DSMTalk Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum banner
Cancel
Create thread New Garage Forums

Bad ECU?

Jump to Latest
1 - 16 of 16 Posts
L

lithium

· Registered
Joined
·
699 Posts
Discussion starter · #1 ·
Well, through my basic troubleshooting, I think I'm lead to a bad ECU. My car was running fine one night, I turned it off, went to start it the next day, and it'll crank fine, but won't start. After replacing the MPI relay, I started checking circuits when I noticed my CEL wasn't coming on. So I went to see if it was just the light being burnt out, and coincidence, or if there was a problem at the ECU. I went to see if the ECU had any codes, and NOTHING. I get no voltage at ALL from the MPI diagnostic port. From what I've been told, the ECU does spit out a code even if it's functioning properly with no errors, and should even spit out a code if the problem is ECU related... I get NOTHING AT ALL. Does anyone have any experience with this that can verify I need a new ECU?

Thanks,

-Craig
 
#2 ·
Have you checked the MPI fuse? I had two ecu's go out on me. THey will cause your car to stall, but it'll usually refire in a few minutes and get you home. I've yet to have one stop and not come back enough to get me home.
 
#3 ·
Just had this happen in my buddies 95.... I know not the same but close... just check all the clear top'd fuses under the hood, either altenator or motor is blown most likely... *shrug* I hope the setups arent that different that I sound like an ass :p

hope it helps
 
Save
Reply Quote Like Like
Discussion starter · #5 ·
Hey guys.. thanks for all the replies! I checked EVERY fuse in the car, including all fusible links under the hood.... they're all good :-( The car is acting as if the room/plafon fuse is out almost. It's very strange. The alternator shouldn't have any effect on the car starting, I wouldn't think, as the battery has more than a sufficient charge to turn the car over... it just won't fire.

Thanks again guys,

any more suggestions would be greatly appreciated.

I'm kinda at a loss here, everyone tells me the car would act a little differently if the ECU was toast.

-Craig
 
#6 ·
open up the ECU and see if there is visible damage... ie. Black or Brown burn spots around the caps, or anywhere.... or see if it smells bad, that also is a hint of bad caps, which probably means bad ECU.....
 
Save
Reply Quote Like Like
Discussion starter · #7 · (Edited)
IT STARTED!

Ok, here's the deal... I hope someone knows the answer to my question... The car started today. After numerous troublesome diagnostic hours, I found out that there are two pinouts on the ECU for power. One is pin 103, which is a constant 12v power supply (backup) so the ECU can retain memory when the car is off. The other is pin 102, which is a 12v power supply when the ignition is turned to the ON position. On the wiring harness, pin 102 has no voltage output at all, regardless of key position. I used a separate 12v power supply to feed pin 102 into the ECU, and the car started! I can get a CEL when the key is in the ON position now, also. My question is this.... is there any HIDDEN relay/fuse that's directly related to the wire that leads to pin 102 on the ECU. I've checked EVERY VISIBLE FUSE in the car, including all fusible links in the engine compartment, and ALL test fine for continuity. BTW: I just put a new MPI relay in thinking that was my problem initially, and neither the old one, or the new one, have any effect getting power to that wire. I don't want to have to remove my entire dashboard to trace that wire from the ECU to wherever it goes if I can avoid it. Anyone who knows the 1st gen DSM wiring harness, this question goes out to you! I'm assuming this wire is connected in some way to the ignition switch (hence the power it's supposed to get when the car is turned on); could I possibly have a faulty ignition switch?


-Craig
 
#8 ·
if its faulty ignition switch then NOTHING that turns on while the car is running should function, ex. cigarette lighter, windshield wipers, ac compressor, windows( in ACC), radio (in ACC) uhm, heater... cant think of anything else off the top of my head, but that would be what I would say... does other ON only items work with this fix? or only the ECU and its lights?
 
Save
Reply Quote Like Like
Discussion starter · #9 ·
The only thing that doesn't work with the ignition switch in the ON position is the ECU POWER, and associated CEL as far as I know. I just wasn't sure if there was a separate lead specifically for ECU coming from the ignition switch that maybe wasn't working. I know the switch sends current to all accessories.

Thanks,

-Craig
 
#10 ·
This brings me back to saying something about that harness that was unplugged. That harness sent power to the ecu. The wiring setup of the harness is as follows:

(Blk-Red) (Blu-Blk) (Empty) (Blk-Red) (Empty)
(Grn-Red)(Blk-Whi)(Yellow) (Empty) (Blk-Whi)

Hopefully this helps.
Mike
 
Discussion starter · #11 ·
Hey... what harness was this again that you're talking about? and where did you find it, roughly? This will at least give me a start to tracing the power from the ECU through the car to find the problem.

Thanks again for all your help man.

-Craig
 
Discussion starter · #12 ·
Oh yea... the one in the engine bay. I checked that, and it was plugged in. I believe it's the one located under the relay terminal near the battery, correct? I'll go test both sides of it and see if maybe I'm not making a good connection in that harness or something.

-Craig
 
Discussion starter · #13 ·
Oh yea, should the MPI relay click when the key goes to ON? I think I remember it used to, but now the only click I get from that relay is when I turn the key to START, and then again when I turn the key to ACC/OFF. The clicking is no longer consistent with what I used to get, either.... it used to click about 10 seconds after I turned the switch off, now it clicks about 2-3 seconds after. The fuckt up part is I just replaced this relay 3 days ago, when this problem first strated, with a brand new relay from SATAN, so I guess it must be something to do with power BEFORE this relay.

-Craig
 
Discussion starter · #14 ·
Figured it out!

Hrmph, must be a problem unique to me, but the MPI relay wasn't getting grounded. I messed with the connector and tightened the terminals, and sure enough, the car starts every time. Hope my hours and hours and hours of troubleshooting can help someone out sometime. It just wasn't making sense to me, the relay was getting juice, and the ECU wasn't... turned out to be a simple bad ground.

-Craig
 
Discussion starter · #15 ·
I just re-read what I wrote, and should be a little more specific in case anyone cares. I'm not referring to any connection in the engine compartment when I refeer to the MPI RELAY ground. The plug that goes INTO the relay was not getting ground to it, after messing with the connector a bit, cleaning the contacts, and making the contact slightly tighter on the prong, I think I fixed the problom.

Thanks for all the help, the car ran great all night.


-Craig
 
1 - 16 of 16 Posts
About this Discussion
15 Replies
6 Participants
Last post:
vr4gazm
DSMTalk Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum
posts
2.3M
members
104K
Since
2000
A forum community dedicated to Mitsubishi Eclipse, Plymouth Laser and Eagle Talon owners and enthusiasts. Come join the discussion about performance, turbos, builds, modifications, troubleshooting, maintenance, and more!
Full Forum Listing
Explore Our Forums
General DSM Tech and Tuning Help! Tech Newbie Questions Forum Body Tech and Appearance Electronics Tech