4jx1 poor idle, no power, read on, its not the normal issues, i think

Been reading this forum for longer than i can remember, but never really needed to ask anything, until now.

Ok, we have a 99 4jx1 manual here. As above, sounds like it runs on three cylinders, and has little power.

To date i have replaced injectors (only because i managed to get a new genuine set cheap), injector o rings and copper washers, new orps and harness. Have not done sleeve seals due to no symptoms.

We have a tech2, and have run tests on the injectors, and when doing the tick test, we get perfect signal on injectors 2 and 3, number 1 is mostly fine but sometimes doesnt give five clear ticks. Number 4 will give one tick, then nothing on initial test, and nothing on following tests until system has been restarted.

So, the next step was based on the theory that there was damaged wires from injector loom plug to the ecu plug. Replaced wire for number 4 injector to ecu, no change.
Tried a spare ecu, no change.

So this brings me to this point where i need to ask the fine people on this website

I have a couple of theories left, whether they are valid, i dont know yet. They are;
1. Re check injectors by doing a tick test after swapping the loom plugs around on three and four (just in case i got a dud injector, but i feel its unlikely)

2. The earth feed to ecu is missing, or needs one. Does the ecu have an earth wire to engine or body?

Hoping someones got some ideas for me as im running out of them

Thanks in advance