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SOHC Auto to DOHC manual conversion

Hey guys, just registered here but I've been reading posts for a while trying to learn as much as posible.

I was hesitant about asking this here since my car is not a 'VR4' but instead a ff version of the body shell /ubbthreads/images/graemlins/cool.gif

Story is like this,

My car, Auto 4g63 SOHC

Motor sitting in my garage, 4g63 DOHC manual trans. I also have the computer for this motor.

Wreakers just told me $80 for the engine bay harness.

Questions..

When I change my motor/trans and put in the new harness, does the engine harness plug into the computer and the dash harness? or is it one big piece? my gauge cluster is for an auto, will I have trouble connecting the manual harness into the auto dash harness?

Basically is it as simple as ripping the SOHC harness out of the engine bay, replacing it with the DOHC harness and posting it through under the dash and plugging it into the new computer and the original dash harness? or am I in for a nightmare I won't forget?

The car is basically my daily driver so I don't want it down for much time.

I tried looking up under the dash to see if the engine bay and dash harness are one piece, I also took a look at my manuals but still can't quite make out.

Hope this is all clear.

Many thanks

Justin
 
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Perkul8r

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Joined
Oct 19, 2009
Messages
61
Location
Mandan, ND
I have never swapped the harness on a Galant, only cause I have only ever had the VR4. But I know on DSM's its quite a chore to replace the harness. Like pulling the dash and the heater boxes cause the harness runs under it. I know most people that do the swap just ad the wires needed to make the conversion. It seems alot easier.

But I am sure there are other guys on here that have more info.
 

The guy who I bought the motor from cut the computer off the harness with plugs still attached, this was because the car had things like ABS (mine doesn't) and it was for a race car. He was going to make a new harness based on wiring digrams using only the wires he needed to run the motor. Unfortunately I'm not that up with electronics and since mine is a road car, and I want to maintain the use of the factory instrument cluster I think that might be harder /ubbthreads/images/graemlins/frown.gif
 

cspetros

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Port Norfolk, VA
It is definitely a project. I wrecked my '92 Galant GS (automatic) shortly after rebuilding the engine in it. I found a SOHC Galant (base model, no power windows, mirrors, nothing) with a good body but a bad motor. To make a long story short, the engine harness will most definitely have to be swapped. The ignition system is completely different. Also, my GS had power windows, mirrors, etc. In order to make all of this work, the interior harness had to be swapped out. It runs from the ECU (front right), across the dash to the fuse panel (front left), down, and all the way to the trunk of the car. I completely gutted the interior, and swapped everything (dash, seats, carpet, etc) over.

I suggest reading over this entire thread: SOHC to DOHC Swap project

A guy on here a while back wanted to do the same thing, so I helped him with the diagrams and stuff. We spent hours and hours on this. You'll find some good info there. He got his car up and running after the swap, but had some other issues.

Quote:
When I change my motor/trans and put in the new harness, does the engine harness plug into the computer and the dash harness? or is it one big piece? my gauge cluster is for an auto, will I have trouble connecting the manual harness into the auto dash harness?


The dash harness and engine harness are two separate pieces. There are three massive junction connectors directly under the dash on the passenger side. You can see them if you remove the glove box, and look up (it's mounted on the body support that runs across). The gauge cluster will be connected through one of these. The tach won't work due to differences in the ignition system (and, the SOHC tach only reads up to 8000rpm, while the DOHC tach reads to 9000rpm) but the temp gauge, check engine light, etc will. You'll read about all of this in that link I posted above.

You will also need to get an MFI relay for a DOHC engine (located under the dash panel on the passenger side), as the SOHC relay is smaller, and won't connect to the DOHC harness.

Are you swapping in the manual trans too? Do you have the shifter, clutch pedal assembly, master cylinder, etc?

Hope this helps /ubbthreads/images/graemlins/smile.gif
 
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Thanks heaps!

Exactly what I needed to know. I hadn't noticed that my tacho only went to 8000. Luckily I have an MFI relay as the guy had cut the computer out with it attached. I'm changing to a manual at the same time, I have a shifter but not yet the pedals. Not to worried though as I have a quote from the wreaker for $40nzd for all (about $25 usd). Haha you should of seen how confused I looked when I read what sides the fusebox and computer were on, untill I realized you meant left hand drive /ubbthreads/images/graemlins/rofl.gif

I think my Tacho not working would realy annoy me after a while as I've spent a lot of time and money making everything on the car just 'right'. Think I get everything you are saying, if I change my cluster to the DOHC, will that just plug in? or will I end up changing the whole dash harness? if that is the case can the SOHC tacho be wired up to work with the new ignition of the DOHC?

I'm going to have a look with the glove box removed tomorrow, take a look at some more wiring diagrams and also read every word in that link you gave me. If I have any more questions is it ok if I pm you?

Regards, Justin
 

cspetros

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Joined
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Messages
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Port Norfolk, VA
Quote:
if I change my cluster to the DOHC, will that just plug in?



In the manual (the Body/Electrical Volume), on Page 54 of the configuration diagrams is a picture of the junction that I was referring to under the dash (note the connector numbers):


C-09 is a 20 pin connector that contains the wire for the tach signal. It is the same size between all Galant models (The only difference is that some pins aren't used for some models), so it should connect right up without any issues:


I'm pretty sure that the issue is with the SOHC tach assembly itself. It expects a different signal than the DOHC tach does, I think. If you can live without the tach for a while, I would try to find a DOHC gauge panel from someone here on the board. It would work, and you'd have the correct 9000 RPM guage.

Sure, feel free to PM me. I'll do my best to answer your question(s). You might want to post them here though, in case it would help other people. It is the Newbie section, so you can ask most anything /ubbthreads/images/graemlins/cool.gif

 
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Quote: You might want to post them here though, in case it would help other people

Too true, and thanks for all the help. I'm uploading some photos of the car. It was a 88 galant Super Saloon, four wheel disk brakes, all electrics minus aircon /ubbthreads/images/graemlins/smile.gif The motor came from a local guy, complete with computer, mint radiator (with duel fans), starter, two new oil filters, shifter and cables, trans still attached to the motor complete with clutch etc. I seen the car it came from driving around before it was hit in the rear. 160,000kms with new cambelt. The guy I bought it from was going to rally the galant before it was crashed. The guy was a factory rally driver and competed in Europe, Australia and Asia. He was quite a pleasure to talk with.

Like I said I have yet to buy the pedal box and engine wiring harness. I was quoted about $90 usd for the lot. Like the previous guy in the link you gave me I'm also a student (with a family), money's tight so it's going to take me a few weeks to get the parts I need. Then I can make the change. Thankfully nothing on my car needs doing so the initial change (getting it together and running) shouldn't take me more than a couple of days (fingers crossed). Just found a DOHC guage cluster localy for about $25 usd, the wreaker will probably give me the shift boot and piece in the middle of the console that has the over drive button and power mirror control.

Give me a day and I'm sure my little brain will cook up some more confusions lol.

In the meantime here are some pix

This is the car as bought, here the bumper was removed so I could remove the tow bar.








Here is the car at the body shop, windscreen out getting some work done, just surface rust behind the windscreen causing it to lift out /ubbthreads/images/graemlins/ooo.gif and rust around the heater box fixed






 

The car now



Here with it's new bumper, soon to see atleast a JDM rear bumper and posibly sideskirts and garneshes. Then a respray in the origional colour.


And here are the newly installed vr4 2 pot brakes, much larger than the origionals
 

Here is my new motor /ubbthreads/images/graemlins/cool.gif I was sooo exited the day I picked it up /ubbthreads/images/graemlins/tongue.gif




Might be getting ahead of myself but the plan is to eventualy add extractors (headers), 2 1/2" exaust, adjustable cam gears and a small toyota supercharger running low boost
 

cspetros

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Joined
Jul 19, 2008
Messages
512
Location
Port Norfolk, VA
That looks really awesome! Good luck on everything. If you have questions, we'll be here. /ubbthreads/images/graemlins/smile.gif
 

Ok, another question /ubbthreads/images/graemlins/dunno.gif

As you know the car is currently an auto and I will change to manual the same time I change the motor. I tried searching for myself but couldn't find any answers so here goes. the Auto trans computer, is that located behind the radio/console? I took a look in the engine bay and the trans plugs into the current engine harness. So the harness (engine) must be different with an auto and a manual? My reserch has led me to believe the computers are the same with the auto and manual, so does that mean that after the harness enters the firewall from the engine bay it seperates? one way to the engine's computer and another way to the auto trans computer? (and of course to the dash harness etc) or is the trans computer integrated with the dash harness and info is supplied to it via some of those extra pins you mention? /ubbthreads/images/graemlins/confused.gif

Many thanks for the help,

Justin
 

cspetros

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Messages
512
Location
Port Norfolk, VA
The TCU (Trans. Control unit) is located way back up under the radio. If you pull off those plastic sideboards that run along the side, you will be able to see it. It is definitely scrunched back up under there.


Quote:
I took a look in the engine bay and the trans plugs into the current engine harness. So the harness (engine) must be different with an auto and a manual? My reserch has led me to believe the computers are the same with the auto and manual, so does that mean that after the harness enters the firewall from the engine bay it seperates? one way to the engine's computer and another way to the auto trans computer? (and of course to the dash harness etc) or is the trans computer integrated with the dash harness and info is supplied to it via some of those extra pins you mention?



The transmission harness is wrapped into the same protective sheathing as the engine harness inside the engine bay, but once it enters the passenger compartment, it forks. One branch runs to the ECU, and the other branch runs UNDER the rubber matting that's beneath the carpeting, over to the TCU.


As far as the ECU's being different between Auto and Manual models, there is a difference in the fuel maps (I think Keydiver here on the site mentioned it somewhere) but nothing that would be blatantly noticeable when driving.

You can get some really good info on how to do it from this page (it's for a DSM, but essentially the same process): click

If you are entirely replacing the engine harness with a DOHC harness (you should be /ubbthreads/images/graemlins/smile.gif), you can eliminate the TCU harness and TCU completely. The only thing I'm not too sure about is the clutch position switch (if it exists (I think it does, it's just left unused) on the dash wiring harness), but when it is unplugged in manual model cars, the car starts without it (it has a little thing that wears out, so many people on here just unplug it).

Does you car have cruise control (important)?
 
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Thanks very much for all the great info, and for taking the time to edit those images.

No, my car doesn't have cruse control, abs or aircon (if it did I would just remove it anyway /ubbthreads/images/graemlins/wink.gif

I will definately be using a dohc harness. I notice from the link you gave me that the cam angle sensor plug differs between the years. I don't know what year my motor is from (the cam sensor has a long wire from it with a square four pin plug) but I understand that plug is easy to modify regardless. Are there any other major diferences that are likely to put a spanner in the works between the years?
 

cspetros

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Port Norfolk, VA
Other than those mentioned, things should be good. It's a good thing that you don't have cruise, otherwise things would be a bit more complicated. Nothing to worry about there though.

Good luck!
 

A little update, thought I'd add this incase someone else comes along wanting to do an auto to manual conversion. The soundproofing under the dash has a rectangle molded into it, I cut it out (it's already marked) and sure enough behind it in the firewall is the mounting point for the clutch, however only cut through one of the two layers of metal, so it needs to be drilled and cut all the way through. Take a look at the photos.

Here is the piece cut out

And a shot of the new brakes
 

Ok, another question. I've got the money to buy all the parts I need plus have a heap left over so I will be starting the conversion next week. I have the oportunity to buy one of two engine harnesses, a VR4 harness or a standard N/A dohc harness for my motor. The vr4 harness is actualy $5 cheaper than the na harness. Could I use the vr4 harness with the na engine? and just not connect the knock sensor? would the extra wire for the afm not being used matter? I would of course still be using the na ecu. I'm wondering because it would then make it much easyier to go turbo in the future. or is it not that hard to add the wires to the NA harness?

And if that is a bad idea and I just use the standard N/A harness to match my engine can I use my SOHC AFM with the DOHC set-up?

Sorry for all the Noob questions, I'm not that good (yet) with electics. /ubbthreads/images/graemlins/dunno.gif

Cheers, Justin
 

misterfixit

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Aug 4, 2004
Messages
1,596
Location
Midlands, UK
Depends what year as the coil and inition transistor have different wiring on them before/after 89.10

Trans computer is on a bracket under the heater box. pull the centre console and you'll see it underneath. you'll then need to do like you were doing for the clutch behind the trans computer to get the shift cables out. the at select cable takes a completely different route. If you need any loom pics let me know mines coming back from the bodyshop this weekend (sunday/monday and i'll be building it up again.

All the looms are out of the car

Rich
 

cspetros

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Jul 19, 2008
Messages
512
Location
Port Norfolk, VA
Quoting Justin_Cosgrove:
Ok, another question. I've got the money to buy all the parts I need plus have a heap left over so I will be starting the conversion next week. I have the oportunity to buy one of two engine harnesses, a VR4 harness or a standard N/A dohc harness for my motor. The vr4 harness is actualy $5 cheaper than the na harness. Could I use the vr4 harness with the na engine? and just not connect the knock sensor? would the extra wire for the afm not being used matter? I would of course still be using the na ecu. I'm wondering because it would then make it much easyier to go turbo in the future. or is it not that hard to add the wires to the NA harness?

And if that is a bad idea and I just use the standard N/A harness to match my engine can I use my SOHC AFM with the DOHC set-up?

Sorry for all the Noob questions, I'm not that good (yet) with electics. /ubbthreads/images/graemlins/dunno.gif

Cheers, Justin



Hmm. That's a good question. All of the crucial connectors will be present, for sure. If you use a N/A ECU, it will not use the connections that are present for Turbo only models... I'm looking over the diagrams.

The Volume Airflow Sensor connector is the same for non-turbo models (both SOHC and DOHC N/T). The Turbo models have an extra set of wires (as you already noted). If you did use the Turbo harness, you would have to do some custom work with the connector.

Otherwise, as far as I can tell, you would definitely have a loose connector for the knock sensor, and wastegate and fuel pressure solenoid connectors, but everything else would be in order. The catch would be if the DOHC N/T and DOHC Turbo ECU pinouts are slightly different beyond those pins for the unused items mentioned above.

Someone else should also chime in about this. Being a non-turbo Galant owner, that has mainly been my focus, so my turbo model knowledge is not as great.

Are you definitely planning to go the turbo route in the future?
 
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Thanks guys for the replies. CSPetros, to answer your question, yes! 90% sure I will. All the parts are cheap online to convert it, and I know that the cost involved with NA mods and then a ecu that can handle the mods (and get the most out of them) will be way more than adding a turbo, and even running low boost it will put out more power than a tuned NA (I think /ubbthreads/images/graemlins/dunno.gif)

Thanks to you guys and your help (and Andrew B's /ubbthreads/images/graemlins/wink.gif) this conversion is posible.

Cheers, Justin
 

misterfixit

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Messages
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Location
Midlands, UK
I know its been answered already, but heres the TCU next to the drivers foot rest:


Rich
 
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