ive been trying to trace a missfire on my 4.6,ive replaced maf,ignition leads,spark plugs,coils etc(cam is new)without any success,snap on reader states that it is misfiring on no1 and no8 cylinders.it also appears to get better the warmer it is.how reliable are the petrol injectors on these things?i notice that island 4x4 do replacements but ive never regarded petrol injectors as a service item before,is it plausible that the injectors have an issue?