The plug wire falling off won't make it go bad, but have you checked all of the plug wires on both sides to insure that none of them are loose ? A trick to find misfire in plug wires, is to check the plug wires at night, in the dark, with the engine running. If there is a misfire, you should be able to see it in the dark.
Spark plug wire fell off
My 99 5.7 K1500 started running like crap, 2 days ago. On the way home from work my CEL came on so I scanned it when I got home, misfire in cylinder 7. Went under the hood and the spark plug wire had come off the spark plug. The wires were new 16 months ago so not sure why all of a sudden I’m came off. It snapped on nice and tight and wasn’t lose.....BUT the truck is still running like crap. Nothing is showing up when I scan it. Should I assume that spark plug is crapped up now? Or could the wire be bad if it arched while it was popped off, it was only driven about 6 miles in this configuration mostly at 30mph.
Also I am getting backfires on deceleration.
Also I am getting backfires on deceleration.
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In the old days, we would take a pair on insulated pliers, and with the engine running, pull off each plug wire, one at a time then putting each back on, until we would find the one plug wire, that did not change the way the engine was running. If there is no difference when you pull off that plug wire, then that is where the misfire is. It is very easy to shock yourself doing this, so a rubber glove can help, but you can still get shocked. If you do proceed with this method, do this at your own risk, and be very careful.
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