1990TurboII-75K

Has anyone done a detailed photo and feature list of what is exactly the same and what is different about the US N370 and the Japan N374 ECUs?

I have read where peaople have successfully and unsucessfully used them for their cars. The differences mentioned were varied from nothing to injectors not working. I have heard that the CEL light is not driven on the N374. The N374 has an additional black box on its right side - for knock sensor circuitry or something else. You have to chip (replace the program memory) a N374 to make it work in an US car.

It would be nice to know exactly what the differencss are and are not.

Does anyone have detailed high resolution internal pictures of the PCBs?

Would anyone have a "dead" N370 or N374 for dissection purposes?

1990TurboII-75K

Isn't there any interest in this topic? This would eliminate alot of confusion and pain for everyone.

Does anyone have any confirmed experiences with these two ECU's?

This is my N370 ECU PCBs from a 1990 TurboII.

RotaryResurrection

iTrader: (8)

Some of the recent speculation got me to thinking.

Everytime I have plugged a non-modified n374 in and had it work properly, it has been on a genuine USDM s5 turbo, not an NA converted to turbo. I once had a stack of n374s that I tested in succession on a running USDM s5 turbo car with no change in driveability whatsoever.

I also once had an NA to turbo convertible swap, and it too ran an n374 without issue. However the n374 was a knightsport chipped model, removing rev limit, boost cut, adding fuel, etc.

Then once I did a turbo conversion on a customer NA car and the n374 (stock) would not fire the rear primary. I wound up giving him a credit toward his bill, and I believe he found an n370 and that of course cured the problem.

So, it would seem to be:

-non chipped or chipped 374's can be used in USDM s5 turbo II's
-non chipped n374's can not be used in USDM s5 NA's converted to turbo, but chipped ones can be
-n370's can work in any USDM s5 car running a turbo engine
-

1990TurboII-75K

So, it seems as though the stock USDM TurboII car will run with a stock N374.

The next question is what are the differences between the two ECUs. In other words, are the I/O pin outs exactly the same. I have heard (but never seen) that there are wiring diagrams for the Japanese car. Does anyone have one OR a list of the I/O pins and functions?

The reason I'm asking is because when comparing the N374 photos with those of the N370 there are electrical components that are missing or installed depending on which PCB your using for the reference.

This makes me think that if components aren't there then that feature can not be there either. Is the missing feature emission related? CEL display? I don't know.

Can anyone take better N374 photos? These were from the internet and are low resolution and not very clear. What's that black box on the side for? Knock detection?

N374 with Black Box


N374 Analog I/O PCB


N374 Digital PCB

arghx

iTrader: (3)

I thought that the "black box mystery" remains unsolved.

1990TurboII-75K

One thing that I have noticed from the photos is that the silk screened PCB numbers for both of the ECUs are the Same => 079721-2283.

This would indicate that the circuitry function would also be the same if all the same electrical components were installed for each board.

Some of these differences may also be within the PROM software chip. This programming would probably be different for the US and and Japan car markets.

The differences between the ECUs driveability may be subtle or not perceptible depending on the cars options or wiring harness used. I'm assuming things are STOCK so that FSM wiring diagrams apply.

Anyone have confirmed observations to add?

1991rx7vert

Well then guys I'm screwed before I even started...I'm about t do a N/A to TII swap and I already got the N374 off ebay for $134.00...does this mean my swap won't work?? I can't seem to find a USDM TII ECU.....This sucks

1990TurboII-75K

Others with more experience may have a definite opinion based on their experiences (as previously mentioned). I really don't know.

That's what this thread is about - trying to find out exactly what is different between the N370 and N374 and how to use these parts correctly.

The Griffin

IIRC the japanese ecu's have a "speed cut/ limiter" function(180km/h), and the black box's defeat that function on "re-chipped" N374's. I don't recall seeing those on regular N374's, maybe someone can confirm that?

1990TurboII-75K

What's IIRC stand for? By "re-chipped" N374 do you mean the previously mentioned KnightSport chip or some other? I have seen this REDOM chip also.

87 t-66

iTrader: (133)

that's false, ALL of the jdm n374 ecu's have that box from the factory (at least the 100 or so that ive seen). i still dont think anyone has a definitive answer on what the black box does. there is a screw on the back of the jdm cluster that i believe removes the speed limiter

1990TurboII-75K

Does the N374 "black box" in any way connect directly to the ECU's I/O pins? Does it connect to some harness other than the USDM Turbo II stock harness? Who has experience connecting to one of these "black boxes"? Or does everyone just leave it hanging there connected to nothing?

Wh1t3 C0m3t

right on both counts. i remember seeing a japanese write up on how to remove the screw to cancel the speed limiter

JustJeff

iTrader: (13)

1990TurboII-75k

You can still have my N/A ECU if that will help you out? But I'd like to keep my N370 in case I can repair it somewhere down the road.

1990TurboII-75K

What I'm trying to do here is to definitively document the internal PCB/Software/electrical component differences between the ECU's. Then hopefully account for problems with various applications in cars.

One thing I would like to try is photograph both ECU's PCB boards at high resolution with and without components on the board. Then overlay the photos to give an "x-ray type" of combined photo to inspect and be able to trace all the signals from the I/O connector. This would tell us what I/O go to what PCB components and what I/O pins go to components that are not installed or missing for each N370 or N374 ECU.

Does this make sense? It is very difficult to follow the copper traces with all the components installed on the PCB, therefore I need "bad" ECUs (with good traces - not charred) to completely disassemble and photograph the bare PCBs.

eriksseven

iTrader: (6)

IIRC = If I recall correctly

1990TurboII-75K

ISHK = I Should Have Known

One internal difference between these ECUs must be the software (more correctly=firmware) in the EPROM chip. This contains the program that runs the engine and all the output devices based on internal tables and what the input sensors are reading. If there are hardware differences between the ECUs then the strategies must be different. Inaddition the US vs Japan markets probably have differnet drive styles and government regulations that may require other differences between the ECUs.

The table below is the start of a log for confirmed Firmware chips that could be in either ECU. If anyone has additions that they are aware of - please, post them here.


N370 vs N374 ECU Firmware Comparison Table
-----------------------------------------------------------

ECU___IC660 EPROM chip P/N___Model/Year
===============================
N370___079753-1053____________USDM 1990 Turbo II Coupe (Stock)
N370___079753-1064____________Unknown (from photo on internet)
N370___REDOM (after market)____Unknown

N374___??????-????______________JDM ???? Turbo II Coupe
N374___KnightSport (after market)__Unknown

Also, see this link (https://www.rx7club.com/showthread.php?t=729017) for parts I'm trying to locate for this study.

Sorry, I can't seem to make a very nice table without spaces included.

1990TurboII-75K

These are photos of an ECU supplied by "Member: chibikougan". Thanks again for the help. This is the first of (2) N374s for dissection and inspecting. More photos to post soon.

Sample #1 - N374 Analog I/O PCB (Comp Side)


Sample #1 - N374 Digital PCB (Comp Side)

The Griffin

You've seen alot of N374 ecu's then. All in person or a couple of pictures 50x each? Just kidding! So what does the little black box do then, or should I ask how does the 180 km/h cut work? Is it a fuel or ignition cut? That little screw is just a way to defeat it by the sounds of it, doesn't tell us anything about where the input is to the ecu...curious

1990TurboII-75K

One of the reasons for looking at the N370 and N374 ECUs is to determine where they are are the same and different. Right now, I would like to limit the investigation to the I/O pins between the 2 ECUs and the functions within the case.

However, the little black box seems to be another part of the story. If anyone knows how it is electrically connected to the N374 - in other words what pins of the ECU does it connect to? That may be helpful?

NaturalSmooth

iTrader: (6)

The little black box is for ABS. at least thats what i was told.

NaturalSmooth

iTrader: (6)

only jdm fc's had ABS. so there is no wire harness for the US to plug into.

Napsterfreak15

/\My JDM harness plugged into that black box on the ECU.. I can probably take some pics of it if you want me too.

I've had numerous N374 Ecus and I could never get my injectors to work so i went stand alone.

And my set up was a true Jdm set up too. The only thing that was USDM was my rear harness.

Before I did that though I brought my car to the dealership to read the codes in the ECU. All the Info came up in Japanese so they couldn't do anything for me lol

walken

iTrader: (6)

ABS was an option on the s4. standard on all US s5 coupes.

Hecubus84

iTrader: (1)

Actually, ABS was only standard on S5 turbos.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/specifications-what-did-2nd-generation-rx-7-come-w-options-standard-features-642372/