Ihave been running a HEI in my 400 for years and not had a problem. This year, when under full load at around 4000 RPM it breaks down badly. I have checked all the wiring etc. appears to be OK.
Has any one else had this problem. I'm thinking it could be the modual inside the distributor, but have never worked on one before. Any suggestions.

if it is popping it could be the pickup coil also could be the module they are not hard to replace also check your part store for a rebuilt one some times its not much more good luck

I have checked the module, and it checks out OK, however, I replaced it. This did not fix the problem.
So I am back where I started.

you need to ckeck the pickup coil it is on the bottom that will cause popping