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st205 into st185 swap faq/ and parts compatibility

Wed Sep 07, 2005 3:36 pm

I have gone through this thread and added a directory for those wanting to do this swap as well as organized some of the information. Keep in mind, do this swap at your own risk. Its been a while since I have done mine so I take no responsibility for things I might not remember. It is still advised to read the whole thread, print it and use it as a bible. This faq is for a swap into a 185. 165s have their own methods and are not covered in this thread. Keep in mind this engine does not have all the emission equipment of the US cars and will likely not pass an emissions test. The engine is also meant for high japanese octane. 93+ is recommended.

This first post has been updated with data from this thread and quoted useful information. This post may not contain 100% of the information you need to do a 205 swap as some questions and posts may have been spread across the forum. If you have questions, continue to ask in this thread, and it would still be helpful to read the whole thread. However I have compiled as much as of the useful stuff from this thread as I could into this single post.

I have put about 1,000 miles on my swap and enjoy it quite a bit. I have also answered a lot of questions about this swap. None of this would be possible without Scott who contributed a lot of information to this thread.

This thread covers the method of using the oem 185 harness to do the swap. The 90-91 & 92-93 wiring is slightly different. I suggest getting an electrical/chassis BGB to do this for your model of 185. Without my BGB, this would had been impossible.
BGBs for the 205 can be found here: http://www.celicatech.com/bgbonline/#6th
This link has 185 and 205 bgbs. One note, these 185 digital BGBs do not compare to the actual book specific to you car year.
You need part numbers, this a great source. http://www.toyodiy.com/parts/

Advice on engine vs clip. I say get the clip. It might be more, but in the end it will pay off. Many of the small things can nickle and dime you, plus you have a starting reference for all the location of everything as well as vacuum. There is almost no proper vacuum reference on the 205, and that is the hardest thing to track down. I spent time talking to people around the world looking at pictures online etc.. to figure out how to sort my setup out.
Also with the clip you tend to get the rear LSD, 205 brakes and body panels. You can sell these items or swap things like the brakes.

The biggest piece of advice in addition to all else in this thread is to get a quality uprated clutch when you do the swap. Its a big job, and you might as well do it while everything is out. Also consider the water pump. A must when you swap your engine is new plugs, wires, dist cap & rotor and of course oil. You should also do the fuel filter at this time while the engine is out. There are guides here how to do it. Just use the oem 185 filter. You might consider doing your downpipe at this time since its easier to get at those turbo bolts.

Below I will collect notes from this thread as well as links to other information.

TIP: Throw nothing away till you are done. You never know when you might need it, even to use it as something else. For example I used my old fuel filter bracket as an intercooler pump bracket.

• You will need to use the 185 radiator. I use the widest ASI radiator since my oem one was aging quite a bit. The 205 one will not fit.

• 205 shifter cables are longer. Might not work.
LechacZ wrote:If ur asking if the rad and shifter cables from 185 car will hook up to 205 motor and tranny then the answer is yes, but rad and cables from 205 will not fit on the 185 car.

• Clutch is the same.

• 185 gearbox will bolt up.

• Use 185 axles. 205 axles are supposed to be longer.

• Hubs can be swapped. This might only be useful when using the 205 rotors since the hub bore is slightly different. You can swap the 205 brakes. Fronts are hard and can be read about here:
Rears are pretty much bolt on, and can be read about here:

• Lower 185 rad hose will work. The 205 upper hose can be used, but needs to be trimmed. Now is an ideal time to install an aftermarket water temp sensor.

• Use 185 Speedo Sensor at gearbox

• Intercooler: If your wta IC did not come with pump and heat exchanger you can use aftermarket options. I used an aftermarket for cobra heat exchanger, and ford racing high flow intercooler water pump. To use the ford pump I had to buy the cobra pigtail as well to wire it in. The other option is going with a FMIC. There is not a lot of weight savings in going to FMIC, but you can build it to support more power for future mods, and you can get to things like the plugs easier. Hoses for a wta IC can be found at industrial hose shops. My home town had a brass fitting and hose shop that could make about anything you needed. If you do fmic you can easily clock the turbo down with a special clip tool craftsman makes. You can find them at sears. You will need to make a bracket for the wastegate though.

• Brackets: You will need to fabricate some bracket. If you keep AC you will need to mount the 205 A/C idle up valve among a few things on the firewall.

• Use 185 motor mounts

• You can use the 185 Power steering pump, or swap the head from the pumps so the fittings will work on the 205 pump.

• Using a patch harness at the ECU will prevent you from having to hack up the oem harness as well as making it simpler to modify things.
Berk makes one as do a few other companies. http://www.berktechnology.com/store/sto ... ectronics/

• If your afraid of wiring you can send off your harness to various places to have them modify it for you.

• Use a power distribution block. You will need this to power the code 54 fix, IC pump, gauge lights, etc... It prevents hacking up your own wiring.

• Make a straight intake. Unless you try and use the HKS mushroom filter, or get a custom k&n filter the 205 piping will likely not fit. If you make an intake go for at least 3". It has been found on the MR2 with 3rd gen swaps that a 4" intake actually produces more power on these cars, so that is something to consider as well.

• Accessory belt from the 185 is about 1" too small. I took it to advance autoparts and they had an identical one in the right size.

• Charcoal canister. If your going to use one, take the one from the 205. If not here is a faq on removal.

• Use 205 igniter

• You do not need to 205 cat sensor in the downpipe.

• The 185 aftermarket downpipe can be used. The turbo is at a slightly different angle though and one of the studs would not be used.

• If you keep the AC use the 185 compressor. The hardlines are different.
Making the AC work is still a work in progress. This thread has some info on it.

• Fan. You might fit the oem fan back in there, but I suggest a spal thin fan. I wired mine in just like the stock one and it operates the same way.

• O2 Sensor: I swapped the plugs from the 185 to 205 so I could use the 205 O2 sensor. Keep in mind this is a very expensive O2 sensor 400+ usd. I bought the recommended Bosch unit, and it caused the car to run richer and get worse MPG. There is a rumor that you can use the 185 sensor but I have not tested it.

• 185 exhaust must be used. 205 exhaust will not work.

• 185 Pump will work for 300hp crank. If your going to turn the boost up on this engine, you need to upgrade the fuel pump.

• Buy a couple sets of cheap copper plugs for troubleshooting. If the car is running rich it will foul plugs easily. No sense if having to prematurely throw away expensive plugs. I went through 3 sets over 500 miles of testing and troubleshooting due to be rich. First set was iridiums.

• Even if you are using the 185 harness you need the 205 harness to cut plugs off of to solder to your 185 harness.

• If you went front mount or did not wire up the 205 pump in the same was as the factory, you will need to resolve code 54.
This thread cover that issue.

Below are quotes for advice on swap:

scothaniel wrote:Use the ST185 harness - MUCH easier. You just move around the wires in the ecu plugs, change the cold-start-injector plug to the manifold air temp, and add an extra temp sensor to the water elbow -unless you dont want the stock water temp gauge or A/C. I have posted a little drawing for which pins to change on the ST185 harness.

For the IC setup, there have been plenty of posts on this subject on the yahoo gt4 forum. If I remember correctly, you use a 2 ohm resistor to fool the ECU into thinking the pump is still there. Cant remember what the IC water level sensor was supposed to see - either a ground or a 12v singal. I have to find out myself, as I'm installing a 205 ECU right now - so I'll have the info in a couple of days.

You'll want to pull the speedo sensor out the the ST185 trans - it'll fit right in.

scothaniel wrote:Sorry for not responding earlier - had a few issues this weekend that kept me busy. I'll PM my phone number, glad to help where ever I can.

The first time I did the swap, I used the 205 harness and tried to swap the 205 fuse box over - big mistake. The bulk of the issues were because I dont have the BGB for the 205, so I dont have all the diagrams for the secondary systems. I spent a lot of hours repinning the dash plugs and working through the fuse box, checking for proper connectivity. It was a mess. I ended up ditching the harness, then later on swapped over just the 205 fuse box in an attempt to free up 2" of space. I need a bigger engine bay!

The second time I used all 185 harnesses only, and re-pinned the 3 connectors for the 205 ECU, then went through the diagrams to make sure all the sensors were getting the proper voltage. Made the changes I listed before and it worked perfectly. So much easier. I made a little diagram that others have used for repinning thiers.

My last 3 harness projects have been more difficult, and have really taught me some valueable lessons - like keeping the wiring as simple as possible. For instance, I spent all weekend troubleshooting some weird s#&% on one harness without any luck. The engine is a 3rd gen 3SGE converted to turbo, the ECU is from a ST205, the harness is from the 3SGE (had to be lengthened and modified) and the car is a 97 Celica ST. I have a major issue with the ECU / ISC valve and troubleshooting has been an absolute nightmare since none of it is stock. A full weeked and the car is no closer to being on the road... very depressing.

When you leave the internals of the harness in tact, its one less thing to worry about, one more thing to rule out when there is a problem.

Just my 2 cents.

We have not found any data that any US 185 came standard with a rear torsen. All the ones we tested when trying to test for a rear lsd were all open. So chances are yours is too. You can use this thread to determine if yours is, which makes swapping the rear 205 pumpkin in an easy solution. All rear diffs are the same ratios for alltracs/gtfours.

CMS-GT4 wrote:So I just finished doing my notes for a 92-93 pin conversion to the 3rd gen, and all I can say is wow. It looks like I may only have to move 2 pins. FPR (Fuel Pump relay) and PIM Turbo Pressure sensor.

Everything else matches up.

All I have to switch after is the install is a couple of wires for sensors on the engine end, and it should be good to go.

Now I just got to make sure I have the info figured out for the code 54 intercooler pump since I will have a fmic.

Here is a link to the 90-91 pin swap to 205.

http://img440.imageshack.us/img440/154/ ... mod1rz.jpg

k_trac wrote:Ya, motor mounts dont match up....its too bad, I had them on when I was first putting the motor in then after a little tweaking I realized that only the half of the rear mount was compatable.

I did use my gen3 power steering pump however, it just had a different outlet for the high pressure line, which was a little tricky to work on in the car, but i got it all together.

I think I am going to stick with the 205 harness, the whole this is legnthened now, so I just gotta match up the box, may have some time soon. :shrug:

Let me know how its going man!

CMS-GT4 wrote:Please do.

I think I have all the wiring sorted out less the two water temp sensors on the elbow.

In the place the THAM sensor will go, I have an egr temp sensor. I am just going to splice it to the THAM sensor.

The rest should be cake. Except those hoses...

k_trac wrote:*UPDATED*

Ok, so I am soldering in 205 plugs to the 185 harness where needed-
-O2 sensor
-Had to gind some material off the 205 ignitor to fit into the 185 plug, went on, but barely, may need to swap the plug over if it acts up
-Knock sensor
-Oil pressure

I have the whole 185 harness in place, 95% plugged in....

Things I have left-
-Pin swap
-Wire up IC

-Is the 185 injector resistor / fuel pump resistor ok to use?
-What plugs into that green vsv looking plug on the 205 charcoal canister?
-How do I hook up the temp probe in the downpipe?

Josh or scott... :shrug:
Thanks mang

k_trac wrote:I do have some tips....there were a few wierd things I ran into along the way. Most of them wont apply to you Josh, since you have a 92 and arent running the IC. ex- wiring schematic had wrong colors listed for some IC wires.

I did figure out how to pull the pins, requires very little force, and a VERY small pic. Actually, I think a sewing needle would have worked best. I could draw a picture of what it looks like inside now that I understand it.

Im sure Ill think of other stuff.

k_trac wrote:Few things about the pins-

Ill take a pic of the pins later today. Dont mar up the plastic, its easy to do. It takes very little effort to pull out he pins, so if you are forcing it, youre not doing it right.

Another thing about the pins- There are two different sizes. if you look at the face of the 13pin connector the outer two pins on eash side have bigger holes, differnt from all the others.

So if you do have to swap those pins on your 92, you have to cut off the pins and use the small or big type depending on which way you go. I salvaged some small ones from the AC harness of my 205 harness. Still had to modify those with a dremel to snap in fully.

As for the water temp, Ill check that again and let you know which wires I used. One of the two codes im getting is for a water sensor. The other is the temp sensor in the air cleaner. So I have to look into those, but besides that, everything seems hunky dory!

k_trac wrote:Here is a pic of my pick, deppining the harness. If you have a white connector of some harness, like the small AC plug that goes behind the glove box, take a look at it.

When you look inside one of the pin holes that does NOT have a pin, you will see the little snap that holds the pin in place.

I say look at a white connector because you can actually see inside bc its a lot lighter. Once you can identify the snap that holds the pin in place, try moving it around with the pic. All you really need to do is push it upwards, away from the pin.

What I noticed is that it does not work well to just wedge the pic in between the snap and the pin becuase it binds up that way. Take the time to push up without touching the pin and pull the wire out the backside.

You really do need three hands, one to hold the harness, one for the pic, and one to pull the wire. I used my chin to hold the pic in place most of the time. You will create your own method. A vice for the harness would work too.

On an aside, my CEL stopped coming on, took it for a hell ride around the block....YES, A LOT FASTER THAN A STOCK 185!

Still dont have temp probe or charcoal canister hooked up to anything.....



CMS-GT4 wrote:Made some progress today.

Changed connectors for
-O2 sensor

Also changed out the head on the A/C unit.

I need to see pics of the water neck and how others did it.

Edit: Dug through the 205 bgb and found the THAM.

CMS-GT4 wrote:Just an update, I am getting close to done and being able to start the car up.

I have a question though, can someone tell me where this water line connects to?


k_trac wrote:That looks more like the spot for one of the water temp sensors. I dont know which one, but theres only two.

As for the AC sensor in the water elbow, you need to pull off the sensor from the other elbow and find out what thread it is. Im pretty sure that its a straight thread that seals on a copper washer. So you would need to drill, tap, then get a flat sufrace to seal against. Pipe threads are easy, they just seal themselves.

Dude, for the belts, I would think they are the same as gen2. I used a alt. belt from a non AC 5sfte engine with a modified tensioner. I would bet $20 that the belts that came off your gen2 will fit the gen3.

YES, it does matter which wires go the the THAM etc. Just match the + to+ and the - to - :D

You will need to swap of the connectors for tham and tha from your st205 harness. You keep the st205 sensors, and splice the connectors into the 185 harness....actually the 185 may fit....try it out.

Its the sender for the temp gauge on the dash.

scothaniel wrote:Wow, this thread started in back Sept 05. I feel for you Coldiron, you've been working on this project for almost 2 years now - I'm sure you've got to be pretty frustrated.

The 205 injector coil pack has the same resistance as the 185, the only difference is the pigtail. The 205 fuel pump resistor is also the same.

Your vac does sound low. I'm usually idling in the mid-20s, with vacuum overrun around 30hg.

CMS-GT4 wrote:My swap, pretty much finished.

Here is the thread where I am trying to figure out he AC.

CMS-GT4 wrote:No time to summarize, but you may get questions answered now and then.
TO swap the alternator, just change the plug on the harness. Remove the 185 plug, and solder the st205 plug. This is what you will be doing for all the items that require a new plug.

I know its a lot, but I suggest reading the whole thread, and take pics and notes of all your vacuum lines on the 205 engine. It would also be wise to post your pics and progress here as it will help some help you if you have an issue, and it also add to the data of what one has to do to do the swap.

CMS-GT4 wrote:
aus jd 2703 wrote:Hey has any one figured out a way to wire the ecu and intercooler up so it doesn't throw a code at all

It requires all the 205 connectors. There is something special how the 205 plug is wired to make it work. So if you have a 205 clip, you can pull the wires and make it work, if not you are best doing the code 54 fix.

aus jd 2703 wrote:Also I have an early 1990 3sgte so I don't have te1 and te2 what did u guys do here?

On my notes those are listed as "check connectors." Its been a few years so I do not remember what that means.

Now on the 1990 BGB it looks like the te1 is listed. It is just marked as T but the description is t-e1.
I am not sure about te2 though. You may want to do some research and find out if it is somehow related to OX. Some people in this thread did this on a 90-91 model, so you may want to PM them and post your findings here.

http://www.celicatech.com/imagearchive/ ... /FI/FI.htm

Direct link:
http://www.celicatech.com/imagearchive/ ... I/FI95.htm

KORacing wrote:just completed this conversion on a 90 alltrac thanks in big part to this thread. I came up with a slightly modified fix for the code 54 that didn't use a bulb, but two 1/4 watt 10k resistors in parallel (equals 1/2 watt 5k ohm load). On the intake temp sensor, at the AFM connection I put a 10k resistor across the THA and E2 pins and code 24 went away. Thanks for the great info. Would be nice to see this information in a more concise format -- I may use the information here to create an article on the swap.

BTW, I used the 90 4 wire o2 sensor with the 90 engine harness just fine.

Cost to do this conversion again (not including parts): $2200

On this customer car we also installed a front mount IC setup with custom pipe, painted and installed a CS front bumper, and installed a Street Brawler billet 58mm turbo kit (gen 3 of course), custom air intake with the battery still in stock location, and a Blitz spec R boost controller.

KORacing wrote:
CMS-GT4 wrote:Glad it helped. I might condense it some day whenever I finally finish my car.

EDIT: Maybe you might help me. I notice a slight dip in idle when I hit the gas. Any idea what to check for? Everything is stock but the intake, and turbo back exhaust.

If your TPS adjustment is correct, then I'd say that it's likely that it's running a little rich or lean right at throttle tip-in causing a slight hesitation. Could be due to a incorrectly reading temp sensor (air or water), o2 sensor, etc. Hard to say what it is if you are running all the used JDM parts. Fuel pressure correct? Not a lot of info from the stock ECU...

I actually started the car we swapped with a Hydra to see what the temp sensors were reading to see if things looked normal before starting it with the stock Gen 3 ecu, but not really an option for most people...

KORacing wrote:
aus jd 2703 wrote:Won't not running a tha sensor throw the ecu offas it's a VE based map? I'm looking forward to putting mine on the road just gottamake a custom intake hose and water lines for the wta ic

The THA is probably much less critical to running than the THAM (manifold air temp sensor) as that is the sensor used primarily in the speed density calculation. My guess is the THA is used as a correction for ambient conditions as it is pre-charge cooler temperature and ultimately, it is the temperature of the air in the manifold (post charge-cooler) that is critical to how dense the air going into the engine is.

• Info on Speed Cut
83841 wrote:HKS SLD ( speed limit defencer defender )
http://www.rhdjapan.com/hks-sld-speed-l ... ype-i-9835

Found this on GT4OC for you if your running stock JDM ST205 ECU

ECU will have 3 plugs. What you need are:

Big Brown Wire (Earth)
Black/Yellow Wire (12 Ignition Power)
Orange Wire (Speed Signal to ECU)

Check an ECU pinout diagram if you're not too sure where those are but they're all unique from what I can remember and pretty easy to find imo.

Make sure you have a decent set of crimps or needle nose pliers as the bullet crimps supplied aren't the best for the size of wire you'll be crimping, ended up soldering mine.

Black Wire on SLD -> Brown Wire
Red Wire on SLD -> Black-Yellow Wire
White Wire on SLD -> Orange Wire Loom Side
Yellow Wire on SLD -> Orange Wire ECU Side

There may also be a blue wire on the SLD but this is not used from what I can tell. Instructions are only guaranteed for ST205's and not other GT4s as I can't honestly say everything will be the same, I would imagine they are but without having wired one up in one I can't say for certain. SLD also tucks away nicely under the little L-Bracket thing under the ECU that the carpet velcro's onto. Works a treat as far as I can tell. Hopefully this information will help someone.
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Last edited by CMS-GT4 on Thu Mar 14, 2013 11:22 pm, edited 17 times in total.

Re: st205 st185 parts compatibility

Thu Sep 08, 2005 7:51 pm

Radiator - no, they are different

Pressure plate - fairly sure they are the same

shifter cables - I had a ST205 box fitted into my ST185 without changing the shifter cables, so I'd think yes at the gearbox end - but the shifter could have a different connection - don't know

Thu Sep 08, 2005 10:04 pm

rad - no
pressure plate - pretty sure it wiil fit - 185 has same clutch
shifter cables looked different on the 205 front cut i had

Wed Sep 21, 2005 2:00 am

I used the 185 cables on my 205 tranny, no prob

Wed Sep 21, 2005 1:24 pm

Weird, I thought I kept the 185 rad.

Wed Sep 21, 2005 2:36 pm

Maybe you did. It seems they are different, but it may require a hose with a different bend to use. I will have a better idea once I start puting my car together.

Wed Sep 21, 2005 3:04 pm

JC, i thought u were asking if the componenets are similar to each other...
If ur asking if the rad and shifter cables from 185 car will hook up to 205 motor and tranny then the answer is yes, but rad and cables from 205 will not fit on the 185 car.

Wed Sep 21, 2005 3:27 pm

OK. So I can use my 185 radiator? And I still am using a 185 box, so I just need to get new 185 cables.

Wed Sep 21, 2005 5:56 pm

Did anyone here do their own wiring? Did the harness have to be extended? Mine is cut, and I am hoping that I will b e able to match up the wires easily. I hope...

Wed Sep 21, 2005 6:43 pm

Yes, you have to extend the ecu harness, 80 wires in all that need to be cut and have roughly 26" added to make it to the hole.

I am half way done with that, hopefully do a little more tonight....

Next, the only thing that I have left is the fuse box mating....not sure what EXACTLY needs to happen, but I got a pretty good idea...after that, I should pretty much be able to turn the key, besides a few little details....

Let me know how its going, and if you need any help, drop me a line.

Wed Sep 21, 2005 6:53 pm

Can you PM me your phone number? We can keep in contact with each other progress. Maybe we can throw some sort of write up together once we are done.

I plan on taking pics of the progress.

Are the wires easy to match? Also, are you using the wta IC? I am not, and having to use a fmic. I hear if I ground the wire for the wta cpu, I won't get an error code.

Thu Sep 29, 2005 3:56 pm

Here are the problems I am running into.

• Any sugestions on how to avoid error codes from the IC, IC ecu not being present?

• Can I use the 205 fuse box, and tap my main body harness into that, or do I need to have the ecu tap into the 185 fuse box?

• Do I need to modify the speedo electical since I am using a 185 gearbox and the gear speed sensor?

Thu Sep 29, 2005 8:03 pm

Use the ST185 harness - MUCH easier. You just move around the wires in the ecu plugs, change the cold-start-injector plug to the manifold air temp, and add an extra temp sensor to the water elbow -unless you dont want the stock water temp gauge or A/C. I have posted a little drawing for which pins to change on the ST185 harness.

For the IC setup, there have been plenty of posts on this subject on the yahoo gt4 forum. If I remember correctly, you use a 2 ohm resistor to fool the ECU into thinking the pump is still there. Cant remember what the IC water level sensor was supposed to see - either a ground or a 12v singal. I have to find out myself, as I'm installing a 205 ECU right now - so I'll have the info in a couple of days.

You'll want to pull the speedo sensor out the the ST185 trans - it'll fit right in.

Thu Sep 29, 2005 9:08 pm

Let me get this right. I just take the harness from the 185 fuse box, and run it to the 185 ecu and change the pins to match the 205 pin out?

That sounds really easy, if that is what you are saying.

Thu Sep 29, 2005 11:12 pm

it's easy, but tedious.
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