I've been going over my car inch-by-inch to figure out why it's not starting up (or running longer than four seconds). I'm not really worried about it as I have a huge back log of threads just full of things to check. It's only a matter of time before I find the culprit.

However, something I haven't seen on these forums but I've seen on other car forums is that problems can rise up from tinkering with the exhaust system. Right now my s13 has no exhaust piping after the exhaust manifold. This was to make it easier to load and unload the car onto trailers. Could this be causing issues getting it to run correctly? I assumed this lack of exhaust piping would only effect vehicles with two-part 02 sensors. The ca18det only uses one exhaust gas sensor and it's located on the manifold. Logically this tells me it shouldn't be an issue. Am I wrong?

I realize an easy answer would be to hook it back up and test it out, but I only have access to my car on the weekends at the moment.

So... is your turbo still on the manifold?

If not, lack of runner length and backpressure may be messing with mixtures and airflow in and out of the head. Engines don't like to run without some amount of exhaust piping.

If your turbo is still on I would start looking elsewhere. These engines should run fine without exhaust post-turbo.

Yea, running no turbo MAY cause an issue, but if the turbo is on there, I've run on the stock ECM with no exhaust post turbo multiple times and never had an issue.

Sorry for the delayed response. I'll just go ahead and assume it's a non-issue then. In case anyone's curious, or thinks they might be able to shed some insight purely on sound alone, this is what my car sounds like when trying to start: https://youtu.be/rTHgKLOkq_s

Keep in mind it sounds extra funky due to the exhaust missing as mentioned before. I also apologize for the camera shaking. I was resting my hand on the steering wheel without thinking about the heavy vibrations.

Here's a list of things I've done so far, excluding tiny things that shouldn't effect it:
New ground connections
New spark plugs
Confirmed spark on all four
Checked spark plug gap
Checked wiring harness for diagram consistency
Bought replacement ignition switch
Bought replacement ignition coils
Bought replacement fuel pump and sending unit
Compression Test with open throttle (180, 160, 160, 170)
Cleaned MAF
Replaced gas with 91 octane
Cleaned IACV
Tried replacement ECU