Effects Loop

I've heard that there was an effects loop mod. Wondering if you knew what my problem could be?
I tried to put a chorus pedal in the loop. It made a clean setting sound distorted.
I also tried it between my guitar & input with same results.
I've tried a couple different rack effects. But just haven't found one that I liked where the delay when changing patches on them was acceptable.
I was thinking ok, I'll try some pedals in the loop and see if I like that.
Is there a mod that changes components out to make the effects loop receive pedals?
Or I'm I just setting something up wrong?
 
Thanks,
Darrall