Swap a 3.1 for a 4 cylinder in a 1992 Lumina?

Hello group.

This is my first post. I own a 1992 Lumina with the dreaded Methanol variable fuel option. But, I have grown attached emotionally to the car and the body/interior is in "pristine" condition. About 35,000 miles ago, I had the engine, a 3.1, overhauled but am experiencing rather bad gas mileage and sundry SES errors and the car "bolts and bucks" at times, the methanol sensor will indicate 10% and then 42% rapidly back and forth as a pre-indicator that the car will not run well at times, then, miraculously, the indicator resets back to 0% or just 1%. I have had it with this engine. I really like this car and want to ask this group what parts would I have to replace on this vehicle in order to "downgrade" it to a 4 cylinder engine? It is an automatic trans. with "overdrive" on the shift column as a selection. The main reason for my question is that the gas mileage is intolerable (about 15 mpg). Can this thing be done? Is it easily "doable?". What about the previous "methanol sensors, ECM, etc." How would I go about "upgrading" those?
Please excuse my ignorance in general, I do not pretend to be a mechanic, but rather a person who pays to get things done. Thanks you for any advice you can offer.

Jack.

You are opening a can of worms there. There is so many people here having huge problems with v6 to v6 swaps on normal fuel systems, I can't see any good coming from what you are proposing. I am not familiar with any of the swing-fuel systems you have. I do know that the manufacturer is responsible for 100,000 miles on a standard model for any issues that effect emissions, regardless of time elapsed. I would guess there would be that or more on the system you have. If nothing else, I would think it would be easier to convert it to gas-only operation, and have any issues with the engine control fixed after that. My '97 3.1L Lumina gets about 29 hwy and 21 city, BTW. The lumina is not a small or light car, and a four would have to struggle to move it effectively. I think the higher throttle opening required to get it moving from a stop would negate any city driving mileage gain from having a smaller engine. Highway mileage on open, flat highway would probably be better, though.

Just noticed that you live in Cali. You can't legally swap motors other than like for like, and can't alter the vehicle's O.E. emissions or engine control legally. I wish I could get a look at it. I haven't had the opportunity to see the swing fuel system for real.

I was just thinking, from what I remeber of that system from reading, it measures fuel ratio by measuring resistance across a sample volume of the fuel in the tank? If so, the wild readings you describe would indicate a malfuction or ground loss at that sensor perhaps? If I knew where that sensor or probe was, I'd start by checking its' harness and ground.