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i just bought a jdm turbo 2 swap 1990 vert and i believe the previous owner tried to make the usdm s5 na harness work with the n374 ecu (i believe i need the n370) and all the wiring is a mess if anyone could help me figure out what`s going on it would be a massive help.
I looked into the differences in the US S5 cars years ago. From what I found there is no need to cut anything really so I don't know what the P.O. was doing there. Here are the only diffrences between the two that I posted in this thread years ago. Turbo II Swap w/ Jspec Wiring Harnes - Page 2 - RX7Club.com - Mazda RX7 Forum
Originally Posted by Dak
Took me awhile but here is what I could dechipher from my FSM. This is from my 1989 workshop manual from Mazda.
Differences are as follows:
Pin# 2M on N/A = VDI Control soleniod
Pin# 2M on TII = Knock Sensor.
So I would guess the wire that went to the VDI Solenoid gets connected or extended to connect to the knock sensor.
Pin# 3R on N/A = 6-port induction system(solenoid)
Pin# 3R on TII = Duty solenoid valve(Turbo boost pressure control) From the turbocharger control system section it looks like this is the solenoid that controls the wastegate valve actuator. I would guess same as above for wiring.
Pin# 1U on N/A = AT switch
Pin# 1U on TII = Mileage sensor #2 Don't know what to do about this one.
Pin# 3N on N/A = EC-AT Control(This is an output)
Pin# 3N on TII and MT N/A has no connection.
I would reccomend comparing the FSM pages yourself as well to make sure I haven't overlooked something. Also I'm pretty sure this will not apply to 87-88 cars. Applies to 89-91 cars only.
This may have been covered previously and I didn't search enough( sorry if this is the case) but here goes. So I'd like to do a TII swap eventually. I see complete engines, trans, harness and ecu on ebay all the time. Already knew to not bother with the JDM harness and the motor was prob. only good as a core for rebuilding. What I just discovered last night is the N374ecu doesn't work in a swap most of the time unless you get lucky and get a chipped one, but it does work in USDM factory turbo cars. Most threads on here seem to only talk about/speculate/try to figure out the differences between the N370 and N374 ecu. My thought was what is different in the USDM n/a and turbo cars that would cause the N374 to malfunction. After looking at the ECU pinouts in my FSM here is what I've came up with. If you used your n/a harnes and connected everything in the engine bay correctly why won't it work? I think the problem could lie elsewhere in the car. I've found two pinout differences that aren't in the engine bay. I'll start with the one that's less likely the issue.
Pin 3N on the n/a is an output to the EC-AT control unit. It's not used on the TII.
Now the one that has me curious:
Pin 1U on the n/a is an input connected to the AT switch. It's signal to the ecu is:
A/T Trans = approx. 0V
M/T Trans = approx. 12V
Pin 1U on the turbo is an input from Mileage sensor #2(there is only one on the n/a). It's signal is:
Under 600mi. = approx. 12V
Over 600mi = approx. 0V
Since most swaps are mt cars there will be 12V on this pin. Could it be on the N374 this pin expects 0V but sees 12V and this puts the ecu in some mode that doesn't fire the rear injectors? I read in my searches that there is a speed limiter on the JDM cars. Could this pin be the one used for that? Your trying to start the car but it thinks your going 155kph and shuts fuel and/or spark however they do it. It would make sense if a chipped N374 removes the limiter it may ignore this pin.
Anybody explored this avenue? If it's been tried sorry for the long wasted post. If not it doesn't seem that hard to test. One way since I suspect these sensors live in the instrument cluster( I know the mileage sensors do) would be to swap a TII cluster into a swapped car that has a non working N374. One could also cut the wire to Pin 1U and ground it thus putting it at 0V.
I thought surely someone else has thought of this but if not, maybe I'm onto something.
IIRC those are the only differences between them. So from all that the only thing one may have to do to use a n/a harness in a TII swap is extend or shorten some wires in the engine bay to connect some sensors that are in different locations and cut and ground one wire to disable the speed limiter in the N374 ecu. Your best bet may be to find a good n/a harness and start from there.
My idea is to find a part out with the connections and plugs to ecu so i can place it back together from what i found if i can do that i should be able to start it on the na ecu until i can get a n370
If you're not worried about wire color to replace a couple of hacked wires, one can find a donor harness from something else that uses similar connectors (see junk yard.)
Wires cut at the connector are a non-issue; the ECU harness connectors are surprisingly easy to "de-pin" and repopulate with a new wire and terminals at the connector with basic hand tools.
Edit: last time I was faced with a similar issue, I think I used a neat little tool called a Pin Vice. It looks like a microscopic hand held drill chuck, used most often in crafts and hobbies. I put a large name-brand sewing needle in it backwards (I think it was the kind that is usually ran in a machine.) I was able to carefully push the retaining tabs out of the way without damaging anything, then slide in a new wire and connector.
My idea is to find a part out with the connections and plugs to ecu so i can place it back together from what i found if i can do that i should be able to start it on the na ecu until i can get a n370
Like others mentioned if you can still source new pins there is the re-pin your connector option as your connector looks fine. It almost looks like you can match the wire color at the connector to the cut wire. Though I'm not sure if anyone confirmed that grounding pin 1U works or not in theory it should be all that is needed to get the N374 ECU to work in a n/a car. Apparently the N374 works fine in a factory USDM TII. Also you can't use the n/a ecu for anything more that to possibly start the car and idle. There is nothing in the n/a ecu to deal with boost.
11-22-22, 09:29 PM
