Gas Mileage '93 Roadmaster

After changing the engine on my '93 Wagon to a remanufactured engine--new pistons, bearings, valve grind, cam, etc., a few items needed attention that caused the "Service Engine Soon" light to come on. Needed a new O2 sensor. Knock sensor was not hooked up, so I did that. Oil pressure gauge showed near zero pressure at idle hot, so I changed the sending unit which fixed that problem. I now have 20+ psi at hot idle and 40+ psi on the highway.

Now, with 5000 miles on the new engine, gas mileage still does not equal the old engine. What was 19-21 mpg overall country/city driving is now 15-17 mpg. 365 mile highway trip this weekend yielded 19.7 mpg. Same trip with the old engine was 23-25 mpg.

Has anyone tried ignition timing tweaks with this engine? The specs say to set it to 0 degrees with advance disconnected. Will a little advance make any difference, or is the computer going to retard timing to zero again?

Any ideas?

No one responded to the OP, so I'll update you about status. I set initial advance to 6 degrees instead of 0. Now, mileage is about 18 overall, with up to 21.7 on the highway only. Still not 25 like the original engine, but getting closer. I'm going to try 8-9 degrees initial advance to see if this works.