why is the 2nd and 3rd valve not firing the spark plug looks like brand new.. on 2003 Mazda B2300

i got sold wrong plugs but didnt look at the plugs when i put them in and ran it like that for a month then notice that i had the wrong plugs then changed it and still the same.. The first and 4th spark plug has black carbon on it so must be working .. please let me no what going on if i melted the pis tent rings.... oh and my muffler from the manaflod down to the end of pipe was bright red..

Asked by for the 2003 Mazda B2300
ck compression on those cyl to start with. then go from there
okay ill get back too u i was thinking if the sencor in between 2nd and 3rd had anything to do with it let me konw...
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