Fault finding checklist?

[Cool Jesus]

Injectors can seize due to contaminants along the fuel path. Micro filters can clog up and old fuel can varnish the needle and seat and clog it in the closed position. Since your taking your time, grab a small appropriate container, chuck in the injectors with some fresh fuel and give them a good shake each time you walk past them over the course of a week.
With a multimeter you can check their resistance, which if within spec, they should be fine. I'm guessing they're a bosch injector, there's a number on the side which if you post up I can give you what the resistance should be. A quick way to see if the needle is stuck use a 9v battery and connect to the terminals momentarily. You should here a click of the needle being moved.
You should then be able to find a service kit for them to replace the micro filter and o rings. Swap them out and rig up an air hose and switch to blow some carb cleaner through each injector and presto clean injectors.
Not sure if I did a post on DIY injector cleaning. See if I can find it, if not ill pot a picture here of my simple set up. There's plenty of posts on other forums too, just adapt it to your needs and don't over pressurise the injector or hold the power on.

[Cool Jesus]

OK, I didn't do a post as I think there was enough on the web for others to get by. After a good soak in fresh fuel and change of micro filter I filled the attached hose with carb cleaner (not brake clean, carb clean is made for fuel varnish and carbon build up, and is a stronger solvent) and toggled the injector until the cleaner stopped spraying. Here's the set I used on all my Alfas and non Alfas. Worked a treat as the power source I had, had an on/off switch for the power which I toggled whilst I ran the air hose at about 50psi for this set (individual fuel pressure may be different).   

[Jekyll and Hyde]

Before ripping the thing apart, did you try new spark plugs?

[CraigGTV6]

Yes, they look pretty new, but cleaned them anyway. All 6 bench test fine.
Didn't make any difference to the starting issue.

[brook308]

Cool Jesus' is on the money with how to clean injectors DIY.
The jetrontic injectors should Fire with a AA 1.5v battery as they are low impedance.
The v6 I had to clean had sat for several years so my fault process was,

1) Check fuel pump by turning the ignition on and holding open the air flow flap, the fuel pump did not run. Checked the infamous double relay in the engine bay it was stuffed. Replaced the double relay with a spare, now I had 12v at the fuel pump with the air flap held open but the pump was also seized. I replaced the fuel pump and now had fuel pressure at the injector rail.
2) Now I had fuel pressure but the engine would not fire. I sprayed aero start, well butane gas actually, into the plenum and the engine would fire on the butane so I proved I had spark.
So either the injectors were all stuffed or the ECU was not firing the injectors. I thought it highly unlikely that all 6 injectors were blocked, surely at least one would work, but no nothing.
So I wasted a lot of time tracing ECU circuits and swapping out the ECU to no avail. I did however learn a lot about jetrontic on the way.
3) The jetrontic ECu fires all 6 injectors at the same time and it does this by switching the ground connection to each injector not the +12v. So it is difficult using a multimeter to test to see if the ECU is firing the injectors. This is where a logic probe comes in handy. You can buy them from Jcar for stuff all. Connect the probe earth lead to the vehicle ground an the whilst cranking the engine put the probe on earth leg of the injector loom connector, any one of the six will do they all fire at once. The leds on the injector probe should flicker indicating the ECU is switching earth or ground and hence is trying to fire the injector, the other pin of the injector connector should have a permanent 12v dc.
My ECU was trying to fire the injectors but  all of my spark plugs were dry and all of my injectors were seized.
4) I pulled out all of the injectorts and tried to fire them with a AA battery but they were stuck solid so I simply cleaned them and also had to put some pressure on the solenoid pin of the injector to release it. After reassembly this engine ran fine until it was replace with a 3 litre for some more power.

[martym00se72]

Whilst doing all this work it might be a good idea to replace water pump and timing belt so you are starting with known good components there. I also imagine you have checked timing to see everything is lined up as that can have an impact on willingness to fire...

[CraigGTV6]

Ok,
Did a bit more today, following cooljesus advice and setting up an injector cleaning apparatus.
Will post up a pic of it tomorrow.
Found that one O ring where the injector seats was badly damaged, probably through careless installation on some previous occasion , so that was good.  Looking at the o rings , I thought they looked similar to the family Falcon ones, also Bosch injectors, so I cruised on down to the local Ford dealer to grab some new ones....
$3.00 EACH !!!!!!!!    Grudgingly, I handed over my cash with shaking hands.
Feeling I had been stung I stopped at Repco (my least favorite shop) on the way home to see what they had, and could have bought a bag of 100 , the only qty they sell, for $67.
No wonder people buy stuff online. I'm a small business owner myself and try to support my local businesses wherever possible, but sheesh, sometimes I wonder what it's costing me...
Anyway, today's questions are:
Should the injector stream be a thin stream like a hose, or a misty fan/cone shaped deal?
Mine are all thin. All seem to see flowing the same amount.
And 2: the impedance I measured was between 3.6 and 7.1 ohms.  Spec for these injectors is 2.4 ohms.  Is this a problem?  Injectors are part no. 0280 150 105

What I am really pleased about at this stage is that by taking this thorough approach,  I'm finding a number of small issues which I hope are adding up to the starting/never running right issues with this car.
Chow for now,
Craig.

[CraigGTV6]

Here's my setup, using the injector rail off the car.
Block fuel inlet, block fuel outlet at regulator, add fuel filter & extra line with air fitting at cold start injector hose, fill line with injector cleaner, pressurize to 40psi, then toggle the injectors individually with a small 12v battery.  Hey presto, no more prostate problems for my injectors....
I used about 250ml of cleaner and a fair bit ended up on the bench due to various issues, but worked well and would do it this way again.
Thanks to cooljesus for the idea.
Craig.

[CraigGTV6]

Another pic

[Cool Jesus]

That's it, feels great playing around and building test machinery.
It's not all bad news for the injectors from the manuals I have. To start with you have the correct injectors - tick.
I haven't looked hard but from a chart I have it's a low impedance injector which should range between 1-5 ohms. I stand to be corrected, however the higher the impedance the more resistant it will be to open. It would need a higher current? They opened well with your 12v, but I don't believe the signal voltage would be that high. I don't believe this is an issue for immediate attention, just keep an eye open for spares as they pop up and replace the higher value injectors later. They're doing ok considering theyre age.

Anyhow, the run at 43.5 psi and flow at 190.2 cc/min. I'm guessing they have just a single oeiface so the spray pattern will be more of a stream than a most spray. You can check by holding tissue or cardboard a determined test distance etc, bit they seem to ok. Not clogged!
I would have ebayed a service kit with o rings and filter basket for each.

Did you get a hold of the jetronic service manuals? I keep reading about how invaluable they are for repairs and trouble shooting.

Edit - I could be wrong about the current to the injectors? Just read brooks post and I'll stand back on my hypothesis, as he's had hands on with this system

[GeeTV]

Don't think I've ever seen a rear wiper blade on a gtv6 before!?!?!

[CraigGTV6]

IT LIVES!!!!!!!!  HA,HA, YEAH BABY...

Hooray, after much delay, it fired up today and sounds sweeeeet. ( apart from a little valve noise )
Main problems ended up being the fuel pump, and the little donut o ring that controls the idle speed.
I followed the checklist to the letter and it was extremely helpful, couldn't have done it without. I now have a very good understanding of l-jetronic, and how it works in this vehicle.

My big issue now is an oil leak , reasonably severe , which seems to be coming from the timing belt de tensioner  area.
Is this a known problem?? Does it have a seal or something which may have failed??
It also appears to be difficult to get at.  Does anyone have a V6 engine Manual or section thereof which deals with removal and installation of this? My old Haynes manual only covers the 4cyl brigade. Doesn't seem to be any v6 manuals on eBay either...

Will now change all fluids , give it a clean up and have some fun! 
If I can fix the oil leak.
Craig.