So i just changed my spark plugs as well as wires and i was getting around 17.5 around town and now im struggling to even break 15. they're bosch plugs, i double checked and they were pregapped. I was in a time crunch and so i ran a couple wires over the top of the engine; i don't think this would affect anything but figured i should state that. Any thoughts as to what would be causing this?

side note: we pulled our trailer to the beach for camping this weekend. when we were just pulling out of our camp site crawling at about 5 mph, it sounded like fire crackers were going off in the engine compartment. we stopped, opened the hood and the popping/cracking/snapping seemed to be coming from the spark plugs? it slowly disappeared and hasn't made the noise since. That was a new one for me. feel like my engine is about to give out on me!

 

If you heard cracking from the spark plug areas I would say either you don't have the plugs all the way in or something is arcing, like maybe your spark plug wires? Try running it at night or in a dark area and look for little lightning bolts.

 

the crackling happened for about a minute in duration and hasn't happened since. look for lightning bolts... in the plug wires? all plugs are tightened down...

 

Yes, if your plug wires are cracked then they could be arcing to a metal surface. This would cause what looks like a lightning bolt to jump from the plug wire to whatever surface it is jumping to.

 

I believe if you check the general consensus here is to replace the O.E. Spark plugs the the same exact ones. It's not that other brands of spark plugs aren't any good, it's that the originals are made to the specifications required by Jeep. Temperature they run, the power of the spark etc.

 

First of you should reroute the wires the correct way so that they don't get frayed or burned. Second make sure that all the wires are going to their respective cylinders correctly. The noise you are hearing is the wires arching which means that the spark is not making to the plug which results in all cylinders not firing which leads to your loss of MPG's. Just because you don't hear the arching doesn't mean its not happening.

Get a spray bottle with water and at night with the motor running spray the wires, coils, and plug area with the water. This will show exactly where the wires are arching. Also make sure the wire is pushed all the way over the plugs.

 

Or-lay one hand on the fender. And run your other hand down the sides of the wires.

 

That would be pretty funny, almost as funny as someone not waiting for nighttime and spending a little too much time in a closed garage with the motor running looking for bright lights.

 

My factory wires were arching from the coil to the a/c line a month after I bought the Jeep. Had to bend it farther away...

 

There is one more often overlooked scenario. Did you possibly drop or bang a plug during install? That ceramic is very brittle and a small crack in it will do exactly as you describe.....even if it is not arcing, you will lose power from that cylinder.