Good day Picers!

I have layout an easy LED blink circtuit at 4Mhz.
I only have 20Mhz PICs, 1 x PIC16F877-20l/P and 2 x PIC16F877-20/P

When I program the PIC16F877-20l/P @ 4Mhz it works fine, but when I program the PIC16F877-20/P it does not work and it's exactly the same circuit.

Is there any setting to get this Pics working @ 4Mhz?


Thank you!
Koossa