It's the crank sensor!
Join Date: Nov 2007
Location: Central Minnesota
I think that most of them nowadays are aluminum, but it is possible that both copper cores and aluminum cores are available. I've seen that with some other vehicles.
You could search an online parts store and see if it lists the construction material, but that still wouldn't confirm whether the one in your vehicle is copper or aluminum.
If you aren't sure, I would opt for something less aggressive like vinegar.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!