Lean cruise was common in the 90's on GM cars especially. If you've ever heard a 1993 lumina euro with the 3.1L you know what I'm taking about. Lean running, tuned properly, is a great way to increase MPG. Under stead-state you don't have to worry too much about detonation and the combustion is hot and clean. You can thank our idiots at the EPA for making this 'wrong.'
Lean running is hotter and more complete combustion which is more efficient (key word, efficient). When oil companies and tree huggers are in your pockets, you phase this out because it creates higher NOX. The new thinking is lower NOX which equates to higher CO and CO2, plus uses more fuel to do the same work because unburned fuel is used to keep the catalyst hot for post combustion.......if you follow the money, you see why emissions standards and mpg don't get along. There is SO much technology available in Newer vehicles (gas or diesel) to drastically improve efficiency.
But, tuning for optimum efficiency doesn't sell more oil......or DEF. It's funny all the talk about CO2 emissions, they exacerbated the problem all by themselves.
BTW you are correct about the dream meter being off after tuning. I always do the math instead.
I remember the 7730 ecm running $8D in the 90-92 camaro and firebirds had a complete lean burn written into the bin. just wasn't activated. story was told gm wrote it, it worked well but epa said nope it could damage the emissions system (cat) so it was clicked off.
once accessed it was a easy bit to flip and turn on. I've seen it in action. it worked flawlessly.. get up above the set rpm, and below the load point. it would go to 16:1 airfuel and like 60deg timing. Calc mpg would jump from 25 to 30. and once every 10 sec or so it would flip back to 14.7 to service the cat and check its math since it only had a narrow band o2 factory. I had a wide band installed so could watch it work. was seamless, couldn't feel a thing as it flipped back and forth.
that was such a good driving code for it's time. I just struggled horriblly tuning hot restarts with it, since it didn't use intake air temp but manifold temp plus time air spent in the intake. I moved on to a different code that was easier to tune, os from the sy/ty guys did a crazy amount of mods to but didn't have lean burn on it. always missed it. years later someone else went thru the bin file on a hex level and realized they had missed an inverse sign in the code making it even more difficult to tune the manifold air temp conversation correctly. always wished I still had the car and setup to retest it after that.
ahh the fun times following along with the smart people defining and hacking the obd1 ecm's. it's a shame nothing is being done with the newer gm stuff. just pay the company and take what you get.
a buddy is into the vw world. those guys are still doing wonderful things with the new cars. fully defined ecm, able to add patches to the code for new fiction and even have their bcm defined and mapped to make changes to how the abs and traction control works around corners. all lost in the democratic world of omg don't mod anything in the bcm or you'll kill us all. lol.
anyways... I don't believe lean cruise would do much for our trucks with the crazy bad aero. the engine load is to high at 70mph to run truly lean. you might get 15:1 out of it, but to run 16-17:1 on today's e10 87 octane crap fuel, you'd need very very low load, a lot of timing and maybe even egr which don't think anything since the first Gen ls1s in the late 90s had?
if you could patch these ecm's to run a wideband, you could probably tune it a bit leaner at like 30mph low load cruise around town.
