Graham / Matt Bit of a long trek for me, also likely to be snowed in by then which happens every year now, so no chance of moving the trailer.
Mine is a standard 1800 K series 140 BHP EU3 but with Z & F tuning.
Graham, as yours is the same apart from the Z&F (I think) I could take my ECU off and send it to you.
(As long as you don't send me yours back 😬)
You could then test with your ECU and then replace with mine test again and see if there is any difference!
Alternatively, Mark at Z&F may have one you could borrow.
John B