Did a significant amount of searching this week for a solution and found two other people with a similar issue. Neither had posted a solution. (https://www.rx7club.com/showthread.p...&highlight=CEL) I just picked up a '94 FD touring, 5sp, no mods, ~110k miles. Seems to be in limp home mode (under partial throttle, car will rev to 5+krpm; under half throttle, falls on its face [feels like complete lean condition] as soon as turbos start to spool) Here's the symptoms:

CEL on solid while driving. When checked by jumpering diagnostic connector TEN-->GND and moving the key to the ON position I get the following CEL flashes:

Sequence observed on in-dash CEL when TEN--->GND are jumpered:
1. Move key to ON position
2. CEL on immediately for ~2 seconds
3. CEL off for ~2 seconds
4. CEL on indefinitely

Sequence observed on CEL when TEN--->GND is NOT jumpered (normal KOEO procedure)
1. Move key to on position
2. CEL on immediately for indefinite period of time

Just to be sure the CEL was working correctly, I verified with a sweeping needle voltmeter the sequence coming from +B-->FEN and observed identical sequence to the above listed TEN-->GND.

I have absolutely no idea where to start from here. Most people would say it's a short or a bad ECU, but why would a bad ECU or short *consistently* flash the "on-off-on" sequence above? Nowhere in the Mazda workshop manual is this "short long (indefinite)" code mentioned.

I've tried disconnecting the battery / stepping on brake to clear codes and the above sequence remains the same. Please don't tell me to "screw it" and get an apexi power FC. I'm looking to stick with stock hardware. Thanks for any help/suggestions.

 

Screw it...go with a stand alone ecu. J/K

I tried searching your problem out and asking a few friends but we are puzzled as well. bump to the top for a difficult problem. I know how frustrating this can be...some gurus please help him out!!

 

Cool, props evot for asking a couple buddies. I know it's a tough question and hopefully we can get it solved for the poor souls who read this in the future...

 

When I've seen this before, it's been because of an issue with the wiring harness (either something left unplugged or a short).

 

Mahjik- thanks for the input. Could you elaborate a little...? Did you see the same CEL flash pattern? Also could you clue me in on what the exact fix was in your experiences? Thanks guys for your input.

EDIT: Also, as a general question, can you perhaps give me a couple suggestions on where the FD harness commonly fails? I've owned what feels like hundreds of cars and I've never had a harness issue. Thanks again.

 

My exact fix was a new wiring harness. I didn't have the patience to start checking wires. I would start by checking the connections under the dash and at the ECU. Look for anything not plugged in. If you haven't located the ECU yet, it's on the passenger side of the cockpit. There will generally be only a single black plug which is hanging, it's a diagnostic plug for the cooling system.

The FD harness just gets brittle over time from the severe under hood temps. It's not uncommon to have these replaced. If you do some searches here on the forum, you'll find threads of people buying new harnesses and then re-wrapping them with better heat resisting tape to help them last longer.

 

if you aren't pulling any codes from the ECU but the CEL is always on usually means that your ECU is fried! thats what happened with me after changing out my oil metering pump. everything was fixed that needed to be fixed but my CEL was always on but i couldnt get any codes from it.

i swapped ECUs with a buddy of mine and everything was fixed!

the ECU may be your problem! not positive about it but that just might be your problem!!!

 

Big big thanks to 94TouringFD (Matt) for helping me out on this one- he had a spare ECU from a 94 ...not touring... FD that I tried out and it cleared up all my issues. Now I'm throwing an EGR code (and a 4-long-pulse code... gotta figure that out) but the limp-home/fall on your face @ boost symptom is gone and now I've got an actually functional FD!! I'm surprised at how slow this car is! Haha that's what my FB is for though... I hope this post helps somebody out in the future. Peace out party people.

 

Glad my spare parts were able to be put to good use. I'm just happy to have a functional FD local now. Well once I'm broken in and tuned you'll have to get out the FB so we can go out and embarrass some cars in the area, lol.

 

finally put the FD on the road... wash/wax and took it to a show. Ran great. For about 15 miles. It drove about 2 miles with no CELs and then the CEL popped on - EGR, no news there. Said to myself I'd take a look at the EGR after enjoying the car for at least a couple hundred miles. While I was dropping off my friend's exceedingly attractive girlfriend (hey now, it's an FD, I had to) at her civic after taking her out for the evening, on my way home I noticed identical symptoms of "limp home" as I did before... only this is with Matt's spare ECU. Needless to say, I sighed to myself but couldn't honestly say that stuff like this happened to me rarely. I drove it back home without any other problems and garaged it.

Fast forward, I check the CEL today and instead of getting an EGR code like I had before when it first popped on with this ECU, I was back to the dreaded "no code" (see first post). I had myself a quiet little cry in the garage and decided to paint my FB instead. So that's where she sits.

My guess is a short in the harness somewhere is either grounding and/or shorting some wire such that some component in the ECU is possibly getting fried. This would suck for obvious reasons, namely the fact that I may have just destroyed a perfectly good ECU a la Matt. Not good. Looks like old bessie is gonna be settin' there for a long winter's nap while I go outside and shoot paint on a long overdue SA22C winter rat project. More updates as they arise.

 

I know on 2nd gen rx-7's a failure in the OMP (internal electrical short) can fry an ECU.

 

argh,

Thanks for the suggestion. I haven't officially fixed it yet, but have made significant progress. One of the 4 poles of the stepper motor read low - instead of the spec of about 22.3Ohm, it was at 2.3Ohm - an order of magnitude below spec.

This fried pin 4J, which correlates to pins 8 and 9 on the NEC AI400H 12-pin IC which is in charge of stepper motor control. I was unable to find a datasheet for this IC so I can't confirm it, but the case of the IC is visibly cracked and burned on the side of the IC closer to the 'A' terminals of the ECU.

I was experiencing the aforementioned CEL problem after about 15miled with the 'new' ECU with which I replaced it. I inspected the resistance of pin 4J WRT the IC ground of about 1.88MOhm. IC ground is pins 6 and 7. Even though resistance of pin 4J checked out alright, the ECU still bitched without codes.

I replaced the OMP with a S5 OMP with modified output oiling ports (from 4 to 2) and re-wired and verified proper resistances across the poles and feedback potentiometer. Coupled with the new ECU this should fix my problem. Will connect tomorrow after sleeping on the issue and post results...

 

Verified solution of problem- put about 150 miles on the car over the past couple weeks with no issues. Turns out that a low resistance OMP pole WILL short your 12-pin stepper IC - WITHOUT A CODE - rendering your ECU into a non-CEL code throwing, limp-home mode vegetable. Replacing the OMP along with replacement of the 12-pin IC (or entire ECU since it appears there is no current replacement for that IC) will solve the problem.

If this helps you, please post up something because this took about a year and a half of my life to figure out... I'll PM you my address so you can send a 6-pack

 

Sorry, just saw other thread.