99 GMC 2500 7.4 PICKUP- part 2

[RACECAR]

Another question i have besides the engine number is i am trying to get it to pass emissions which it failed with high hcs bad , so tuned it up plugs cap rotor wires air filter all GM going to change oil tryed to retard the timing , found that won't work on these 454s had a scanner on it i was i believe in range this engine runs perfect except for a small skip while it is idleing no hesitation when you press the pedal at any speed does not smell rich while at idle it is a 5 spd will look for all the vacuum lines i think this is a replacement motor the truck has 177000 this thing runs to good for a 177000 mile engine any hints on the high hcs and the slight skip at idle? Thanks.

[GM-Tech]

Does it have the original o2 sensors? That'd be the first place I'd go if you want to guess.

[RACECAR]

Does it have the original o2 sensors?  That'd be the first place I'd go if you want to guess.

 

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Thanks for checking the number, if this has 2 o2 sensors i better get my book out and figure out what they do thanks.