Does low oil pressure cause fuel to burn lean?

I had to replace my motor a year ago. I got a used engine. From the beginning the check
engine lights comes on after about 40 miles. The oil pressure when hot idles at 10 ksi,
when running on 8 cylinders is at 30 ksi and when goes to 4 cylinders goes to 50 ksi. I
had to replace my catalytic converter twice since I got the engine. Other than that it runs
very good.

Took to the dealer first they replaced all O2 sensors, then the ECM. Charged me $10k
and did fix anything Finally they said  what is causing it is the low oil pressure due to ithe
emission is controlled by the oil pressure. They said the engine is going bad. I have put
25k miles on the engine and no problem and it still runs fine.

The shop that replaced the engine said the dealer are idiots and it a computer issue.

Any suggestions of the problem would be very much appreciated