Ever so slightly back on topic.
The FL2 engine starts up ok, after a few seconds of cranking. However it's definitely running on 3 cylinders, until its warmed up.
So I reckon it's an injector not playing ball, which is odd, because they look like they've been reconditioned.
I can't identify which one it is electronically, as it appears the PTM used on this engine doesn't record PID information or codes.
So I'm left with simple substitution as a means of identification. I suppose I could unplug each injector in turn, until I find the one with the fault, but this carries an element of risk to the injector driver circuit.
So that leaves substitution as a primary way to identify the duff one.
My thought is to change the injector, that was in the cylinder with the issue first. This injector could have been damaged by numerous hits by the nut, as it bounced about in the combustion chamber. The injector pintle is pretty sturdy, but I'm thinking that maybe the impacts have jarred something inside, causing it to stick.
Any other thoughts or ideas on this are most welcome.