OK Joseph. More Q/A... With that many miles, rebuilt engine, how old are the cat's, and other parts? O2's are these original, aftermarket, or? I'll guess you and 4WD Bill have closely compared notes, example you know differences in the EGR's operating threshold. You could temporarily disable EGR and test results. Have you pulled the EGR itself to see if it's clogged w/ carbon or sticking open? Tested it w/ a hand vac. pump? Do the Calif. and Fed. spec Civic's use the same part# EGR? If same part#, is the intake man. same, or differences in the EGr passages? If everything is the same parts-wise, then the diff. is in how or when the ECU turns on the vacuum actuation to the EGR.?? Does the EGR vacuum circuit go thru a water temp TVS switch? Might this TVS have a different temp setpoint? Or does the EGR vacuum circuit go thru a computer-controlled solonoid switch? If all the EGR system's parts are same, then diff. is in the computer itself?
Or try a restriction in vacuum to the EGR, a hose connector w/ a smaller ID hole in it spliced into the vac. hose, as a test. Parts stores and junkyards a source for dinky parts like this. You would just have to try these ideas, and see what happens. How fussy the ECU might be, since if EGR doesn't open as much or as soon as stock, it's got that EGR position feedback sensor on top of it. If the EGR IS the real problem,and no problem with the EGR itself then it could involve delaying/reducing it's operation. Might need to research the EGR sensor on top, what it's output signal is, find which wire is output signal wire, how to modify it. From looking at the Rock Auto pic, EGR is opened by the vac. signal, and the output sensor on top is prob. a voltage-dividing potentiometer that has varied output back to ECU as feedback. It has 3 wires that's a clue right there. I don't know if disabling/tweaking the EGR would cause ECU to go into limp/default mode w/ accompanying bad MPG.
Other sensors, MAF, or MAP, ignition, temp, or whatever, any issues or info on those? Seems kinda counter-intuitive that a Calif. spec Honda would do better than a Federal spec one?? I'm not intimately familiar w/ Honda's, I did work on an '84 CRX a lot years ago, I admire Honda's in general.
Those are impressive MPG's on both Civic's you guys own despite Bill's ride doing better.
What about some other g-Man "tricks", tire press, MPG Remedy, Ozone dist. cap, fuel heating, synth. oil/lube's, anything to increase power or decrease losses? PCV re-route, Idle air re-route/restriction...? I can't recall all about what you and Bill have previously posted here. Whatever the issue is, there IS a reason/reasons for the results, I for one would like to see more in-depth info re: both of these Honda's. Honda's are enormously popular. Everyone here can benefit if we re-visit the Honda "bag"! Pics, we need more pics, AND info!
Do please tell more about these Pocket Rockets! (Tracy pants like a dog waiting for his treat...)
Tracy G