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Doug, ASE Certified Technician
Category: Transmissions
Satisfied Customers: 8620
Experience:  ASE Certified Diagnostic Technician
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Mitsubishi Eclipse GT: I'm trying to do a transmission swap

Customer Question

I'm trying to do a transmission swap from auto to manual I don't know if I need to swap full wiring harnesses or just the ecu. And if I have to do both then where are they located
Submitted: 2 years ago.
Category: Transmissions
Customer: replied 2 years ago.
And also if I have to reflash the computer
Expert:  Doug replied 2 years ago.
To swap from auto to manual you will need a complete wire harness and ecu. This means the under hood harness AND the dash board harness. You basically will want a complete spare car to get parts from, as the harness does not have any easy splits in it. The primary harness is inside the dash and connects to practically everything, then the engine harness connects at the fuse box and provides the reverse light and speed sensor harness (different on manuals than autos). The dash passes through on the driver side in a few spots including up in the corner near the fender.
Technically speaking you could just swap the transmission/cables/pedals/axles and then hot wire the park position switch so it was always in Park or Neutral and leave it like that... however you will have a constant Service Engine Soon light, constant flashing Neutral light, and you would still have the automatic transmission rev limiter etc.
Realistically.... the only way to go here to do it right is have an entire manual car available to pick parts from. Replace the engine and dash harness, replace the ecu (behind passenger side dash on firewall), replace cluster, replace pedals and cables and so forth. There is no easy nor cheap way to do this.
Customer: replied 2 years ago.
Ok so where does the harness go threw at I can see it run through the bulkhead but I can't find it inside the cat and what about my ignition?
Customer: replied 2 years ago.
And couldn't I just wire my auto ecu by using the unused pins?
Expert:  Doug replied 2 years ago.
The harness goes through in the drivers end of the firewall, up high aimed toward the fender.
You really need to pull the dash out to get a good look at it... and you can't change them out without pulling the dash anyway.
The ignition would have to be swapped if you swap ecus to manual since the key information is stored in there. You would also have to swap the immobilizer ecu under the radio since they are paired. If you have a nearby dealership, alternately you could just have your keys reprogrammed to the new ecu and avoid that though.
No, you could not just use unused pins, it doesn't work like that at all. The two different ecus are exactly that... different. It isn't software that makes them operate differently, they are completely different units, there are no "extra" pins that will make one suddenly become the opposite type of ecu.
The only way you could use the auto ecu would be as I mentioned before leaving the auto harness in and then the park position switch either in park/neutral or hotwired to simulate park/neutral (so that the starter works). This is the wrong way to do things. You will forever have a dozen check engine light codes, the neutral light on the dash will always flash, and you will have no speedometer (manuals use a VSS, 03 automatics use a output shaft speed sensor on the transmission... totally different operation and not able to be "faked").
If you want to do this but want to do it the easy way, that simply doesn't exist, short of selling the car and buying a manual transmission one. It would cheaper that way as well, though less rewarding of course.
If you want the vehicle to be done correctly, you are going to need a donor vehicle to transfer all the parts over, you simply can't cheat and have it be 100% operational.
Customer: replied 2 years ago.
Ok now I just have to take the engine harness or the whole entire car harness?
Expert:  Doug replied 2 years ago.
If you are doing it right... You will need the under hood harness and the dash harness, both are different between auto and manual cars.
Customer: replied 2 years ago.
Ok is there anything I should b worried about besides airbags?
Expert:  Doug replied 2 years ago.
I apologize, there seems to be a problem with the notifications not working on this question, I just happened upon your post by accident.
The air bags are not too much to be concerned over, of course unhook the battery before beginning, and be sure to avoid pinching the wiring on the bags etc.
When you remove the clock spring from the steering column (not necessary, but a good idea to keep from accidentally spinning it), use some tape to lock it in position. If it spins out of position and you reinstall it that way you will break it when you turn the wheel.
Use extreme care when handling the dash... two people would be ideal. These dash boards are SUPER brittle when they get old and break very easily. Having two sets of hands on it will reduce the risk of it flexing under its own weight and breaking into a ton of pieces.
Customer: replied 2 years ago.
Ok I got everything out but the ignition would that be fine? Do I have to reflash the ecu or can I do without reflashING it?
Expert:  Doug replied 2 years ago.
If you do not have the matching ignition key you are still OK with two caveats:
1) You will need to get it to a dealer to program your ignition key to the manual ecu
2) **If it is a 2000 computer you are using** you will need the immobilizer ecu that matches the engine ecu (came from the same car). For year 2000 (and technically early 2001 Spyder) you could not mix and match the engine ecu and immobilizer ecu. 2001.5 and on it doesn't matter if you are getting the key programmed anyway.
If you get the ignition key (And lock cylinder of course), immobilizer ecu and engine ecu as a matching set, then no programming will be necessary.
Customer: replied 2 years ago.
Ok I might sound stupid but what is an immobleizer and where is it located?
Expert:  Doug replied 2 years ago.
No worries.
The immobilizer ecu is part of the security system... it reads the key programming and sends it to the engine ecu. Without a working immobilizer the engine will not be allowed to run.
If you remove the radio surround panel you will find the immobilizer ecu below the radio bolted to the metal frame. There are two boxes down there, the black plastic one, about 3" square is the immobilizer ecu.
If you want to transfer a complete working immobilizer, you need to have the immobilizer ecu, engine ecu, ignition cylinder and ignition key, all as a matched set from a working vehicle to transfer to your car to avoid having to have it programmed.
Customer: replied 2 years ago.
Ok and if I don't have the tumbler I can transfer it and get it reflash ed and I'll b fine
Expert:  Doug replied 2 years ago.
Correct. If you can't get the key/tumbler set, you just tow the car to the dealer and they can program your existing key to the new ecu and you'll be fine.
Customer: replied 2 years ago.
Ok thanks alot that helped out a ton. And will they still program it if I have aftermarket stuff on my car and I swapped trams?
Expert:  Doug replied 2 years ago.
You're welcome.
It should make no difference to them. Honestly you could just tow it up and tell them the key just stopped working and you need it reprogrammed, or that you swapped the ecu and need the key programmed, but not mention that the transmission is swapped etc. They likely wouldn't even notice if you didn't bring it up.
Just make sure all your ducks are lined up before going... if you leave anything unplugged or any other problems, of course that will complicate things and raise a bunch of questions.
The bot***** *****ne though is that it doesn't really matter what you do to it... their job will still be the same which is just to hook up the scan tool, open the immobilizer module in the scan tool, and register the key. Anything outside of that shouldn't concern them anyway.