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1G Car keeps randomly dying on cold start!!!

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Red_EcliPzE_GsX

20+ Year Contributor
124
42
Nov 25, 2002
Irving, Texas
Guys, I am so lost and frustrated at the issue I’ve been having with the car for a good while now.

90 gsx 5 speed non eprom ecu. It will just completely die on a cold start when it seems to be chilly/cold outside.

I’m not talking sputter and die I mean it straight cuts off like if I turned the ignition off. I don’t know what the hell it could be.

Symptoms:
-first noticed when weather was colder, and only on cold starts
-soon as it got to normal operating temp it would stop doing it
-on normal warm days it would not die at all on cold starts.
-when it dies I lose my check engine light, but if I turn the ignition off/on again it comes back.
-even trying to keep it at a steady higher rev, it will just straight cut off on me as well.
-buddy told me to try unplugging the coolant sensor switch on a cold start to see if it would turn on, to confirm if my coolant sensor switch was bad? I unplugged it, and the car did not want to start at all, it would just sputter really bad. Plugged the sensor back in and then it would turn right on for me, but then of course cut off and die like it does.

As time has gone on though, it seems to have gotten worse.
-it now will do it even when it first gets to operating temp and I attempt to drive off for the first time, literally just dies while I’m in gear going
-just now even after it seemed to finally be acting right long after being at operating temp, just pulling into my complex it just died.

Things I’ve checked:
-my PTU has been replaced with a 91+ when I first noticed I was getting no check engine light with key in on position. I just spliced the wires to work.
-sent ecu off to ecmlink, they said it tested fine but the caps looked like they had been replaced before but could have done a better job, so they replaced caps, tested fine afterwards and even put it in a test car and ecu still fine.
-I’ve done basic things like check plugs, I regapped plugs and have some new ngk wires on the way tomorrow. However I don’t think that is going to help.

here is a video so you can see for yourself. This is about the 15th time of me turning it on again you can see on the temp gauge that it’s still on the colder side(I had just tried turning it on again after it sitting for a few hours from the last time I drove it)

you can hear how it just cuts off completely, wait til end of video and you can see how it’ll even happen if I try to hold a steady rev, and then you can see the check engine light lose its shit.

As I watch the video I notice it seems to die immediately as I hear this click sound?? Not sure where it’s coming from. I know it sounds like I hear it in the car but not sure from where.

I don’t know what else to do!!

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Last edited:
That’s what I was thinking it might be after reading a few other threads on here. I have a cousin with a 93 gsx, would it be easier pulling his mpi relay off his and testing it on mine? Or is there a difference in year for mpi relay from the bastard 90s and the 91-94?
Could it be a bad MPI relay?

Ya have someone start the engine while you touch the MPI/FP relay to see if it clicks off when it dies. Of course if it does, it may be the ECU telling it to which you'll have to check (MPI pin 8, BLK-BLU wire going back to +12v which turns off the MPI relay {0v there turns it on}).
 
check gap in plugs use a feeler gauge not that coin crap also maybe do a ECU reset and check MFI Relay

mine does the complete shutoff too! but its when driving and hitting 4500 to 5000 it did the exact same thing yours is doing complete shutoff i still haven't figured it out yet
 
check gap in plugs use a feeler gauge not that coin crap also maybe do a ECU reset and check MFI Relay

mine does the complete shutoff too! but its when driving and hitting 4500 to 5000 it did the exact same thing yours is doing complete shutoff i still haven't figured it out yet

Ah I had regapped my plugs with the coin yeah. Coin said they were 34-35 so I brought them down to 28, again on the coin.

How do I reset the ecu? If you mean unplugging the battery for a while I also did that yesterday left it unplugged for a few hours.
And for mpi relay I am going to try the above tip about feeling the mpi relay and if that’s the click I’m hearing right as it shuts off. I also want to try swapping out my cousins mpi relay from his 1g gsx as well.
 
Alright update guys, as I went to take a closer look at the mpi relay, it had duct tape all around it, so I figured that was a red flag. As I began to unravel it, the mpi relay just came apart from the gold box?? That can’t be good?

Now when I turn the ignition on, I get no CEL and boost needle doesn’t spike to zero. This has to be it right?

I’m going to get my hands on another 1g mpi relay and plug it in see what happens next.
 
My mechanic is working on my evo and I had him give your video a listen . He Said he can hear the relay clicking when your car turns off

That’s bad right? Like I mentioned I just removed duct tape off of it (from previous owner I’m assuming) and it came apart pretty much. Since then now I get no CEL with ignition on, which I know for sure won’t let me turn the car on.
 
There is a 90 turbo ECU for sale for $50 in the classifieds if you think the ECU is turning the relay off. Just noticed it.
 
Marty! But the ecu just recently came back from ecmlink with new caps and they said it tested out fine? And now that I started messing with the mpi relay I get no cel. Wouldn’t that be a bad mpi relay? My ecu shouldn’t be bad? I was assuming the click that can be heard in the video was the mpi relay?
 
Ah I had regapped my plugs with the coin yeah. Coin said they were 34-35 so I brought them down to 28, again on the coin.

How do I reset the ecu? If you mean unplugging the battery for a while I also did that yesterday left it unplugged for a few hours.
And for mpi relay I am going to try the above tip about feeling the mpi relay and if that’s the click I’m hearing right as it shuts off. I also want to try swapping out my cousins mpi relay from his 1g gsx as well.


Long ECU/ECM Reset Procedure
1. Disconnect Battery during install of your goodies (remove negative then positive leads) leave off for 20 mins

2. When done Reconnect Positive then Negative Leads

3. Turn Key to ON position (but do not start) for 2 minutes (you will hear clicking noises under the hood)

4. Turn key off for 10 seconds

5. Turn the car on and let it idle for at least 10 minutes (motor will run rough for awhile then it will smooth out)

6. Turn key off for 10 seconds

7. Turn on and take for test drive (be easy on the engine do not go above 3500RPM for first 30-40 miles)

8. Turn off engine for a few minutes, Start it back up and give it hell (drive for a bit to see if it will spit any codes from what was done, if it does turn car off and scan for codes
 
Reset ecu, plugged in a new mpi 20a fuse at positive batt terminal, and plugged in a working mpi relay from my cousins 1gb gsx, and cel came back on ignition, car cranked right up and hasn’t died yet.

Been testing it for some time now and all seems well. I’ll keep testing though. Thank you everyone!
 
you still good?
mine was a (engine fuse) the fuse contact points were failing so when I would rev or under load the vibration would cause it to die instant, bent my contacts a little out and re-put fuse back in an sparks are flying and its been fine ever since finicky little cars man I tell ya
 
you still good?
mine was a (engine fuse) the fuse contact points were failing so when I would rev or under load the vibration would cause it to die instant, bent my contacts a little out and re-put fuse back in an sparks are flying and its been fine ever since finicky little cars man I tell ya

Yes sir! Since replacing the MPI relay car has been just fine! Cranks right up each time and cold starts are perfect now. It is such a relief to finally be able to enjoy driving the car worry free! For now..
 
Glad to read you have fixed the problem, but I still can't fathom why the "cold" running failure would be related to the MPI relay, since it's operating conditions don't change with engine temp??
Exactly why electrical issues are so vexing! You can "fix" it and never understand why...
 
Glad to read you have fixed the problem, but I still can't fathom why the "cold" running failure would be related to the MPI relay, since it's operating conditions don't change with engine temp??
Exactly why electrical issues are so vexing! You can "fix" it and never understand why...
Cold shrinks and heat expands. Sometimes heat will be all a circuit needs to make contact. Electrical gremlins! It makes it hard sometimes to diagnose
 
Sure, that's true (except for water, since ice floats=expands on freezing :hmm:). So perhaps it was related to the relay itself warming up because of enough current flowing through it? It's mounted in the cabin, so engine temp would have little to no effect there. A relay typically is electro-mechanical, with moving contacts, as you pointed out. I suppose that could explain it, especially since it basically was being held together with tape. This is one reason that repair shops frequently play the diagnosis-by-replacing parts technique; just keep swapping stuff until it's fixed. I owned a 99 RAV4 that two dealerships failed to fix after several days and over 1K in parts, only to have a third shop figure out that the wire to the crank sensor was fraying internally, and for under $150 they fixed it. The level of complexity vs. advantages of more sophisticated systems (EFI, ABS, Torque Vectoring?!!) is one of the reasons I chose a DSM to be my long-awaited sports car project. It strikes a good balance between have modern features without touch screens and lane departure B.S. The shop manual takes two volumes, where the latest cars now can't even print paper volumes of the manual, as they would take up a file cabinet. You practically need an I.T. department to even open the hood. Terms like "wrenching" and even "Mechanic" are becoming outdated, as we move toward shops full of "Technicians"!
 
I honestly think it could have been me that did it. When I was first messing with the ecu taking it in and out(back when I thought it could have been the ecu doing it) shaking things up in there, it started to happen more frequently. But then stopped for a while. Then more recently when I was trying to install the factory head unit, moving more things around in there, I noticed the 'duct taped' MPI relay and had hit it a few times while I was messing around in there.

Next thing you know it got worse where it would start happening regardless of cold start or operating temp and even while rolling in gear.

When I finally started trying to diagnose the relay, as soon as I took it out and removed the duct tape, it fell out of the gold casing. Fell apart in my hands. Taking a closer look at it I definitely noticed new soldering.

So I think this MPI relay had BEEN causing issues even for previous owner, he attempted to fix and then duct taped it back together instead of just replacing.

But anyways yeah car has been just fine since ordering a fresh good working condition relay and returning my cousins relay back to him that I had initially used for testing.
 
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