1.0 AUC evasive misfire problem.... (Lupo)

Happy new year all - I wonder if anybody here is knowledgable on the AUC engine as fitted to my 2003 Lupo, as I am at a total loss as to what is wrong with mine. A month or so ago it started misfiring.

I replaced with a brand new ignition coil, HT leads and spark plugs to eliminate potential spark problems. The misfire remained.

With the engine running, unplugging injector 1 does not change the idle. Nor does unplugging the HT lead. So the issue is on cylinder 1.

I swapped the injector on cylinder 1 over to cylinder 4. The problem stayed on cylinder 1, so the injector is not at fault.

I ran a compression test, and all 4 cylinders sat at 125/126PSI, so it has compression.

I read somewhere that the ECU looms can fail and short out, so I began hunting for a Lupo to have a loom off.

Yesterday, I found a Lupo with an AUD engine (very similar to AUC) in a local breakers yard, and had the injector loom & fuel rail with injectors off it (same part #), as well as the loom as it runs to the ECU.

Today I fitted the replacement injector wiring loom. The misfire remained on cylinder 1.

I then fitted the replacement fuel rail & injectors. No change.

So, I removed the battery to inspect the wiring which runs underneath. I connected the battery to the terminals using a pair of jump leads. By wiggling the wiring loom, I hoped to isolate any wiring issue.

But when I fired it up, it cut out after a second, as it would if I had an immobiliser issue. Even after putting the battery back in, it still wouldn't run.

So now, instead of having a misfiring Lupo, I have a non-running Lupo. 

Having spent a small fortune on air suspension this (last) year, i'm pretty gutted I can't get it running again.

Any ideas as to what might be wrong with it would be greatly appreciated. Thanks.