Hello all. I recently picked up an s13 with an S1 RB25det in it on CL for cheap. Bought it knowing it was an incomplete (missing IC piping and exhaust) swap and didn't run, with the intention of finalizing the missing pieces. It came with a Wiring Specialties harness.

As of today, I have finished the IC piping and exhaust and cannot get it to start consistently.

Symptoms:
-Will only start with the Coolant Temp Sensor unplugged. If the CTS is plugged in, it will not start at all. It will kick slightly but will never fire. If you start the car with the CTS unplugged, and then plug it back in while running, it will die almost immediately. When running, it feels like its misfiring and is very rich.

Here is a list of the things I have tried...

-Verified wiring from ECU to CTS is correct

-Visually inspected harness for crossed/frayed wires. Looks ok.

-Checked and added a few more grounds to the head and block. Ignition harness ground wire on the coil pack bracket is intact and tight.

-New battery, and hooked to a battery charger while testing.

-New plugs (BRK-7e) gapped to .028

-Inspected ECU motherboard. Doesn't appear to have any corrosion or broken links. Tried a different ECU that was in supposedly in good running condition. Will not run with the CTS plugged in or unplugged. Visual inspection of the motherboard looks to be fine.

-Tested CAS by removing and spinning by hand. Can hear injectors click but only get consistent spark on cylinder 1 & 6 when grounding out the plugs. I tried moving the coil packs around, issues does not follow the coilpack. Cylinders 2-5 have inconsistent spark. Replaced CAS with a refurbished one and have net the same results, though spark appears to be stronger on cylinder 1 and 6. 120 and 1 degree signal wires are correct according to an R33 ECU pinout.

-Tested Ignitor for resistance and found there to be no resistance on several pins. Replaced Ignitor, no change.

-Pulled fuel rail and had injectors flow tested and cleaned. Lower o-rings were torn on most of them. Repaired and replaced, no change.

-Tested all connections to MAF, ignitor, CAS, CTS, Ignition harness for continuity and power. Everything looks right.

What am i missing?

Actually TESTING and /or replacing Coolant Temp Sensor ITSELF ,with a "known good one" ??
Unless I missed something - going just by what you wrote ?

Replaced with a new one from the dealer.