ok there are no s5 gurus to help me figure out how to get a 374 jspec ecu into a 91 gtu n/a chassis (been asking for days) so i need a wire diagram for a jspec car.sounds easy but when i go to .ja website all they have is n/a diagrams also. so they say just buy a n333 ecu and be done with it -----not likely. been looking for days also even the local ecu rebuilder can't find one under $300 ($150 is fair). i'm one step from pinning out the entire jspec BODY harness for the engine harness pins out ok to n/a diagrams. the problem i'm having is the n351 runs fine but the n374 ecu wont fire the rear injector(primary) the ecu is good because we ran it in the front clip we bought. we are using the n/a nonturbo harness with pins 3d 2k and 1r disconnected per HAILERS recomendations. i see many posts on this same topic with the 374 ecu so there has to be a logical answer

 

Are you running an S5 TII motor in the car?
if yes, check it out. -(if no, then I don't know what the heck you're doing)

I just finished a full S5 Jspec TII swap on my 90 GTU.
& I'm still using the S5 N/A wire harness.
I first tried an N374 ECU, because It was all I could find at the time, & the guru's said it would work..
Well, it didn't work for me!..

The N374 would plug in to the harness like normal,
But the car ran like complete ****..
it flooded out the back rotar really bad, & I couldn't get the timing right.
'Sounded like it was running on one rotar or something..

After a way too much time spent trying to figure out what the hell was wrong,..
I finally ditched the N374 & hooked up an N370 ecu,..
It runs great now.


-Chris

 

The ECU should fire the injectors fine... I would be led to believe there's a problem with the harness or wiring in general... What injectors are you running? If you're running anything but the stock high imp. 550's you need a resistor box... Just throwing a few ideas out there... I would start by getting an N370 harness to work with...

 

The S5 N/A harness works fine with the N370 ECU. It plugs right in..
If you wan't the knock sensor, hook that wire up to (I think its the 6 port solenoid plug, can't remember, its been a while) search to confirm this,.. its the same pin on the ECU.

Some people also need to lenghthen their TPS plug wires, but I didn't have to.

My N/A harness is in good shape, & my wiring correct.
It was the N374 that was the problem.
To confirm this, We tried it in my friend's S5 TII & it caused the same problems as in my car.
I suppose It could have been a bad ECU, but I have heard of other people having this same problem.

See if you can borrow an N370 from a freind & try that out.

 

i would just try to find the N370. i am just as frustrated as i am having precisely the same issue. the N374 i have werks fine in another car with aspec harness but not with mine. i would LOVE to have a board schematic for this friggin ECU.

good luck

 

He's running a S5 TII engine...

 

doh, that's why i edited

 

ok it's a 89 gtu-s5 with a jspec 90 t11 motor s5 also. the overall responce is the 374 ecu IS different but why? i think its the body plug that is the problem so i'm looking for a jspec body harness diagram. everything is stock jspec t11 (injectors,air flow meter,boost sensor).the n374 should have a more aggressive map in it--aka more power if i wanted a aspec i could have bought it cheaper.thanks for the input keep it comming we'll find an answer soon i hope

 

The only difference between N370 and N374 is emissions related...

 

I've used N374 in many us-spec cars without any problems.

 

I wonder why it works for some & not others.
My N374 was from a TII with an Automatic, would that make a difference?

 

The S5 USDM and JDM ones are the same the only ones that can differ and not always is in the S4 because of Mazda mix matching the CAS sensor. There is no fuel map on the FC ECU and no one offers bettor performance unless you count the N338 not needing a FCD.

 

ditto

 

was that in NA/TII swaps, TII's, or both?

 

s5 NA using NA harness with N374 ECU
s5 vert using turbo harness and N374 ECU
- several others which I cant really recall.

 

hmm the plot thickens. let me add one other small detail with the 374 i get fuel pump constant with key on and the 351 wont come on unless i jump the yellow connector, but when it starts i can remove the jumper and it runs fine (the truth wiil come out just ask the right questions lol) i 'm NOT using the jspec resistor for the fuel pump.

 

Various assortments, in stock TII's as replacements, in conversions using n/a harness and TII harness, etc.

 

sadly the reports stoped comming in, and all the troops were lost. the war was over, there were no real gurus left, only vauge help. so our warrior walks back into the garage with a lonely test meter in one hand and a greasy diagram in the other wanting to find a simple shorted wire or some other screw up so the gurus didn't die in vain.

i'll report any findings
thanks

 

one thought. after doing ALOT of reading, most 374 probs are flooding one rotor. i read a post where it said one end of the injector harness (two clips at the same place)are for primary and secondary for the one rotor and the other is for primary and secondary of the other rotor ----hmm i thought it was primarys on one end and secondarys on the other. this should be true for a n/a nonturbo harness but just but it may not be true for the jspec pinout (bolth injectors firing on one rotor = flooding or no fuel to second rotor) hmm! something to check. maybe this is why the 351 ecu works fine. too bad you can't use noid lights on these engines. i thought i tested them at the ecu with a test light

 

Let’s try this again. JDM and USDM are the same. You have one P and one S on each lead they are not paired on any FC no matter the origin. The lead with the O2 sensor on it is the Rear rotor the longer lead on each of the harness is for the S injector.

 

ok so the pair under the lower intake and under the vacum lines with the ground lug on it is front rotor p and s and the pair with the o2 sensor lead near it is the rear rotor p and s ( forgive me im using a nonturbo harness and they wont reach) i'll get pics to clarify soon

 

pics giving me a hard time, but the lead with the ground and temp sensors has a clip with white tape on it which is PRIMARY front (lg) and the other clip is PRIMARY rear(lg/b). the lead next to the o2 sensor and tps has a shorter clip with white tape and is SECONDARY front (lg/w)and the longer is SECONDARY rear(lg/r) exactly as written in the fsm. no guess work here. the car runs fine on the stock 351ecu so i have a bad ecu i guess, but it worked fine before the r&r i did nothing but unplug it store it and reinstall. this is not over so forgive me if your bored with this thread------ still no 370 ecu available that i can find at a fair price

ps: this is a 89gtu-s that's black i read there only 20 built in 1990 how many were built in 89?

 

Geezuschrist, your N374 ECU is *FUCKED*.
Is that the straight answer you're looking for?

I've messed with N374 ECU's, and they work identically as US-Spec N370.
I think someone already said that.

Can you put two and two together now?

Your N374 most likely came from a JUNKYARD.
The cars get treated like dirt...literally.
I put money your N374 ECU is BAD, or more accurately...your rear rotor injector driver is FUCKED.


-Ted

 

car running nice on n351 still looking for ecu lol

 

$10k grand prize winner i am. i fixed it for all those that have a bad n374 ecu heres the fix for $25 www.mts.net/~chipsale and buy the aftermarket knight sport chip. the installl was easy(with the right tools) and came complete with socket. the car runs beautiful. i wish i knew what happened to the eeprom that was in it ,but it works now. just in time for the moroso sport compact nationals
good luck and never give up naysayers