My Uncle has a 99 lightning with the following mods, diablo chip, JL lower pulley and a small shot of n2o. the truck started missing a while back so i changed the spark plugs for him (NGK tr6) this seemed to help but did not solve all of the prob. He had the local ford dealership run a scan on it and they told him #1 coil was misfiring, we replaced the coil and it did'nt help. Now we are trying to figure out what is causing the misfiring, or whatever it is. My question is he ran some 116octane leaded gas in it before this started, is it possible for this to have hurt the injectors or anything else? Any help would be appreciated.
I have noticed the coils in ford tend to go out a couple at a time. You may want to have the other coils checked again. Also check the cats, Misfiring tends to let fuel gather in the exhaust and then backfire, then heating up the cats and damaging them.