I recently pulled my plugs and marked which cylinders they came out of.

Under a magnifying glass, the further back in the engine (5,6,7 & 8) all show higher levels of deposits on the plugs, with 7 & 8 showing the most.

Should I be adjusting the fuel balance to bring them more in line and how would I know how much to balance with? Would it be wise to just trim a couple of percentages off the existing number? Which way adds fuel and which way subtracts fuel.

Since I have a S/C, I am very hesitant to run too lean and just putting a A/F sniffer in the tail won't identify individual cylinder issues. If I was to show a 12.5:1 at the tailpipe, that could translate into an AFR of 14:1 in cylinders 1-4 and 11:1 in cylinders 5-8, or something in between. None of which is optimum.

I've heard of an EGR scanner and if so, then what to look for?

Thanks,

UD