check the burst disc.
If you still have the original moisture/oil separator make sure that the Oring is compressed. Mine came loose and I lost pressure.
Poster stated that it had issued but looked fine. this is NOT Fine and is caused improper oil!The piston rings were even worse. Carbon acts as an abrasive destroying the ring seal, which allows back pressure in the crank case . Exactly what your are experiencing. It is getting a bit old having members tell others that standard oil is fine, yet we see this issue almas daily on the compressor section of the forum. GRRRRR!!!Why oh why will members not pay attention? Really?Knife