Starting issues after piggyback ECU removal

[tofu20v]

I've got a blacktop 20v engine in my ae86, with the blacktop A/T AE111 ECU that has a HKS FCON VPRO Ver2 piggyback ECU. This version is only tunable by professionals with the software who read Japanese, and seeing as my engine runs too rich (even for a 20v) and is running awful in the cold weather - I decided to try out removing the piggyback ECU and just using the factory ECU for the engine.

I removed the harness adaptor that placed the piggyback into the ECU wiring mix - not much mess there. Only four wires are separately left over from the HKS piggyback: IAT, MAP signal + ground and 5V sensor output. The car has an extra HKS IAT and MAP sensor as well as the factory ones - so I'm happy for those to be ignored as I assume a previous owner in Japan just added them to go piggyback but left the factory MAP and IAT sensors wired in (the factory one was plumed into the vacuum hoses before and misfired when I got the car).

I tried starting the car up, knowing it probably wouldn't start, and the dash etc everything would go on as normal, I could hear a whirring that I assume was the starter motor spinning - but there was no attempt to crank. I've troubleshooted and dealt with a lot of starter issues this year, so I'm pretty confident the whole engagement system of the gear to flywheel is working - I imagine it's that the trigger wire is not getting power like it should? When I tried to crank the engine, the battery went flat after several turns with me persisting for a few seconds for some (also hasn't been driven too much lately) which also makes me think the starter got power to spin but just not engage.

I figured it might be my immobiliser, so I removed that from the mix which again was just a harness adapter placing the immobiliser unit in series to the ignition barrel. No leftover wires there that I can see.

I'm confused or ignorant of what wire from/to the HKS piggyback ECU could be interfering with the engine cranking, any ideas?

Thanks

[tofu20v]

Ok interesting update, I put my battery on a charger for a bit and put it back in as it somehow reckoned it had already recharged (also made sure the negative terminal was properly on rather than slipped on and not tightened) and the car was cranking. It didn't start firing - but I also know the MAP sensor isn't hosed in to the right vacuum port right now and I only did it for a few seconds as it's late. Will investigate further.

[tofu20v]

got it to run with some easy start, shame it's PISSING it down right now but I'll see if it holds idle or if there's a fuelling issue

[Corey20v]

Wondering if you have stock injectors. Likely not.
Silvertop injectors oem are like a fax machine / 90's PC yellowed plastic beige..

I've had issues w fuel pump/relay just not being happy with a low battery on my s13.. it would crank slowly, but couldn't keep the fuel pump going reliably. After charging/"restoring" with a noco genius battery tender it was fine..