I get the "temperature excursion exceeded 15.0C" message.

M143 returns:
Temperature limit for heater 1 is 330.0C

Thats a pretty wide margin.

Thanks for replying. I tried setting D to 4, still get a fault at about the same time. Curve looks stable.
Just to clearify, this is without any fan at the nozzle/heat block. Any other suggestions?

I am seeing theese spurious temperature faults. First I started getting them after installing a fan for printing PLA but limiting the fan speed resolved that.

Now I am getting them again when printing nylon at 260C (no fan). I have autotuned the PID regulator to 270C.
The resulting PID paramters I am using is M307 H1 A383.6 C190.7 D7 B0. Do theese look sane?

The termistor is configured as M305 P1 T100000 B4388 R4700 H0 L0 and is supposed to be a Semitec 104GT2 thermistor from e3d (I am pretty sure it is since I got it from a reutable vendor).

I have tried to change the fault time to 20s , M570 H1 P20 T15, but I still get faults and I dont really want to go further.

One interesting thing is that it pretty much always happens at the same time. All the failed objects look the same. It is after switching from infill to a printing a top layer. On the other hand I have tried extruding as much as possible and watching the temperature and it does not drop more than 5C ever.

Any idea what to try? Do I need a thermocoupler? A better thermistor?

All help is greatly appreciated!