Our 90 gets about 18-19 around town and has recorded 30 on the road with the a/c off. Looks like the SII engine gets about 20% more (from the LeSabres AVIS has given me with MPG on the dash).

TranSport usually does about 22-23 on the Interstate but is pushing more air.

On all the MPG is best in lockup o/d at 55-60 mph, 70 etc drops about 15 %. Suspect it may have something to do with the National 55 mph speed limit being repealed a decade ago and GM adjusting the "sweet spot".

88 Reatta does better around town probably because there are a lot of 45 mph zones and it gets into 4th/lockup then while the Bonne needs over 50 mph to stay locked (if gas gets much highter am going to adjust that, max mpg requires min rpm).

All could probably stand running a bit leaner at cruise but again I have not bothered yet.

Wonder when people are going to trade in all of those SUVs.

Ya well my TC doesn't lockup so that already hurts my mpg'*. But around town i'm pushing MAX 8-10 MPG. Totally ****. But hopefully after my CAI (sooner or later) and the O2 sensor It will get a little better.

Even without lockup, something is seriously wrong, even leadfooted around town you should get 16-18. Sounds like more than just an O2 sensor, time for a complete scan. while running at operating temperature.

Well i KNOW it'* running waaaay rich. I can smell it out of the tailpipe. I know i'm getting terrible mileage because driving around town for about an hour i can actually see the needle drop 3-4 of the smallest hash marks on the gauge. But the car seems to run fine, i only get the occasional sticky EGR code. But the whole thing is just odd. Idk anyone with a scantool around here, so i'm not sure how i could get any more information. I do know however that the car runs fairly cool, about the first notch above 100 or whatever it is on the gauge when i'm really driving hard. I pulled one of the plugs and checked it back when i had my transmission out and it looked like brand new and was perfectly gapped at .055. But i should really to a delco ignition swap sooner or later and get a CAI on it. But you do think that the O2 will make a large difference?

The 02 is a damn good place to start, and your sticky EGR could be a victim of the rich condition. With your TC not locking up, I suspect it may be slipping too much in normal driving as well. What'* your trans fluid look like?

And keep in mind, while running rich, you're fouling all your plugs. Take them out and clean them, or simply replace them. The Delco type2 ignition upgrade should also help you. I'd do the O2, ignition upgrade, and change the plugs all at once.

Also keep in mind, it may smell rich and get worse mileage due to a MISFIRE or intermittent constant misfires.

Any chance yor thermostat is stuck open or your coolant temp sensor is reading low ? Either one could be the reason it won't lock up (coolant must read above 146F) and are running too rich (do not come off cold enrichment until about 60C.- sorry for mixing dimentions but is how I know them.)

You will find that the calibration of 02'* vary from sensor to sensor. some leaner some richer.
I have two brand new single wire sensors still in the box. don't want to try them because the one on the car now gets good mileage. (similar to Padgett)

Well the TC isn't not locking up because of temperature, i tried manually locking it and it won't go. The solenoid is trash. Of course i don't know what temperature the car actually runs at because i can't scan it. I think i'll go ahead and get that O2 sensor, and remove all the plugs and check them out, as well as look at the wires. The tranny fluid is in perfect condition, bright red and smells good after a good 700 miles of hard driving (new tranny). And to correct myself the EGR isn't "sticky" per say, because i can move it by hand, but once in a while (better now) i get a code 32. The EGR is pretty new, it was done like 50k ago i think. I'd have to look at all the service records.