Missfire? question Jazz 2005 CVT

[CPJ]

Hi all, I have a 2005 Jazz with only 60k on, changed all 8 plugs as miss firing under load , confirmed by OBD that friend has. (note: had to gently drive it 200miles as on a long journey when misfire started) Once changed the error code cleared. Starts on the button and revs clean however still 'misfiring' (but not as bad) under hard acceleration. Done the 'old school' thing and popped some redex in but only just, so no change yet. No eng check light etc, would another OBD test pick anything up? Any advice on where to go next appreciated. Thanks in advance

[Lord Voltermore]

Could it be coil packs, power supply to coil packs  or a plug lead from coil to plug?  Might be worth checking connections for any sign of being loose, or dirty/corroded terminals .  The obd reading might be able to show which particular plug is misfiring  which might speed up diagnosis  . But I dont know to what extent it can identify which particular component is causing it.

   But my knowledge of cars with an ECU  is limited.  Please dont replace expensive parts on my suggestion alone.