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So a while back I picked up an sl to get something different and it was an auto with only 1 gear because the trans was shot, so I thought it was a perfect time to swap it and get a bunch of experience working on it. So over a pretty long period of time around 6 months I’ve been accumulating everything and slowly putting it all together and yesterday with the help of a friend we got the transmission in, we bled the clutch, and replaced all the fluids. Oh and also a brand new starter. So we wanted to start it without the cv axles to see if the clutch would engage and disengage like it’s supposed to but when we go to start it it wouldn’t even turn over. It was just a click from the charcoal canister. So we remembered about the safety switch that was on the auto and we plugged it in to the ecu and turned it and it turned over. Now it didn’t run good at ALL I don’t have the tac In so I’m not sure on the rpms but it was hardly running and for some reason it would rev up high without me pushing the throttle, almost like it was trying to stay alive. So we made sure all the 02 sensors were in and all the connectors we could find but it still just running rough so I gave up for now to not cause damage. Any ideas? Help would be greatly appreciated by anyone
 

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Also I forgot to mention, new spark plugs gapped correctly I believe, I cleaned the plenum of all the carbon buildup and hooked it back up the correct way, it’s getting power, on the gauge it says 12v but I don’t even hear the fuel pump kick on before I start it. Now it is a stock fuel pump and I’m not sure if it’s really loud enough to hear but it’s silent. So we checked the relay and they seem to be fine, I’m not 100% sure but they don’t look burnt or anything. And before the swap it would turn over fine.
 

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Flasher
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What do you mean you plugged the safety switch into the ECU?
 
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93 NA ATX 3000gt DOHC
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What do you mean you plugged the safety switch into the ECU?
So the auto had its own “safety switch” so you could only turn it on in park basically and when I plugged that in I was able to turn it over
Don't know where on ECU you made that connection, nor what year your car is and trim level (theft alarm - no theft alarm, etc.) because you didn't include that info.

BUT, I can tell you using ECU in any way to control starter solenoid is probably one of worst things you could do. Not only could it cause a problem with ECU operation, it could possibly damage it.
 

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Don't know where on ECU you made that connection, nor what year your car is and trim level (theft alarm - no theft alarm, etc.) because you didn't include that info.

BUT, I can tell you using ECU in any way to control starter solenoid is probably one of worst things you could do. Not only could it cause a problem with ECU operation, it could possibly damage it.
I'm not familiar with the 3/S auto trans but what I believe the OP is trying to say is that they wired in the park/neutral safety switch and then the car would turn over by the key, not that they connected the wire and it caused the starter relay to turn on. I think OP just worded it poorly. But this makes me wonder if the wiring for the park/neutral safety is basically the same as the clutch safety switch, and if OP wired that up or not.
 

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I'm not familiar with the 3/S auto trans but what I believe the OP is trying to say is that they wired in the park/neutral safety switch and then the car would turn over by the key, not that they connected the wire and it caused the starter relay to turn on. I think OP just worded it poorly. But this makes me wonder if the wiring for the park/neutral safety is basically the same as the clutch safety switch, and if OP wired that up or not.
You might be correct if he basically tied wire before Automatic safety switch to the wire leaving it together the ECU wouldn’t be evolved. But he indicated “about the safety switch that was on the auto and we plugged it in to the ecu and turned it and it turned over”, that would cause the entire current draw of starter solenoid to pass thru the ECU :eek:. The difference in manual trans is only starter relay control power passes thru clutch switch to ground, which is only the current load needed to engage the starter relay, which isn’t a high load and only happens if clutch isn’t pressed.

The automatic cars doesn’t have a starter relay, wire from ignition switch runs directly to P/N safety switch and on to starter solenoid “S” terminal to engage solenoid/starter that is a fairly high current draw.
 

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I was under the impression that you would need to get a new ECU to run with the manual transmission. When I was shopping for a new ECU, there were some models for manual transmission vehicles, and others for the autos. Perhaps you are confusing the computer/they are incompatible. Feel free to correct me if this is incorrect thinking.
 

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I was under the impression that you would need to get a new ECU to run with the manual transmission. When I was shopping for a new ECU, there were some models for manual transmission vehicles, and others for the autos. Perhaps you are confusing the computer/they are incompatible. Feel free to correct me if this is incorrect thinking.
On ’91- ’95 DOHC engines the automatics used same ECU as the manuals, part# only chanced between Fed and Cal spec cars and twin turbo engines. On ’96 – ’99 there was no difference in any of them, except for twin turbo engines. The SOHC engines had different part#’s from DOHC engines but followed same kind of year pattern as the DOHC engines.


Edit: had to add "except for twin turbo engines", so as to not cause confusion.
 

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Yeah you’re right that probably would have made things more clear it’s a 98 dohc sl, the trans that I got came from a 95, I hadn’t heard anything about changing the ecu so it’s still on the same ecu it came with
 

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I'm not familiar with the 3/S auto trans but what I believe the OP is trying to say is that they wired in the park/neutral safety switch and then the car would turn over by the key, not that they connected the wire and it caused the starter relay to turn on. I think OP just worded it poorly. But this makes me wonder if the wiring for the park/neutral safety is basically the same as the clutch safety switch, and if OP wired that up or not.
I’m not the most knowledgeable, so I’m sorry my wording sucks, all I did was basically connect the safety thingy from the auto and boom it starts to turn over but very very badly
 

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I’m not the most knowledgeable, so I’m sorry my wording sucks, all I did was basically connect the safety thingy from the auto and boom it starts to turn over but very very badly
I also plugged in the mat just to see if it would make a difference and it didn’t, I’m currently out rn because we have no power but I’ll get home soon to see if I can explain it better
 

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Yeah you’re right that probably would have made things more clear it’s a 98 dohc sl, the trans that I got came from a 95, I hadn’t heard anything about changing the ecu so it’s still on the same ecu it came with
The ’98 used same ECU for both so that’s not a problem and manual transmission doesn’t care what ECU is in car. Just leave TCU unplugged as there’s no need for it.

......... all I did was basically connect the safety thingy from the auto and boom it starts to turn over but very very badly
Sorry, not enough information here for me to offer any suggestions. I’d need to know like what color wire and it's tracer stripe color you hooked to what point or other wire and it's stripe color. Also I don’t really know what “very very badly” means, I do know there’s a difference in starters for the manual and automatic transmissions and that possibly that could cause starter operation problems if wrong one was now installed.

Edit: Just to be sure that when you say "turns over", does that mean starter turning the engine OR do you mean engine starts but runs poorly?
 

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Flasher
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So you were running it with the MAF unplugged? Why?

Am I getting it correct that you removed the park/neutral safety switch from the automatic transmission and plugged it into the harness on the car? When I did a swap many moons ago, I just jumped the wires together.
 

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So you were running it with the MAF unplugged? Why?

Am I getting it correct that you removed the park/neutral safety switch from the automatic transmission and plugged it into the harness on the car? When I did a swap many moons ago, I just jumped the wires together.
I’m not really sure why but when I plugged it in it made no difference what so ever, yeah that’s exactly what I did it was just a sensor that was on the auto and I plugged in to the harness where it would originally plug in if the auto was still there and it starts, it’s not the starter because I got a starter for a manual. So the starters fine. I’ll try to get some videos if I can. But when I mean turn over it actually starts up and holds revs just very bad it kinda putters out it also revs by itself like it’s trying to stay alive but I’m not sure why. I’m gonna try to start it again when I get power and I’ll take a video and see if that can clear it up
 

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Wait so does connecting that wire to the ECU make the engine start without the ignition being turned or not? As in connect that wire to the ECU and the engine turns over without you actually turning the key? Or will the engine not turn over at all with the key without the wire connected, and when you connect the wire then the engine will turn over with the key?
 

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I’m not really sure why but when I plugged it in it made no difference what so ever, yeah that’s exactly what I did it was just a sensor that was on the auto and I plugged in to the harness where it would originally plug in if the auto was still there and it starts, it’s not the starter because I got a starter for a manual. So the starters fine. I’ll try to get some videos if I can. But when I mean turn over it actually starts up and holds revs just very bad it kinda putters out it also revs by itself like it’s trying to stay alive but I’m not sure why. I’m gonna try to start it again when I get power and I’ll take a video and see if that can clear it up
A video would be helpful to get a better idea about what is going on.

When you say putters out, does the car completely die on you? Another question, you said you got this car and it only had 1 gear cause the tranny was shot. Has the car ever been started before the swap, and did it run well then?

Based on the surging idle and puttering, I would say you either have an air or fuel issue. I would start with air and make sure all the intake bolts are torqued down to factory spec. Pull off the airbox and intake tubing up to the throttle body and go through all the connections to make sure they are snug. Also make sure all of your vacuum lines are connected properly and that your MAF meter is plugged in as well. A bad MAF meter could cause what you are seeing but the symptoms point to a possible vacuum leak.

I recently swapped the motor and put in a new clutch on my 91 Stealth. It’s a SOHC engine, but I had the exact same symptoms when I first started it up with the surging idle and the car dying. My issue wound up being that my dumbass did not properly tighten/torque the main intake bolts, so I had a lot more air entering the vehicle than was supposed to.

You said the car has sat for 6 months too. If you haven't already, I would change the fuel filter. It's a cheap part, pretty straightforward to change (I believe Stealth316 website has a good tutorial on it which I used to do mine) and if you don't know when the last time it was changed, then it is never a bad idea as preventative maintenance; especially if you plan on keeping the car for some time. Taking out, inspecting, and servicing the IAC would be a good next step if these other things I recommended above do not fix your issue.

Last things I thought about would be that the crank angle sensor was moved/is not positioned right impacting your idle speed and how the car is running overall. Also, check your spark plugs and make sure they are not super worn and that the gap is good. If you have a timing light available, you can connect it to each of the spark plug wires to make sure you are getting consistent spark.

Start easy with checking for vacuum leaks and going over the air intake assembly and checking torque on your intake bolts, then check your spark plugs and wires. If these don't solve your issues, you can start heading down the rabbit hole of other possible things it could be.

In regards to the safety switch, I do not have any experience with that, so I will let other more qualified folks weigh in on that. Hope this info helps you out and you get the car running well soon!

- Braden
 

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Wait so does connecting that wire to the ECU make the engine start without the ignition being turned or not? As in connect that wire to the ECU and the engine turns over without you actually turning the key? Or will the engine not turn over at all with the key without the wire connected, and when you connect the wire then the engine will turn over with the key?
Yeah, so if I don’t have that park/neutral sensor from the automatic plugged in it won’t even crank, but with it on it starts to start up
 

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A video would be helpful to get a better idea about what is going on.

When you say putters out, does the car completely die on you? Another question, you said you got this car and it only had 1 gear cause the tranny was shot. Has the car ever been started before the swap, and did it run well then?

Based on the surging idle and puttering, I would say you either have an air or fuel issue. I would start with air and make sure all the intake bolts are torqued down to factory spec. Pull off the airbox and intake tubing up to the throttle body and go through all the connections to make sure they are snug. Also make sure all of your vacuum lines are connected properly and that your MAF meter is plugged in as well. A bad MAF meter could cause what you are seeing but the symptoms point to a possible vacuum leak.

I recently swapped the motor and put in a new clutch on my 91 Stealth. It’s a SOHC engine, but I had the exact same symptoms when I first started it up with the surging idle and the car dying. My issue wound up being that my dumbass did not properly tighten/torque the main intake bolts, so I had a lot more air entering the vehicle than was supposed to.

You said the car has sat for 6 months too. If you haven't already, I would change the fuel filter. It's a cheap part, pretty straightforward to change (I believe Stealth316 website has a good tutorial on it which I used to do mine) and if you don't know when the last time it was changed, then it is never a bad idea as preventative maintenance; especially if you plan on keeping the car for some time. Taking out, inspecting, and servicing the IAC would be a good next step if these other things I recommended above do not fix your issue.

Last things I thought about would be that the crank angle sensor was moved/is not positioned right impacting your idle speed and how the car is running overall. Also, check your spark plugs and make sure they are not super worn and that the gap is good. If you have a timing light available, you can connect it to each of the spark plug wires to make sure you are getting consistent spark.

Start easy with checking for vacuum leaks and going over the air intake assembly and checking torque on your intake bolts, then check your spark plugs and wires. If these don't solve your issues, you can start heading down the rabbit hole of other possible things it could be.

In regards to the safety switch, I do not have any experience with that, so I will let other more qualified folks weigh in on that. Hope this info helps you out and you get the car running well soon!

- Braden
Yeah, I wouldn’t say it completely putters out so I start it and when I hear it start to rev up on its own I just shut it off because I don’t want to cause any damage, we actually did drive it with the bad gears because why not lol. No as to how it ran we aren’t really sure because it in had the one gear and that made it hard to tell but it drove so better than it is now I suppose. Yes I actually did replace the fuel filter, yeah it’s all new plugs and they are gapped. I haven’t taken them out to see if there was gas on them or anything but you can definitely tell it’s cranking the starter when I try to turn it over. I’ll try checking the plenum, I’ll also try to check the crank angle sensor. I just got power back so I’ll try to see if I can get a video in here
 
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