streettweaked

So here’s the story…. I bought a roller rx7 about a year and a half ago and about 6 months ago I purchased a jdm motor from japan star or something like that. Anyways I noticed the plugs on the wiring harness were different from the regular yellow ones. These are white and bigger/fatter. And the dash harness won’t plug up to the ecu that came with this motor.

Long story short I found out they sent me the wrong year motor and I specifically asked for a 93-95 motor. This one is a series 7 motor out of a 96 or something like that I think and I’m trying to find out what I need to do/ get to make this thing work in my car. Can’t send the motor back cause it’s been too long.

I’ve searched for FOREVER on these forums for clues as to what to do because I didn’t want to ask without looking as so many people tend to do when their answer is so easy to find if they just looked, but it seems weird to me that nobody has done this before or if they have they sure don’t post how to do It because trust me I’ve looked..

This is what I’ve heard so far and some of these ideas conflict with each other so please correct me if I am mistaken and PLEASE PLEASE PLEASE add any info that you have that will point me in the right direction.

First opinion said the short block is the same, but you would have to change out everything else (e.g. manifolds, rats nest, alternator, blah blah blah)

Second one said all you need to do is just need to switch out the harness for a USDM one.

Third one said all you need to do is chop the plug on the JDM harness and splice in a connector from a USDM one. Leave everything else alone.

And I was wondering if maybe I could just keep everything the same on that harness and the ECU, get a 16bit PFC and just get a dash harness from japan…

Please Help Me!! I really want to get past this and move on to bigger and better things!

thewird

iTrader: (8)

Just swap everything from your old motor... Shortblock is the same. It'll take you a days work if your organized. Pic and choose what parts are better for you new motor. You probably don't have to strip it down to shortblock, just enough to get the engine harness out and any other differences.

thewird

Evadrepus

iTrader: (3)

You need a rats nest and a JDM harness. Also the coil mount is different. The hard line from the throttlebody to the thermostat housing is a little different. It is not a big deal.

RogueFab

iTrader: (2)

I agree with thewird, I usually find that junkyard or JDM motors have so many things broken and missing you are best off swapping manifolds, redoing all exterior gaskets, and swapping all the sensors and of course the engine harness.

Tem120

iTrader: (5)

What they said . just swap everything . but since you bought a roller shell lI dont know if you have a harness , and those accesories . it will be a bit more complicated if thats the case. you need ot buy a new harness , new EMS , and swap all that was talked about above . ALSO while hte engine is out , remember to port the wastegate if you plan on staying with the twins .

Reno_NVFD

iTrader: (2)

Sounds like you have quite a bit of work ahead of you, especially if you dont have another motor to get the sensors from. Have you checked the compression of the motor yet? There is a fairly bad rep for JDM motors, it would suck to do all the work to get the motor in and its in need of a rebuild. You can check the compression of the motor with it out of the car. I believe you need a tranny and starter. I would assume if you search for it you could find out how to do it.

Evadrepus

iTrader: (3)

Also do a cooling system leak test because it is just too much work to install a motor with no compression/bad coolant seal.

streettweaked

Thanks to everyone that has responded so far!! And yall are right I don't have a motor to swap anything off of. so let me see if I have it right so far of the things that I need to get.

Rats Nest
Wiring Harness
upper, lower, and exhaust manifolds?
All sensors? ( when you say all do you mean all? or could I keep some of the ones that are already on this JDM motor? does anyone know?)
new throttle body hardline? (What is this? a hose or a wire? or neither? haha)
new ignition coils and coil mount? ( or just the coil mount?)
I already bought a USDM ECU to replace the JDM one. is that the same thing as an EMS?

Question for tem120: why do I need to port the wastegate? sorry if that is a stupid quesiton haha I'm learning as I go kinda.

Reply to Reno NVFD: HAHA yeah I'm starting to realize that I have alot of work and thanks so much for the help! No I have not checked it. when I got the motor, me and my buddy just threw it in thinking we could figure it out but then we ran into problems ( as you can see haha) didn't figure they would send us a bad motor and didn't know they had that reputation of sending people bad motors. as I said above I guess I'm learning as I go along. haha Is there a way to check with it in the car? i haven't hooked up the drivetrain yet.

Does anyone know if there are any parts that the JDM motors have that I could delete that would cut down on cost of buying stuff?
I can register the car in north carolina cause thats where I'm from so they don't need emissions stuff if that cuts down the list of parts that I need.


Again thanks guys for working with me on this and sorry if my questions are a little dumb. I'm new to this whole RX7 thing. but I have always loved this car and now that I have one I really want tot get it going!!

streettweaked

reply to evadrapus: that is a good idea. is there somewhere that tells how to do that and do you know if I can do it with the motor sitting in engine bay not hooked up to anything?

streettweaked

p.s. in that list of parts that I need is there a way to reconfigure the rats nest that I already have to work somehow without getting a new one? or would it be better and easier just to get a USDM one.

Evadrepus

iTrader: (3)

Yes you can do it with the motor in the car. All you're doing is pumping up the cooling system to 35 psi and seeing if it holds pressure. If it doesn't hold pressure, it leaks. Find the leak and fix it.

You don't have a rats nest. You don't need any sensors other than the correct MAP sensor which might be on the car. You are probably better off to buy the coils on the correct bracket than to try to find the bracket alone. Either a JDM or USDM harness will work. OEM ECU is not the best idea. Get a Power FC with a Commander and a Datalogit and save yourself a lot of grief, pain, suffering, agony, suicidal thoughts, despair, etcetera, etcetera. The hardline that is different carries coolant from the TB to the water neck. It is not a big deal to make it work. You do not need intake or exhaust manifolds. Get a set of block off plates. If you have the OEM downpipe get rid of it and get an aftermarket. Get a wideband O2.

I gotta go pick up my bride at the airport. See ya.

scotty305

iTrader: (2)

I put a similar engine in my 1994, but I started with a complete running (with bad coolant seals) USDM setup. Not sure about yours, but the Japanese engine I got had a wiring harness in very good shape but all the pulleys and brackets that aren't made of aluminum had a decent amount of corrosion or rust. Personally, I used nearly all of my original USDM wiring harness and engine accessories because they appeared to be in better shape. It may be possible for some very knowledgeable people to make the JDM wiring harness work, but you need to be realistic about your skills at reading wiring diagrams, crimping new ECU pins onto wires, and knowing that every single one of the connections is correct and won't cause a short circuit or an electrical fire.


If you haven't installed the transmission yet, it's a very good idea to replace the rear main seal, it's very cheap and the old one is very likely to cause an oil leak if the JDM engine sat for a while. I learned this the hard way, after installing the engine and driving a leaky car around for a week or two. If you or your friends are capable, try to replace rear stationary gear o-ring while you have the rear main seal removed because that can leak also. I'm not capable of doing the stationary gear o-ring, but luckily I have a co-worker who is more familiar with rotaries and was willing to help.

At least one of the spark plug wires that came with my JDM engine was bad, luckily I measured them and found one to be out-of-spec before installing them... that may have been difficult to troubleshoot.

streettweaked

What series motor did you get because mine came with big white plugs that don't even resemble the longer yellow plugs on the series 6. I've heard that series 6 jdm motors you can just switch out the wiring harness with a usdm one and a couple of other things and everything will work fine or you could just drop in the motor and the jdm ecu works car as well as long as it's from the same series. that sounds like what your situation was. let me know if i am mistaken.

I've learned by looking at alot of threads on this site that mine situation is a little bit different in the sense that my ecu won't just plug into the car because the plugs are all different and it uses 16bit ecu instead of the 8bit that 92-95's use. (series 6)

and yeah my jdm wiring harness looks great and my pullys don't look terrible but yeah i see what you mean..haha. if i had a motor to swap everything off of i would probably try that, but unfortunately i don't so I have no clue as to what is the same and what is different. the motor came with a tranny so i just slid everything in at once. I'll probably have to take it out to rebuild it sooner or later and I will deffinatly change that seal out. thanks for the heads up.

streettweaked

And I'm no electrician so the whole I'd rather not cut and splice too many wires if i don't have to. haha just sayin.

streettweaked

and evadrepus are you positive? if I get the 16bit power fc for the series 7 won't it not plug up to the car? then I'll be in the same place I am still.. I need to find a way to make this thing plug up to the car and work. remember my motor is a series 7 and the car is a series 6. I'll post a pic of the difference between the ecu's.

Evadrepus

iTrader: (3)

Yes, I'm sure. I bought a JDM just like you with the white plugs. That ECU has 4 receptacles. Two plugs from the engine harness and two from the chassis. So if you attempted to use it and the engine harness, you can't plug it in to the chassis side. So forget that, it is not an option.
I have a JDM harness on my Series 7 JDM right now. Since the Japs drive on the wrong side of the road, the ECU is on the other side of the car so the JDM harness exits the left side of the engine. On a US car, this means the water temperature sender wire is too short. So make it longer. Also the JDM has no EGR and a simpler ACV which you will eliminate anyway (with a block off plate). It sounds complicated I know, but it's really not. If you had the two side by side, you'd see it ain't no big thing.
Get a Power FC for a '93-'95 and either a US or JDM harness for a '93-'95 and those other parts and press on.
I don't need a picture of the ECU's. I have a couple of them in the garage.

Reno_NVFD

iTrader: (2)

Still think you need to focus on the compression amd coolant pressure tests. No point in buying all this stuff, doing all the research, doing all the work and its no good. Once you know motor is good then move on to how to get it to run. Below is a thread about a compression test with motor out of the car. It would be a similar situation for you.

https://www.rx7club.com/new-member-rx-7-technical-256/compression-test-motor-out-car-932248/

https://www.rx7club.com/1st-generation-specific-1979-1985-18/how-inspect-junkyard-engine-365501/

Also the wastegate porting mentioned above helps maintain a stable boost level; search wastegate porting and you'll find out all about it.

streettweaked

ok cool thanks evadrapus that makes me feel alot better about the whole thing knowing it worked out for someone else! haha.

Hey reno thanks for finding those and i will check the compression for sure and the coolant. you are completely right no point in doing all that if i have to get another motor anyways huh? haha. and yeah i was reading about the porting last night and people were saying to make sure you don't boost above 10psi without upgrading ecu and porting the wastegate and stuff like that. so thanks for the tip i never would've known

how can you tell if the motor is not rebuildable? would I have to tear it apart to find out? or if the compression test is bad should i just send it altogether to a shop? I've never rebuilt a rotary before and don't know what the procedures are..maybe i should just wait to start asking these question until after i do the tests huh? haha

ok thanks guys any more info that anyone else has would be greatly appreciated. and thanks to everyone so far!

zkeller

iTrader: (47)

All you need to do with the JDM series 6 wiring harness is move the fuel thermosensor wire to the white connector from the blue connector, change the blue connector by simply repinning it to a US connector, extend the coolant gauge temp sensor wire in the engine bay about 2 feet, and reroute the harness to the opposite side and snake it through the firewall opening. I have done this many times. Everything else is exactly the same, although the JDM cars do not have an EGR switch, AWS solinoid.

I have found most JDM harnesses in much better shape. I assume that the engine bay does not get as hot since JDM cars never had a pre-cat.

Evadrepus

iTrader: (3)

Don't know how I forgot about the fuel thermosensor wire. Also, my car was an automatic so both the blue and white plugs were different.

zkeller

iTrader: (47)

Get ahold of the small recall harness that attaches to the ECU from a manual car and you will have all of the connectors that you need for your conversion. The small recall harness connects the small back box that was added to keep the fans running after the car is shut off when temps are high.

I have successfully repinned auto to manual trans cars without changing the main engine or dash harness. The Mazda Wiring Diagram Manual is a must have.

streettweaked

sorry guys school has been killing me and while i was trying to do the compression test i found out my starter is bad..haha so i'll be throwing that in and testing it tomorrow. sorry for the delay.

streettweaked

and where would i get one of those connectors? straight from mazda? and how much is it?

streettweaked

ok so I finally got a brake from school and was able to do the compression test. I took out the valve stem in the tester that I got from autozone and screwed it into the spark plug hole and turned it over. i'm no professional with these cars ( as you can tell) but it seemed to me that it was hitting quite a bit low numbers. it was hitting 40. I don't know if having the intake manifold off or the intercooloer piping off would affect it and i also don't have one of the oil lines hooked up but i didn't think that would affect the reading. is that normal numbers or do i have a problem? I have a video on youtube if anyone would like to check it out real quick

Front:

Rear:

limepro

iTrader: (2)

needs a rebuild