Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Skipping, shaking engine after changing spark plugs 04 Explorer v6

Hey I just changed my spark plugs the other day and since then my engine is hard idling and skips and jumps while I’m driving it. I’m being told I either need to change the spark plug wires or the coil packs. So my question is which do I need to change? And is there anyway to test which one I need to replace?


Are the wires original? If they are 5 years old or more, I’d change them first. Odds are that that’s the problem.

Other possibilities are: wrong plugs, wires crossed.

195,000 and the wires aren’t crossed and I made sure I got the right plugs matching with the old ones and I just purchased the car a couple months ago

Have you checked the OBDII system for stored fault codes?
Did you inspect the clip ends on the plug wires before reconnecting them? Are you sure they’re properly seated?

I once had a problem with seemingly good new spark plug wires failing. When the clips on the wire ends were opening to clip onto the plugs, they were opening up the crimps that held them to the wires, creating intermittent lack of circuit completion. That one was a stinker to find. It took some benchtop experimenting. I pass it on as a suggestion to carefully check yours.

I recently bought a set of NGK plugs & in less than 20 miles # 2 went dead , replaced that plug & all’s been fine since . Maybe you got a bad plug .

Sloepoke brought up a good point. What type of plugs did you install?
How do you know that the ones that were in there (that you matched) were correct?
Did you check them against the manufacturer’s recommendation?

my bet is one of the coils is bad. Happened when you unplugged it re-connected it. Purchase ONE new coil and try it on each of the spark plugs. No need to replace all of them.

COP can be fragile but always go with OEM plugs due to stories like this.

The bad plug I got was oem .

Autolite. And I checked online for my make and model I did auto zone and I took one out and went around a few mechanic shops seeing a what would be the factory equivalent

This is your engine, right? I’d triple check that the wires are connected correctly, then I’d replace the wires.

1 Like

More than likely you didn’t get the wire snapped onto the plug properly.

1 Like

Reading out the diagnostic codes would probably be the quickest way to get to the bottom of this. It worked fine before replacing the plugs, and that’s all you did, replace the plugs? hm mm m… it sounds like it has developed a miss, probably on just one cylinder. Here’s some ideas anyway

  • Spark plug faulty, or damaged during install, ceramic has a crack in it. Code would tell you which cylinder to check first. But you may have to remove all the plugs and carefully inspect them on the bench, with a magnifying glass for small cracks in the ceramic.

  • Plug gap incorrect

  • Plug not seated properly, cross threaded possibly

  • Sometimes the plugs come with a screw on gadget on the top which you have to remove in some installs to match up with the wire’s connector.

  • Likewise, some come w/a gasket and you have to remove that on some installs maybe. Double check the new plug configuration to the old plugs.

  • The coils or wires may have been about to give up the ghost, and just moving them around pushed them over the edge. Again, the diagnostic code would probably help.

If I had tis problem I’d connect up m o’scope to each wire, one at a time, using an inductive pickup, to try to see if it was just one plug misbehaving. Without an o’scope, on some vehicle you can remove a wire to see if the idle gets worse or better, not sure if possible on yours.

If you want to take a flyer, replace all the plugs, wires, and coils. I expect that will probably fix it. If not, at least you’ll have a spare set. Or reinstall the old set, might provide a clue.