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Discussion Starter #1
Hey guys, I’m new to the forum but not new to the car. I’ve had my Blue 94 for a while now, since 2010. It ran into a few problems when I was in college and didn’t have the money to fix it. But now I’ve come around into some extra cash and started to resurrect this thing.

here’s a little backstory. It’s been sitting in my driveway for about 6 years, mostly due to it overheating and leaking power steering fluid. The tranny is going to need a rebuild as well, but that can happen after I get the thing back on the road.

So the overheating issue is kind of weird to me. It had a leaking radiator hose, so I replaced both of them and the thermostat, and put all new fluid in plus the water wetter. I got the kit from 3SX. Note the inside of the thermostat housing is DISGUSTING. Definitely will replace that at some point, for now I cleaned it out the best I could.

I started it up and it ran fine for about 20 minutes. GREAT!....nope lol all the sudden it started to overheat 20 minutes in. I get out and neither fans are spinning. I then turned the heat/AC on and the driver side fan kicks. The temp started to go back down and it won’t overheat from idle and some moderate revving with the heat on. So I know that fan spins when it’s given power.

So as of now every time I start the car this what happens.

Runs great for 10-20 minutes and no fans spin. The only thing that’s making any spin is turning the heat on, and it’s only the driver side.

I checked for voltage at the connector that goes to the passenger side fan. I didn’t get anything there while it was overheating. I am thinking it’s the coolant temp sensor for ECU since neither are turning on at their temp setting. I don’t want to just start replacing stuff though.

Any thoughts here?
 

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93 NA ATX 3000gt DOHC
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.....I checked for voltage at the connector that goes to the passenger side fan. I didn’t get anything there while it was overheating.....
Was the wire you check Red wire with black stripe or Blue wire with green stripe? Shouldn’t even need key on to show battery voltage on these.
 

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Discussion Starter #3
Was the wire you check Red wire with black stripe or Blue wire with green stripe? Shouldn’t even need key on to show battery voltage on these.
This was a blue wire with green stripe. It read around maybe .03V, I assume that is not the number it should be reading.

Just for funsies I checked the other wire that was there for power AND ground without any reading

I checked the main power and ground wires as well, they were fine.
 

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This was a blue wire with green stripe. It read around maybe .03V, I assume that is not the number it should be reading.
Did you check the Red wire with black stripe? Should be near wire with .03V reading.

Just for funsies I checked the other wire that was there for power AND ground without any reading
Not sure what you mean by wire for power AND ground.:unsure:
 

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Discussion Starter #5
Did you check the Red wire with black stripe? Should be near wire with .03V reading.

Not sure what you mean by wire for power AND ground.:unsure:
So I just tested them all again with the key off.

Red with black stripe was 12.84V
Black was 12.84V to Positive
Blue with green strip was .03V
Blue with yellow showed no voltage
 

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OK.. Not completely sure about Blue/green reading of .03v but might be an explanation for that, but others seem correct.

To test your fan just leave key off. Removed fan low speed relay, fourth one from front of car on longest row of relays. Use jumper wire across largest two pin sockets. If fan runs that will indicate relay is not pulling in and we’ll need to troubleshoot that circuit.
 

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Discussion Starter #7
OK.. Not completely sure about Blue/green reading of .03v but might be an explanation for that, but others seem correct.

To test your fan just leave key off. Removed fan low speed relay, fourth one from front of car on longest row of relays. Use jumper wire across largest two pin sockets. If fan runs that will indicate relay is not pulling in and we’ll need to troubleshoot that circuit.
Thank you. I'll get to doing that tomorrow.

I do have a question. Even if the low speed isn't turning on wouldn't the high speed turn on when it got to 203 degrees? Neither the driver side or the passenger side fan turn on due to temp

The only one that turns on is the driver side and that is ONLY when the Heat/AC is on.
 

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The high speed would come on at some point but not sure what temp is programmed in ECU, but 203 degrees seems a little low to me. It’s normal for drivers side to run when A/C turned on. ECU only controls high speed on that fan and passenger side fan.

The test is just to eliminate fan or resistor as a problem, then well know if it’s in those or relay or ECU. While your at it you could pull 7th relay back in same row (fan high speed) and use jumper to test fan in high speed.
 

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Discussion Starter #9
I see what you're saying and I am definitely going to check that first.

I guess what my point is is that since both the fans are not turning on when they should wouldn't that eliminate the relay for each one? I suppose both of them could have a bad relay, just seems unlikely to me, but with it sitting for so long i would not be too surprised lol
 

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Yes, two relays bad is unlikely but not sure high speed set point has been reached to turn on A/C fan in high. I'm most concern that regular fan motor might be bad or resistor in that curcuit. If fan works after jumping it, you could swap relays and if low speed comes on at temp you'll know that relay was the problem.
 

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Discussion Starter #11
Yes, two relays bad is unlikely but not sure high speed set point has been reached to turn on A/C fan in high. I'm most concern that regular fan motor might be bad or resistor in that curcuit. If fan works after jumping it, you could swap relays and if low speed comes on at temp you'll know that relay was the problem.
The stock temp gauge was fully redlined and the A/C fan never turned on at all. So i would assume that it was high enough. I used 203F because I read that in another thread, not sure if its correct. the passenger side didn't turn on either. The point is the car was overheating and neither fan turned on. I will still test both the fans and relays just to be safe.

A/C fan (drivers side) turns on when the A/C is on, so i know that fan works when given power.
 

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I understand what your saying and it has good logic. There’s a chance ECU has a problem (not grounding transistors) or temp sensor for ECU has a problem. But I suspect if temp sensor was the problem your engine wouldn’t be running properly. There’s also chance you’ve got air bubble in system that’s keeping coolant from getting to temp sensor causing it to send incorrect data to ECU. I’d just like to eliminate fan motor problem first since simple jumper can do that.
 

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Keep in mind that the temp gauge uses its own temp sensor so that could cause the gauge to read incorrectly (indicate hotter than it actually is for example).
 

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Discussion Starter #14
I understand what your saying and it has good logic. There’s a chance ECU has a problem (not grounding transistors) or temp sensor for ECU has a problem. But I suspect if temp sensor was the problem your engine wouldn’t be running properly. There’s also chance you’ve got air bubble in system that’s keeping coolant from getting to temp sensor causing it to send incorrect data to ECU. I’d just like to eliminate fan motor problem first since simple jumper can do that.
Fair enough and solid point about the car not running well if that were the case I think there is a good possibility that there is a little air in the system. I'm going to try to bleed it through the coolant cap for the 3rd time tomorrow and test the relays and the fan motor.
 

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Discussion Starter #15
Keep in mind that the temp gauge uses its own temp sensor so that could cause the gauge to read incorrectly (indicate hotter than it actually is for example).
I was thinking about this as well, it seems like its accurate. whenever i turn the A/C on and that fans kicks on the gauge starts going back down. might be a little off but it seems to be working as it should.
 

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I was thinking about this as well, it seems like its accurate. whenever i turn the A/C on and that fans kicks on the gauge starts going back down. might be a little off but it seems to be working as it should.
Even sitting at 180F at idle if I turn on the high speed fans the temp will keep dropping on mine so just because the needle goes down doesnt mean much unfortunately. Might be worth it to figure out exactly what the temp is at when the needle shows high (after making sure the fans work).
 

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If test you’re doing today shows no problems, I’ll add another test that will test entire fan circuit including wiring, relay, relay control circuit, etc. all the way up to ECU. That will eliminate every thing but ECU and data from temp sensor. It will require you to remove console/hump carpet from drivers’ side to get to ECU plugs.

You’ll need something like straight pin to slide in back side of pins of ECU connector and jumper wire that can be used to connect that straight pin to good ground.

You’ll need ignition switch turned ON for this to work.

1) Ground pin 6 of ECU (GREEN/yellow wire), Passenger side fan should run in low speed.
2) Ground pin 53 of ECU (BLUE/red wire), Passenger side fan should run in high and most likely drivers side fan will also run in high.

Depending on these results might have to move on to temp sensor test and if that checks out, good chance problem is within ECU.

94-97 ECU pins.JPG
 

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Discussion Starter #18
If test you’re doing today shows no problems, I’ll add another test that will test entire fan circuit including wiring, relay, relay control circuit, etc. all the way up to ECU. That will eliminate every thing but ECU and data from temp sensor. It will require you to remove console/hump carpet from drivers’ side to get to ECU plugs.

You’ll need something like straight pin to slide in back side of pins of ECU connector and jumper wire that can be used to connect that straight pin to good ground.

You’ll need ignition switch turned ON for this to work.

1) Ground pin 6 of ECU (GREEN/yellow wire), Passenger side fan should run in low speed.
2) Ground pin 53 of ECU (BLUE/red wire), Passenger side fan should run in high and most likely drivers side fan will also run in high.

Depending on these results might have to move on to temp sensor test and if that checks out, good chance problem is within ECU.

View attachment 287072
So I found the problem. Believe it or not it was both relays. I shorted the circuits at the relay box and the passenger fan kicked on for both low and high speed. From there I let the car run and start to overheat. Once it started to I checked to see if the relays were getting the voltage to "click", they were. Then I just popped in the fog light relay in the low and high speed spots and they both kicked on.

Thanks for all the help, had that not worked the information you gave me here would have been a huge help.
 

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Discussion Starter #19
Even sitting at 180F at idle if I turn on the high speed fans the temp will keep dropping on mine so just because the needle goes down doesnt mean much unfortunately. Might be worth it to figure out exactly what the temp is at when the needle shows high (after making sure the fans work).
That is very interesting, I will most certainly keep that in mind if anything else goes wrong with it. I ended up finding out it actually was both of the relays
 

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So I found the problem. Believe it or not it was both relays. I shorted the circuits at the relay box and the passenger fan kicked on for both low and high speed. From there I let the car run and start to overheat. Once it started to I checked to see if the relays were getting the voltage to "click", they were. Then I just popped in the fog light relay in the low and high speed spots and they both kicked on.

Thanks for all the help, had that not worked the information you gave me here would have been a huge help.
(y)
Good to hear you were able to run it down, just goes to show unlikely possibilities can sometimes throw anyone off like you and me. But that's why testing is better than machine gunning parts in hopes of hitting target.

You’re more than welcome for the help.
 
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