on my 98 buick century code p1441 comes up

Hi there, I have a 98 buick and I had the engine replaced with a (same size 3.1) 1999 engine. runs pretty good, but the check engine light comes on. even when I disconect the neg on the bat. the code p1441 comes up. when I start the engine after resetting the codes the engine light comes on instantly. I replaced the perge valve, new gas cap, filled the tank with gas,. looked over the hoses, and it also gets very bad gas milage After the mechanic put in the engine I tested it and the light was not on for about 3 days. any ideas? thank you , Robert