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Discussion Starter · #1 ·
1995 NA.
Car seems to have some odd wiring but was never an issue. Car died last summer, got it towed. Thought the ecu was shot,replaced ecu still having the same issue.

If key is turned to acc. The starter relay constantly buzzes, if I push the clutch in it will stop buzzing. Car cranks but will not start, no fuel no spark

If I turn the headlights on the headlight relay constantly buzzes and no lights come on, no power to windows, radio, etc

I've checked for shorts in the wiring and have not found any yet. All fuses are fine. Any ideas what else could cause this?
 

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93 NA ATX 3000gt DOHC
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If key is turned to acc. The starter relay constantly buzzes, if I push the clutch in it will stop buzzing. Car cranks but will not start, no fuel no spark
If you’re absolutely certain it is the starter relay buzzing when key is in ACC position, I’d say your problem is most likely the ignition switch itself has gone bad. I say that because the starter relay should only get power when key is turned to the (st) start position, and without any power there’s no way it could buzz.

Now if it’s a different relay or you’re wrong about the ACC position, it could be a completely different problem.
 

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SuperDON to the rescue!!!!

You go girl!!!!

Bob. ;)
 
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Discussion Starter · #4 ·
It's definitely the starter relay buzzing. It also buzzes when I turn the headlights on, head light relay also buzzes. Even without key in ignition both relays will buzz if headlight switch is turned on
 

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It's definitely the starter relay buzzing. It also buzzes when I turn the headlights on, head light relay also buzzes. Even without key in ignition both relays will buzz if headlight switch is turned on
Disconnected ignition switch, relays still buzz
That’s almost crazy, which causes me to ask few questions.

1) Does your car have a factory anti-theft system or an after market alarm system?
2) Has it had a click-click no start mod done to it, like maybe an added relay somewhere?
3) Is the braided ground strap between firewall and plenum support bracket still attached?
4) Any chance something was allowed to get under the relay/fuse box under the hood, like maybe a tool or something left in fender well that may have slid under it or mice built a nest under there?
 

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Discussion Starter · #7 ·
No factory alarm, there was an aftermarket one but I disconnected it.
No click start relay.
Braided ground was disconnected, re connected it and same issue
Nothing under fuse box, have it all pulled apart looking for shorts.

This is driving me crazy, I'm pretty good with electrical, (I do hvac) but this has me stumped
 

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Since you have things opened up, try disconnecting the ETACS unit to see if the buzzing stops. Wondering if there feed back some how thru that unit.
 

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What is etacs? And where is it located?
Don’t know what the actual letters stand for, but it’s mainly a body control unit that houses timers and supplies power or ground control for some components. IIRC it works in conjunction with the light auto-shut off unit which supplies control power to the headlight relay from a constant power source. It’s located under dash left of steering column with a 19 pin plug, probably near where you unplugged the ignition switch connector.
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This is driving me crazy, I'm pretty good with electrical, (I do hvac) but this has me stumped
I can certainly see why it’s driving you crazy; I can’t imagine how even a minimal voltage is getting to starter relay to cause it to buzz without key turned to start position. Unless wiring changes were made with aftermarket alarm unit that you haven’t completely got redone when removing it. Nor can I imagine how turning headlight switch to on could in someway supply minimal power to starter relay to cause it to buzz.

If you don’t already have the electrical diagrams, you can down load them free from below link. It would be Volume 2 of the listed “1992-1996 Service Manual - 3000GT” Vol. 2 .... It does have some line & lettering faults when it was converted to PDF format, but can be made out for the most part.
 

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Since you have things opened up, try disconnecting the ETACS unit to see if the buzzing stops.
Ok thanks, I'll check it tomorrow
After looking at prints, I now suspect unplugging the ETACS would be a waste of time. It is more involved with headlight pop up and down on 1st gen cars which your 2nd gen doesn’t have. I couldn’t identify any direct connection to headlight bulb operation or any possible path to the starter relay, sorry about suggestion to unplug it.

Hard to suggest proper path of evaluation, but I do feel the key is finding source of low voltage to starter relay control coil when headlight switch is turned on. I think when that is identified and fixed that other problems will also be cured. I also can’t help but think the aftermarket alarm wiring was somehow involved.
 

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Discussion Starter · #14 ·
Does anyone know why this may have been wired like this? Someone told me it's not factory. 2 black wires spliced into the stranded part of the green wire. There's a few spots wired like that at the ecu.
Also wanted to mention that all the buzzing noises I've explained still happen with ecu disconnected. Not sure if I should have power to anything without ecu hooked up?
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Also wanted to mention that all the buzzing noises I've explained still happen with ecu disconnected. Not sure if I should have power to anything without ecu hooked up?
Wanted to address this first before wiring, because I think it is important in your troubleshooting. You will have battery positive power (~ 12v) to almost ever component that needs it, without the ECU hooked up. The ECU is not designed to supply 12v to needed components, which is handled by fuses, relays and some switches. The ECU will in many cases supplies 5v to several components that it monitors for voltage changes or pulses for input it combines with internal logic, to control components mostly (not all) by switching grounds ON and OFF to control that component. The switching of grounds on and off on circuits does sometimes cause confusion, because when a circuit is not completed (ground made) you can often read ~12v at ECU grounding pin for that circuit, which will drop to a very low voltage when ECU internal grounds that circuit. The ECU does receive 12v supply on ~4 pins it uses to power it’s internal systems, one constant for temporary memory retention, one switched (ignition switch) and two when MFI relay is closed.

The below attached connector pin# location can help, if you can identify pin#’s that a questionable wire is hooked to. I’ve also included what I believe to be correct pin-out descriptions for you ECU, which I think is same as 1st gen ECU’s (didn't change until '96), if incorrect I suspect and welcome any correction by better informed individuals here.
(Click on images to enlarge)
296167

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Does anyone know why this may have been wired like this? Someone told me it's not factory. 2 black wires spliced into the stranded part of the green wire. There's a few spots wired like that at the ecu.
Now to that wiring, I don’t actually remember seeing that splicing of 2 black wires to what appears to be shielding from the large green wire and shielded white wire. Even though I’ve never noticed it, in prints the O2 sensor wiring appears to be shield and shows one black wire grounded, but not both. Though print is missing some detail, it appears the black wire from within the shielding should be hooked to ECU pin 72 and white wire :unsure: should be to pin 56. The other black wire would go to a ground, possible along with the shield braiding I assume. Can’t tell from picture but looks like some wire from shield braiding might go to ground:unsure:. In summery maybe a factory splice that has been tampered with:unsure:, but you mentioned few spots like this and as far as I know NA engines only have one O2 sensor.
1626997484871.png Click to enlarge

Edit: However after looking at print again, the shield black wire to ECU pin 72 does get grounded internal by ECU when it wants to do so, which means end results is both black wires does end up grounded. Not sure what permanently grounding black wire to 72 would do, possibly eliminate open loop operation :unsure:. Step up Ex-spurts. :)
 

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I have power on the stranded shield wire. I'm thinking that's where my issue may be
Yeah… that doesn’t seem right; try disconnecting the black wire from inside of shielded large green wire from the spliced area and see if you drop power on braided shielding.
 

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I’ve also included what I believe to be correct pin-out descriptions for you ECU, which I think is same as 1st gen ECU’s (didn't change until '96), if incorrect I suspect and welcome any correction by better informed individuals here.
Dunno if I'm "better informed" but the wiring changed with each ECU change. So it changed in 94, and then again in 98. So 91-93 have the same pin-out, 94-97 have the same pin-out, and then 98/99 have the same pin-out.
 
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