Gen 3 3SGTE swap

Hey guys, recently I swapped a jap GEN 3 3SGTE into my 1997 Bathurst mr2.
The turbo motor was running in a donor car prior to the swap and I have removed all the running gear and swapped into my NA shell.

It runs the standard gen 3 wiring loom harness with a apexi power FC ECU.

The problem is it is only running on 3 cylinders and it blows a fuse whenever I try to fire it up by the ignition key!

I have put in a new injector resistor pack, new plugs, my walbro fuel pump is running off a different circuit, all 4 cyls have great comp as it is freshly rebuilt with forged internals so none of those is the issue,
Please let me know if anyone on here has had the same or similar problems!
Could it be an internal short in the ECU! Any help appreicated, thankyou