intermittent missing fault in lowrange

[Deadduck]

Thanks for that not a barn find drive on the road sometimes done quite a few long distance trips and is completely fine 100% on the road it's only Lowrange for some reason under sort of half load engine has ben fully rebuilt top and bottom o2 sensor was bad from extractors hitting body and chopping wire off so got a new bung welded in all the spark plugs were done when rebuilt but it also done this before rebuild I have a feeling it could be my cam position sensor(hard to find over here) or ignition side of it as when it does it it blows black smoke so tells me it's not burning the fuel it has no cat and 1 muffler I will get into it and check what you have said and do some more tests. Thanks