I recently took my perfectly running NA 13b out of my 87 RX-7 and put it in another body of the same year, and since then haven't been able to get spark or a pulse from the fuel injectors. I did the transplant without touching the engine harness (I just unplugged it at the ECU and brought everything over like that).
Even though I think it's safe to assume the engine harness isn't the problem, I went through it again and secured all the connections and grounds (including the one under the throttle body). Re-did ALL the body grounds too as best I could. Even though I saw some improvement, the car still did not want to start.

When I turn the key to "on" position, all the warning lights come on. I am told this is normal, and is an indicator that the ECU is powering up (correct me if I'm wrong). The fuel pump turns on, and the gas gauge shows the right amount in the tank. The main relay clicks too, and successfully passes on 12.5v through the b/w wire and the blu/w wire. All engine bay fuses are good and the connections are clean and tight. Interior fuses are all good as well, I even swapped the 15a engine fuse just to be safe.

So basically this is where I'm at:
Everything is getting juice where needed, but it seems I'm missing the signal for the injectors and coils to fire. Injector connectors all read 12.5v, and the coils are both supplied with 12.5v. Turning the engine by hand, I am NOT getting the 0-5v signal at the g/y wire at the leading coil. I am getting 12.5v at the b/w on the three wire check connector, which I'm told is a good thing. Also, I'm getting 5v at the br/w wires at the pressure sensor and at the TPS, which I'm told indicates the ECU is getting power. I ohmed out the terminals on the CAS, and everything is within spec. Now, according to this thread, which has been the most helpful to me so far, I should be able to get between 100-200 ohms between the blue and green/red and white wires on the ECU side of the CAS(true or what??). I'm getting no reading at all. Also, I think I'm right in saying I should get the same reading if I ohm out the leads at the ECU plug (this would give me the resistance on the CAS itself). No reading still.
Remember, I am using ALL of the same electronics from the old car where the engine was running without a problem. Same ECU, coils, sensors, fuse box, CAS. I have tried two different ECU's and get the same results. The only thing I haven't tried is another CAS, but I don't think I should even have to touch it.

Please help, dudes. I've been on forums for days reading about everyone's startup issues, and I can't seem to find a solution. My car is all put together, I just have to track down this pesky electrical problem so I can drive away happy.

 

So, when you ohm out the CAS wires at the CAS plug you get 110-210 ohms as stated in the FSM, but when you perform the procedure at the ECU you get no readings to speak of? Is your ohm test at the ECU done w/the ECU plug housing the CAS wires unplugged from the ECU? The Green and Blue CAS wires are to be ohmed as are the Red and White wires.

 

Yeah, the first time was with the big plug UNplugged. But I checked resistance on the blue and green/red and white wires at the CAS connector(not on the CAS itself) and got no reading as well. Am I checking in the right place? Should I have key to on or off?

 

You don't need the key to perform an ohm test.

The CAS plug connects to the engine harness which connects to the front harness which then plugs into the ECU. If you are testing at the connector which mates the CAS to the engine harness on the engine harness side of the connector then perhaps the connection between the harness and CAS is a poor one. You should be able to test at the CAS pigtail itself also. And it is best to to place the meter leads into the back of the plug so as to make strong contact w/the wire pins or the meter won't read properly.

 

I already tested the CAS, I get about 160 ohms between each pair of terminals. I think there is a break somewhere between the big ECU plug and the accessories it runs. Is there a connector somewhere that mates these to the rest of the car? Or a crucial ground I missed? I already checked the three connectors by the driverside strut tower, the connections are clean and tight. Maybe there's something under the dash I'm missing? Some security measure I don't know about that would prevent the car from starting under certain circumstances?

Last night I did try one thing. I have a donor RX7 from which I cut the CAS pigtail and used it to wire it directly to the ECU. Now, with the CAS wired directly, I get the proper ohm reading at the ECU plug. But not with the original harness. Still no spark or fuel injector click. Any ideas?

 

Not sure what you mean by the three connectors near the strut tower. FE-04 mates the engine harness to the front harness and it is this connector which houses the CAS wires and it's located near the trailing coil. If you located this connector you could unplug it and take the ohm reading on the engine side of the harness. If the results are good then you ruled out one segment of the wiring harness and your focus should be on the front harness (this is the one that is found at the ECU as it relates to the CAS wires).

 

Yeah, I meant those three white connectors that mate one harness to the other. I guess FE-04 is the four-pin plug then. I ohmed it out, and the engine side of the CAS harness checks out. So I guess the break is somewhere underneath the dash, because that's where the rest of the wires run through. I took a good look under there, there isn't any obvious damage to the wiring at all, but there are a few unplugged connectors, the fuse box and the other plastic box next to it are in there pretty loosely. Not sure if these have anything to do with it, but I'm going to compare with the old car and see if I can find something.
I really appreciate the input btw. A week ago I didn't know where to start, and now I really feel like I'm closing in on this bastard.

 

The wires of the front side of the harness travels directly to the ECU. Set your meter to continuity and test the front harness. To do this the harness needs to be unplugged at both ends (FE-04 and at the ECU). W/the meter set to continuity you place one meter lead to one of the four CAS wires in at the front harness at FE-04 and the other meter lead to a known ground and if the meter rings out then it means the wire is grounded out which it should not. Do this w/all 4 wires related to the CAS and you should find which wire is the problem cause.

If by chance the meter does not ring out then do a conventional continuity test where the meter is placed to one specific CAS wire at both ends of the front harness (one at FE-04 and the other at the ECU plug) and you'll see if there is a separation in the wire.

 

If the wires run directly from FE-04 to the ECU, then why do they change colors at FE-04? They leave the CAS with the original blue/green/white/red wires, change to y/l, l/r, br/y, and l/y, and somehow end up l/g/w/r again at the ECU plug. There must be another connection I'm missing somewhere.

Anyway, I did the continuity test to see if any wires were grounding out and got nothing. Going to test from ECU plug to FE-04 as soon as I get a lead long enough to reach. But I don't think it matters much, because I've already confirmed the problem is in the body harness somewhere. On top of that, I tried wiring the CAS directly to the ECU and it still doesn't start. Since I did that, I now get the 5v signal at the g/y wire at the leading coil, but that's the only thing I can tell that's changed. Still have voltage all around the b/w wire that runs to the leading coil check connector, still have power to coils, and I even verified at the ECU that all injectors are getting ~12v. What else could possibly be missing, even now with the CAS sending the proper signals to the ECU? This gives me reason to believe that the problem isn't only in the CAS wiring, but possibly even all the wiring running from the big ECU plug.

 

I'm relying on the 88 wiring diagram so perhaps the 86-87's are different or perhaps you have the CAS wires plugged into the wrong connector near the trailing coil (a continuity test would tell you way or another). If the car does not start it could be the timing is not set properly. Have you verified for spark and fuel?

 

Must be the wrong connector because the cas wires are shielded and do not run through a junction, so they should be l/g/w/r from the cas all the way to the ecu...no color changing.

 

Y/L, L/R, Br/Y and L/Y is the plug for the trailing coil so you have the engine harness from the CAS plugged into the trailing coil. Incorrect.

 

I just came here to post the same thing.

I think we have solved the problem.

 

Funny, I came to post that I had just discovered the plugs were in the wrong place. Silly me.. Well, it's a relief, and it explains a whole lot.

So the wiring is good for the CAS and the coils. One step closer to getting it running except my leading coil doesn't spark, and I'm still not getting fuel. I'll have to check the wiring again, but last time I checked the leading coil was getting power and the 5v signal, and the primaries were getting 12v at the ECU plug. Check back in later..
Thanks a bunch, dudes. I have no one else I can ask about this kind of stuff, so, again, I really appreciate the input.

 

The coils need to be firmly bolted to the fender to be grounded or else they won't work. Perhaps this is your problem or the ground needs to be cleaned up and improved.

As far as fuel is concerned you need to check the circuit opening relay under the dash and to the right of the steering column. The top left wire needs to have voltage w/key to start. If it has this voltage then the Blue wire in the plug, which powers the fuel circuit, needs to have voltage.

Also, was the engine replacement a USDM or JDM as the fuel hoses are switched.

And the voltage on the primary injector wires at the ECU should drop to 6 volts or so w/key to start. This tells you the ECU is trying to activate these injectors.