I know this is an older thread (no pun intended) but using the suggestions and tips here, I have solved my FMQ problem on my Pfaff QE 4.0. : using Gutterman (sp) thread, I had bobbin thread showing on top and top thread showing on bottom and top thread was shredding. Still using same thread,
1. I put the thread on a metal stand behind my machine then threaded making sure I used the method shown to me by the dealer. (QE 4.0 sm are easy to not stay in the tension disks),
2. changed needle from a quilting 90/14 to a top stitch needle 90/14, which I learned from Mr. Bob and
3. changed the upper tension from default 4.6 to 3.0. I learned from doing the test someone recommended.
Thanks to the original poster and all of you who contributed the tips and you tube links.