Low voltage, sputtering issue.
 

Someone please help!
this issue has been a problem for over a year and I cannot figure it out. I have a turbo 1.6, mspnp2 running e85, car was dyno tuned and ran perfect for a couple months. Now the car sputters with higher loads/high rpm. Replaced all 4 Ls coils, changed plugs, cleaned injectors, added fuel pressure regulator with gauge, changed tps, checked grounds, no fix. Rarely the car won’t sputter at all and pulls all the way to redline just fine. But that majority of the time it sputters over 50% throttle. Every time I crank my car to start my AEM afr gauge says “batt” which means low voltage, I have replaced the battery, stater, and alternator. Still slow crank, sputter, and low voltage. I tried to put my stock coils in and the sputter changes into backfires and gets worse.
my Instagram is Official_mx5 if anyone wants to hit me up and help out.

Have you checked your grounding to the chassis
 

Have you checked all of the grounding to the chassis? There are several areas that you could clean and make sure you have good metal to metal grounding.