I installed a full header to muffler exhaust on my 96 obd2a civic. I ran it with both o2 sensors installed, then switched to the rear o2 mounted by the header in open air. I also have cut to fit brass tipped plug wires. The car started having issues with random misfires while the engine was under load basically.
There were 2 occasions when it was the plug wire brass piece corroded in half. Replaced the brass piece and it ran fine til it happened a 2nd time, now it seems to be clean and not corroding.
Anyway the random misfire issue has returned! The way it behaves reminds me of a loose main ground wire, or TPS.
Not sure what it is, but my exhaust is leaky due to fitment not perfect yet.
The cap n rotor looks good.
Whats weird is that it seems like the same issue it had with a corroded-in-half plug wire connector but that definitely isnt the problem now.
This is my daily driver and i have people depending on me, please help me narrow this down.

 

Replace the damaged plug wire
what do you mean by:
" then switched to the rear o2 mounted by the header in open air."????

 

If you order Aurora Ignition Wires for your car you won't need wires ever again. They are probably THE best wires your can get for your car and they surpass your brass noise collectors.

 

I switched the rear o2 from being inside the exhaust to right outside of it basically. Because there is no catalyst, its an easy bypass to a check engine light. The 2nd o2 sensor basically checks that the temp is correct and that the exhaust is cleaner than before the cat. Mounting it outside the exhaust is a good temporary fix. Ran perfect like this for a month to 2 months.
From what Ive experienced, the issue is coming from elsewhere.
Maybe its the distributor? coil? and i say this because when the engine is under load is when the more powerful spark goes through.
If there is an electrical issue somewhere, then this is a sign of it being the issue.

Plug wire is completely repaired since its a custom cut kind of wire
Although i could have assembled the wire in too much of a rush and made the contact with the brass not as good as it needs to be.
The main issue i have is that its a completely "random misfire" and even throws that code for every cylinder sometimes, rarely actually. Usually when i drive the car without letting it warm up.
The only pattern to the misfiring is it will completely misfire on multiple cylinders if i give it over half throttle at low RPMs.
Or if I try to climb a hill at low RPMs. It will sound like a Subaru and sometimes worse. No offense to Subaru's lol.
A mechanic i know told me it could also be the leak in the exhaust where the header goes from 4 to 2. thats where my leak is for now. He said air can come in the pipe between pulses and throw off the readings, if its close to the o2 sensor. And thats the theories i have found so far. Electrical system, Exhaust leak,