They ran fine throughout the RPM range, it's that they'd abruptly experience total failure rather early, in the midst of an otherwise perfectly good run.
I haven't run them in a few months in favor of going all-OS, I'd be willing to give them another shot just because I have them left.
My...
The problem I run into with HSP plugs is that they physically break. I've never found any reference to this failure mode for glow plugs. The center post would be loose, like I could wiggle it around with my finger, and even twist it and the coil on the other end would wind or unwind. The coil...