Not sure if this is the appropriate section to post in but here it goes. Car is a 95 with full flyinmiata turbo and hydra. It's been intermittently losing power while running and also not starting. Car will not sputter, it just dies like the ignition was cut. It will always crank, but no spark. When this first started happening, I thought the problem was the main relay because when I turned the key on, the CEL would not come on and I wouldn't hear the relay under the dash click or fuel pump prime. I replaced the main relay from another working miata and now it starts... most of the time. When it doesn't start I have been able to troubleshoot the following:

Ecu is getting 12v at 1a and 1b harness pins with key on (=main relay is good)
No spark at any plugs
Injectors are getting 12v with key on
fuel pump is priming
coils are getting 12v with key on
resistance at coils is within specs

My best guess is ecu or CAS?

I don't know if this second problem is related or if it is something different. Most of the time the car does start since replacing main relay, and when it does it runs lean and rough. This just started happening and I haven't changed anything with the tuning. It is now idling at 15-18 AFR. One thing I noticed is the wiring from the stock O2 sensor got partially melted on the exhaust. Could that be shorting or grounding out and causing my problem(s)? Or possibly ruin the sensor? I am going to try replacing the O2 sensor and wire next but any other suggestions? Thanks!

 

02 sensor is a start. You're not going to get proper outputs if the inputs to the ECU are wonky.


CAS is your likely culprit.

 

This thread should probably be in the HYDRA subforum.
Does Hydra have something where you can take a look at the output from the various angle sensors? I believe 95 1.8l is just running off the Cam angle, so that should suffice.
Check that, if you don't see the proper pattern then there's your problem.

 

I replaced the O2 sensor with a Bosch oe replacement. Still having the same issue.

Maybe someone better at reading electrical diagrams can help me out. Here is a link to a wiring diagram. http://www.yorbalindamiata.com/images/wiring/95sys.pdf
From what I can tell, if I measure 12v at both 1a and 1b of the ECU with the key on, that means the main relay is working? Even though I am getting power at the ECU with the key on, now the CEL isn't coming on and I don't hear the fuel pump relay click.

I've cleaned the ignition switch as well. I suppose I could see if anyone local has a hydra I can swap in. Would this work, assuming I load my current map onto their hydra? I'm running out of ideas.