To be honest I wouldn't know how to grow a jalapeno pepper plant that only produced 8 peppers. I guess you could mow it down after the first 8?
That might stop it from producing more. Outside of that I am more interested in figuring out how it is possible to get so few? I am baffled.
Whatever you are doing just stop. Don't do anything. Only water when the plant droops completely, Never fertilize, Never baby them, Call them bad names, Kick sand in their faces and steal their girl friends and they will still produce more than 8 per plant.