UPDATE: Any guys using the search to find out the diameter here it is:
On 98 3.0 2wd the pipe by the muffler is 2' and its the same after the muffler.
If your buying a after market muffler buy the 2 1/4 size and use the following if your doing it yourself:
2, 2.25" to 2" adapters
1, 2" to 2" muffler extension (you will have to cut down)
2, 2.25" clamps and 3, 2" clamps
This worked great and it sounds mean!! Heres the website I found the info on with pics, this explorer had the same setup as my 98:
I installing a new muffler today, I remember somebody telling me 2 1/4 was the size I needed. So I bought to 2 1/4 adapters and the new muffler was 2 1/4. Well after I cut the old muffler off I saw the adapters did not match up with the pipe but did work with the new muffler.
Im going back up to buy the correct stuff soon as sombody can correct me on the right size adapter to buy. Thanks
1998 3.0 2wd