

Just switch out my oil pressure sensor and I didn't in fact have the connectors reversed...I can't test it yet since my car still hasn't been fixed but I'm sure that's what was causing the flashing dummy light.

UPDATE: I finished up the harnesses and there are officially no fuses blowing.

1. @steve , I rechecked the MPI circuit and it seems that
-power is getting to the non-fuel-related relay, power is getting to the backup power on the ECU.
-Power is getting to the ignition switch and coming out on both BR and BW wires but not getting to the ECU via pin 82(I think, whichever is the ignition one).
-There is continuity between the ECU side of the BW wire and the ignition side of the BW wire.

I notice when I turn the key to start, voltage on the ignition switch drops to like 9.5 and I'm not sure if this is normal.

I also am still having that issue where my ignition switch doesn't reliably get my car to crank. Sometimes I have to sit there and keep turning the key back and forth until it actually engages.

2. My plan right now is to test the following since this is where the Blk/Wht wire runs to.
junction block (6)
fuse box B-51 (20)
fuse box B-49 (6)
fuse box B-66 (7) & (5)
fuse box B-75 (4)
Ignition switch (2)
fuel pump relay (3) & (4)
Ignition coil (3)
Ignition power transistor (6)
capacitor
combination meter C-06 (10)
Vehicle speed sensor (1)
ECU Pin 82

3. Also for Steve, as much as I hate to admit it, the following thread was me...Is it possible that I did infact fry something that is connected to the engine speed test connector that is also tied to the Bld/Wht wire? It looks like there are a couple places where they both run to the same thing?

Nevermind...the added inline fuse blew again

After testing the above, I found that there is no power to fuel side of the MPI relay, Ignition coil plug, PTU plug, Capacitor, VSS, or ECU pin 82. I also noticed that the terminals on the VSS plug are VERY corroded, and I am wondering if that could be a symptom of me accidentally connecting 12v to the RPM test connector instead of the fuel pump connector in the above linked post.


UPDATE: CAR HASS STARTED! The problem was the same issue that was in this post.



However, there are now 3 new problems.

Problem 1: now my coolant temp is not reading and my dash stopped working while the car was still running. When I jiggled the inside fusebox everything came back so I am assuming a short there somewhere?

Problem 2, my rpm's are reading 0 in ecmlink?

Problem 3: ISCPosition does not seem to change when adjusting BISS.