My Legnum has given up the ghost!

[Wesson]

I'm very old school, with car engines so I stand very little chance of sorting out a problem with my Legnum!
But I don’t intend on giving up just yet!
My car started a sort of misfire several years ago on start up after it had rained on damp conditions, she would struggle up the road until warmed up then it would clear and no more problems. When I say misfire no popping or banging its as if no petrol to ignite?
This only happens during the winter and on odd occasions, its been in a local garage (on the I.O.W), twice, Both times they stuck it on a diagnostic but found nothing was amiss?
Well yesterday it was damp but she started as normal, traveled up the road and just got on to a bit of dual carriage way and lost power to what seemed like three or four pots? then down to one pot firing, then random, I could with a bit of coxing get the reves up but as soon as engaged the box it died down to one or two pots firing?
Managed to crawl down the carriage way and parked up, turned off and started first time but only one or two pots again?
Garage (Bexhill) picked it up and took it back, report from them that they could not make sense of the diagnostic, reading between the lines they had not or could not get hold of the correct Legnum Diagnostic data?
Outcome is car is back home and with a decidedly flatter battery and wont fire at all now.
Around two weeks ago I bought a new distributor cap and rotor just in case it was damp getting into it, worked fine after that so that's not the problem.
I have charged the battery back to full power re-attached it and engine, turns over no problem but now nothing is firing up!

I really don’t know where to start on this?
Any pointers as to where I should start would be gratefully received as I am a bit loathed to scrap her even though she is getting on a bit and has 150k on the clock, has been the best car I have ever owned!
I am thinking petrol pump? where ever that is?
or do these have an inline fuel filter, if so where might that be.
Or can I get something along the lines of a Hayes manual for this i can download?

Thank you

[Wesson]

Title should read My Legnum has given up the ghost!

[adaxo]

What engine we talking about?

[Wesson]

Its a 2.5 V6 engine model 6A13 non turbo!
I tried starting it again, still no go just the occasional fire!