Printhead on 3880 plugged when switching from PK to MK

I have never had a head plug completely. The printer was doing fine with PK. I printed a manual test pattern which had every dash in the right place. I then purged with piezoflush and got a perfect manual test pattern.

I switched to MK after replacing that cart with Piezoflush. Now my black position is totally blocked.

I Did several internet searches and have struck out so far on remedying this problem.

Can anyone help .?

Is the black position blocked for both MK and PK?

The 3880 has a problem where the MK/PK switch gets stuck. Check your carts too to see if one is empty.