Okay so my over fuelling issue is still there. I thought it was all fine but went to start the car today and it seized (overfuelling). So I straight away pulled the spark plugs out as someone had told me that it seizes if the cylinder fills with fuel as it can't compress the liquid. Spark plug on cylinder 1 was soaked, all other were dry. So I know cylinder 1 is overfuelling.
 
Here is my big question. I pulled the injector plug off cylinder 1 and cylinder 4 to test (as these are the only ones I can access easy) with a multimeter. Both did the exact same thing. When I turn the key to start, not cranking the engine over, they get about 10volts or so (initial fuel pulse) but then the voltage will slowly drop till it reaches 0. It take about 20 seconds or more to drop for say 7-8volts down till it reaches 0. Is this normal?
I'm trying to determine if there is a fault with the injector being stuck open or if the ECU is stuffed. I know that the fact cylinder 1 has a soaked plug and the others didn't point to injector 1 issue but the 20seconds for the injector to drop to 0 volts seems odd to me, however I am no expert on injector pulses. Any definitely know the answer?

Checked all the grounds etc?  On back of intake manifold and engine to chassis?

Yeah grounds are connected and all seem fine. I just need to know if this voltage reading is normal as there is nothing I can find on the internet about it. The injector signal voltage drop from 8v down to 0v is like a capacitor discharging but I don't know if that normal especially for that length.

I made extra earthing cables.

Throttle body top bolt to chassis
Plug loom bolt to chassis
Double earth on head bolt opposite oil cap to under strut top

Up to you where you put them but I did those and they helped

Are they new plugs?

Actually all good. Most likely its injector 1 stuck open. They siad if the ECU does the same thing on plug 4 and plug 1 then it would be working right.
I'll do a test tonight where i'll unplug injector 1 so its getting no fuel pulse, then crank the engine and see if the plug comes out wet. That will tell me if its stuck open.

are you talking 3SG*?
 
normally with toyota wiring for injectors its always 12v. it doesn't get lower (maybe 11v or so for normal running drop). 2 wire injectors have 1 constant 12v power which is the main sensor power coming from the EFI main fuse/B+. and then the ECU grounds the other wire in batches. grounds 1&4 together and 2&3 together.
 
so if your getting 7-8v or whatnot that is odd. unless 3S motors are completely different to all other toyota motors/electrics
 
 
If your running the motor and have a mutlimeter on it though it might explain it, the pulses are way too fast for a multimeter to catch. so if your holding the pointers bewteen the 2 wires on the injector plug this won't be giving you any good readings you can do anything with.

Yeah I was doing to the test wrong. I had placed the positive and negative into either side f the connecctor. Instead I have to check one side at a time. Yeah one should be12v constant and the other should receive a pulse probably too fast to read unless testing with an anoid light 
I'll do a retest tonight the right way. Been a while since I wired up an ecu, all I kept remembering were the ECU's ground negative. It's a Gen 3 MR2 by the way witha  mines chipped ecu.
I'm fairly confident the ecu will be alright. If i see a constant pulse from one end of the injector plug I know its the ECU telling the injector to stay open. If not I either have a fully stuck or partcially stuck open injector, a leaking injector, a damaged oring or a sticky injector. Either way with the last 4 the injector has to come out.
I ordered a set of new injectors already.
 

Actually Wiso reading your last post about the injection being batched 1&4 and 2&3, I'm almost certain its a injector fault. I thought the Gen 3 3SGTE might be sequential injection? If its batched then definately is the injector otherwise cylinder 1 and 4's plugs should both be soaked in petrol.

easy to tell if it is batched. pull the connectors on 1&4 and check continuity between the 2 grounding wires. not the power. if they have continuity they are batch. if not they are sequential. if sequential could still be an ecu problem. if sequential i would check for continuity between the ground on problem injector and a body ground.

I'm not sure what you mean by checking the continuity between the ground wires? Checked the positive side its receiving 12volts. I did a few test today to work out if its the injector or ECU but still can't tell. I know that the injector is not stuck permanently open.
Okay so before doing anything today I pulled the spark plug out to see if the cylinder was filled with fuel (incase the injector is leaking when closed or stuck open) there was no fuel in the cylinder. Unplug the injector and started the car with no spark plug in, no fuel came flying out. Plug the connector back on started the car without the spark plug in, no fuel came flying out so still an intermittent problem. Put the spark plug in started the car and all running fine doesn't smell of fuel. Checked the spark plugs, cylinder one plug was a bit wet, just slightly all the others were dry. Started the car again and unplug cylinder 4's injector plug while running. the idle dropped and engine was stumbling. Did the same test on cylinder 1, the engine also stumbles BUT not as noticeable as cylinder 4. It still runs a bit different but not as bad as cylinder 4 being disconnected. I pulled the plugs out again and they were all dry.
So I know its not completely stuck open however yesterday it did put enough fuel in on cranking (after not being started for 3 days) to hydraulically lock the cylinder. So I'm not sure what the issue is. Either the ECU is intermittently telling the injector to open fully sometimes or the injector gets stuck open sometimes....Can a fully open injector put in enough fuel to hydraulically lock the cylinder on cranking or would it have to leak fuel in over night?