Hi guys, just a brief background this is a full JDM 90 T2 engine/trans/wiring/ecu(N374) swap into a first gen that, until the start of Summer, ran great for years. I believe it was July 4th weekend and I drove it Saturday and everything was running great, parked it and went to drive it the next day and thats when things went downhill.

Basically the symptons are this, hard to start, and once running idles real rough, is barely driveable, backfires stumbles like crazy. If you give it enough gas it starts making boost, but the engine doesn't seem to go over 3500 rpm or so.

I've been working on it whenever I have the time over the last few months, and have tried several different AFM's (both T2 and NA), TPS's, checked compression (over 100psi on both rotors) checked timing (dead on) have spark on all 4 plugs. Also double checked all air passages for any foreign objects blocking the airs path and nothing. I've had the UIM off several times, checking for fuel leaks, stuck injectors etc. The fuel pressure is about 38 psi, and it flows almost a gallon in a minute.

Furthermore I've tried several other N374 ECUs, as well as a N370 ECU with no change. I actually went in and made a new engine harness out of a modified NA harness, thinking something had gone wrong in the harness, but no change.

Here comes the strangest part, a N351 ECU starts right up and idles fine! I have no idea what that means, but I've checked the boost duty solenoid and it checks out, as does the pressure sensor and all the AFM's I've used....

I'm really at a loss here, any input would be helpful, I have a thread over in the first gen section here if that would help: https://www.rx7club.com/1st-generation-specific-1979-1985-18/need-help-t2-fb-guys-not-running-very-well-850270/
Sorry to be so long winded, any help is appreciated!

Thanks
Sean

 

You've got some issues.....

For lack of a computer and / or a s5 manual what does ECU pin 2b control?

 

It sounds much like limp mode, but you said you aren't getting any codes? Does the OMP check out?

 

2b is the green wire going to the AFM... Not getting any codes with any of the ECU's, and I can force codes (by unplugging something etc) so I know the code checking test light I made is working.
It does sound like limp mode but I've got several omp's and plugging them in makes no difference.
I picked up a knock sensor, boost pressure sensor and N390 (cosmo) AFM from Japan2la and tried all of them tonight. The knock and pressure sensor made no difference and the AFM actually made it worse.
It would seem logical that something is wrong with the AFM or something in its circuit, but I've tried several of them with no difference, and I still don't get why the N351 ECU would start and idle fine....

 

Yea, that is really weird man..... ive got no clue to tell you the truth. The only advice I can give is to save and buy a megasquirt or some other ECM system.

 

Sean, i'm still thinking something may be up with the fpr or perhaps one or more injectors..

 

I don't understand.

If it works with a N351.........uh, why not run it with that ECU? I must have missed something above. I'm still stoked on Ben Spies winning WSBK and Stoner winning MOTOGP today. Red letter day in my book.

And trail coils not working could not cause you problem, but Lead coil could. I know you replaced it.........but why not heat up the engine and idle it and pull the lead wires off and see if there is a difference or not. No difference would mean to me part of the problem is the lead coil assy/wiring/plugs/ECU wiring to the lead coil etc. Trail coils don't effect much of anything but that's just a opininon and one others don't agree with.

 

I should clarify, it idles smoothly and starts a bit easier with the N351, it also revs freely, but driving it with the N351 is a different matter, still has some hesitations, and if you try to get on it at all or hit boost it cuts out and falls on its face, similar to what it does with the T2 Ecu... I'll have some time this week so I'll revisit some of my earlier tests to see if I find anything just to make sure.