[vncj96]

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.

 

[kennythewelder]

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.

 

[vncj96]

I literally just checked them all everything is right and I still have no CEL/DTC or freeze frame data on my scanner showing any issues

 

[kennythewelder]

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.

 

[RayVoy]

Any chance the wires are now mixed up after the last repair?
If you had more than one wire off perhaps they are crossed.

 

[xPosTech]

If it's cold at night where you are a neighborhood cat might have got under the hood looking for warmth. He might have been all over the engine so take a look for anything else he might have disturbed.

I guess it's possible 6 miles was enough to affect the learned tune offsets but not very likely. You can try disconnecting the battery to zero those out.

Ted

 

[RayVoy]

Haha, I've had 2 cats get into engine compartments, both were ours, both had fan damage and shorter tails.

 

[kennythewelder]

My cat just gaurds my Toyota, but it is warm here, most of the time.

 

[RayVoy]

Both times it was summer, not cold at all, I think it just seemed like a safe place to catch a nap.

With this truck, I'm always checking for where the cat might be, the spare battery shelf would make a great cat bed.