RESOLVED: 1/21/2016
What a bizarre failure. Turns out it was the CAS the whole time - the CPS signal failed due to hall-effect sensor internal or wiring issue causing it to pull to high (+5v). I installed a new mitsubishi unit, and also have an Allegro A1103LUA-T on the way to repair the old CAS. Either way, engine fired up on first attempt...now I can enjoy my 6spd swap.



I'm stumped with a problem that's been frustrating me for 2 days now.

Back Story:

Blew another 5spd up, so Miata has been sitting for 3 months while I put together this sweet swap:



6spd is in, no crushed wires, and work was completed without removing any major parts outside of the normal mechanics necessary for trans swap. Replaced CAS seal with viton unit due to leak, but was careful during handling.

Car was running perfectly until 5spd blew up, however, go to start car yesterday and it fired up for 2 seconds then fell flat on it's face. Subsequent restarts resulted in one loud and scary backfire. Noticed that Circuit Opening Relay under steering column is clicking in between 360 degree engine rotations, but holding relay closed I can still feel it pulsing which means that ground (white/red) is driving this intermittently.

Trouble-shooting:

• Regrounded Throttle body ground, LC1 ground to intake, main ground under brake booster, and PPF ground
• Replaced 6spd starter with old 5spd in case of excessive current draw
• Tested COPs and Injectors with MS test mode - all good
• Tested spark during starting, only cyl 1 gets spark...and it's weak.
• Reflashed DIYPNP firmware 3.3.3 and reloaded tune/sensors
• Shorted fuel pump and main relay to keep on
• Charged battery and hooked up 200amp jump, then tried known good battery in parallel (this caused voltage droop to be less severe, but still drops to 10.5v during start)
• Battery voltage during start is 11v
• Pulled MS apart to inspect for bad ground, burnt components, etc.

• Supplied a sample datalog when battery was still charging - droop is less severe now.
• Supplied composite log export

I'm taking a break from this for the rest of the night - just wanted to see if anyone has encountered BS behavior such as this. I've been googling all day and I'm running out of ideas.

Appreciate any help...thank you.

 

Did some research into the symptoms being exhibited - Fuel pump, injectors, ignition coils cycling on/off during starting event.

Used Coil and Injector test mode with plugs pulled - both worked perfectly. White/red 12v feed from ECU 1B rock solid, and grounds are good as well.

On to the CAS - as noticed before, timing was dropping off and intermittent. So, decided to manually spin the CAS wheel using my drill and observe behavior.




Same result. RPM drops off, timing seems awry, and Lost Sync Reason 38 which appears to relate to the 4G63 setting in MS.

Checked wiring at CAS harness:




Blk/Lt Grn: GND
Wht/Red: 12V
Wht: 12V (Opto in -)
Yel-Blu: 5V (VR2 in +)

All the threads I could find stated that both hall sensors are fed 5v, that's incorrect. Correct voltages for 95 Miata is as indicated above.

Back-probed CAS with it plugged into harness, and spun by hand - observed 12V sensor fluctuating, but 5v sensor was steady. Pulled apart and cleaned CAS thoroughly, which made no difference. No visible wires to repair in CAS either, because hall sensor board is molded in plastic and non-serviceable.

At this point I'm 90% sure this is CAS related. Which is odd, because there were no indications of any issues prior to doing the transmission swap - and yes, the sensor was removed during the trans so as to not have the housing impact the firewall.

Will update tomorrow - getting a $50 used unit off Craigslist, hopefully.