ok guys, i needed to swap out my N370 ECU cause it goes to limp mode due to a bad MOP. replaced the MOP and went to get another ecu. this is a jspec engine on an aspec harness and ecu. i was able to find a N374 jspec and have seen many on this forum just swap it out. i installed it and i can barely start the car and it feels like it's only on one rotor or not sending fuel. i put my "bad" ecu in and it starts and idles great(just goes to fail safe mode)

i searched and found all kinds of info (rumors?) on these ecu's including:

1. just swap it out it's fine......
2. some of the ecu's do that......
3. the jspec is set for different octane.....
4. the jspec has higher fuel cut....
...and so on.

can anybody tell me why it's doing this and what do i need to do to fix it. my car has been down too long and i need it. any help or info is greatly appreciated.

 

anybody wanna help me put this issue to bed?

 

i couldnt tell you whats wrong. i have the same setup. i have a tuned ecu JDM n374 on a ASPEC harness. have you tried to reset the vehicle?

oh one more thing. are you sure its a n374 and not an N3Y4. i put a n3Y4 on my car and it did the same thing. it was really hard to start and when it did, it sounded like **** and ran horribly. make sure you have the proper ecu. thats all i can think of

 

yep, it is definately a N374. reset is no help, the original ecu allows it to start and idle fine. i'm at a loss

 

do you have a friend around who might be able to swap ecus for a minute. i could be that the JSPEC ECU is fried. i'm stumped also. who did you get the ECU from?

 

from a local forum member. took me five days to find somebody here that had one. so no, i don't have anybody i could test with

 

better ask the dude whats really goin on. damn bro. sorry i cant help you out

 

no prob, thanks for the help. i've been messaging with the guy. they seem super knowledgable and sure that the ecu is good. i'm just getting fed up with this problem. i mean damn, i have a nice fast as hell car that i can't do anything with because of a stupid little issue that i can't seem to get around........guess i haven't spent enough $ on it yet

 

wow, a thread about "what battery to use" goes for 4 pages but nobody can help with this issue?

 

are u sure your old ecu is bad, when the s5 omp fails it doesnt allways kill your ecu.

 

replaced MOP with a known-good one and the fail-safe mode still happens. i was informed that it is most likely a bad ecu. i got this ecu just to see if it would help and i don't know why it's acting this way.

 

https://www.rx7club.com/showthread.p...ght=inside+ecu

this is a thread showing an almost identical issue, good responses but no real solutions.

 

well, if the ASPEC ECU will start and idle fine, but throws the code for the OMP, and the JSPEC ECU does almost nothing, that tells you at least that there is something wrong with the JSPEC ECU. N374 should have absolutely no problem running the motor with the ASPEC harness. i say this as living proof. however... if the ASPEC ECU is still throwing the code for the OMP, then, do you think that the OMP you have is bad? i hate to play 20 ?s with you, but is it new or used? OMP will not fry an ECU, its just in limp mode. that should at least tell you something.

 

the know good an tested MOP i put on the car was purchase from Don Marvel at Marvelspeed. i've dealt with him many times, he was a master tech/engine builder for mazda for over 20 years. he and his brother informed me that they have seen a MOP damage an ECU. i tested the MOP per the FSM and it shows to be good. the jspec N374 was from a running car with aspec wire harness before it went to a standalone. i have read other threads about putting the N374 on a car and it having this problem then putting the same ecuon another and it work great...............thus creating my new issue ......why is this happening???
no problem with the 20?'s i appreciate all the help i can get.......the more people offer up suggestions the less likely i am to set fire to this car

 

so, watcha think fella's, buy a new car?, light this one on fire?, buy an entire jspec front clip and swap EVERY part? spend a ton of money i don't have and go standalone?

 

what you are describing is exactly what went through except my problem was the harness itself (we think). i bought the n374 ecu also and it did the same thing as yours, ran like absolute crap. i messed with it for TOO long and after trying several ecus, i spent the money i still dont have and im having my haltech put in this weekend. you say that your still runs good on the aspec then buy another aspec its way cheaper than a standalone system and you already know that it works compared with the jspec. good luck to ya

 

I'm in college station and have a s5 parts car with a working ecu, it's only about a 3 hour drive, lmk if I can help.

 

nightmare, thanks for the info. ima keep tryin to get this fixed hopefully a good aspec N370 will work.

rx7idgit, is it a turbo ECU?

 

Yes it is.

 

well if the mop is good, and at least one of the ecu's is good, then id say you have a harness problem.

 

I swapped in a Jspec motor in my 90 FC and I got 3 N374 ECU that are in great shape and tested good, but when all 3 ecu's are plugged in, motor does not fire. When I plugg in the non-turbo N351 ECU, the motor starts. What's goin on?. please, someone help.

 

the answer to you problem is at the bottom of this thread...

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/jspec-wiring-diagram-pleasee-n374-help-518542/page2/

 

Say *thank you* to Thrasher??? Yes.

So the black box is a knock sensor. How 'bout that.

 

No it's not. The pin-out is completely different.

 

Aw darn. Who to believe? Let's see now. Ennneee meeene meneeee moe...............

This nonsense could be settle with a meter on ohms, one lead on a pin in the black boxes output plug and a little hunting around with the other meter lead.

Series five don't have knock boxes do they???? Only series four? Right or wrong?