I have a Buick GN that uses the 148 ECM. Its pretty well unable to do anything but fixed C/L cruising. The factory PROM had code in place to enable O/L idle mixtures but its not really too smooth doing its transitioning, and they locked it out and used a full time C/L idle at 14.8:1. The GNs are well known for having a crappy idle. At highway speeds it just adds some timing under light load conditions. I wrote myself an O/L lean cruise patch that works pretty well.

I was wondering what happens with brand new cars. Do they use a rich idle and still meet emissions? How do they get cars to idle so smoothly? Many new cars get really good mileage on thehighway too, do they run lean mixtures?

 

I'm totally unfamiliar with the '148, so I can't make any comparisons, but I can tell you a bit about the newer ECMs.

For instance, the '7730 $8D mask.....there are simple ways to disable closed loop at idle, or eliminate closed loop altogether if you're the kind of guy that doesn't like the O2 messing with his tune. There's "highway mode" which serves the sole purpose of changing fueling and timing under light-throttle cruise to help increase gas mileage. There's "power enrichment" which invokes open loop under hard throttle to allow richer mixtures for more power. There are adjustments for how the O2 corrects fueling in closed loop, and there's the ability to using minor timing changes to help maintain a smooth idle.

That scratches the surface, and this is all with a relatively "old" ECM. It hasn't been used in a new car in 10 years. The really new stuff is even more complex.

 

Just set the O/L enable, hi, and run open loop. Thou you need to run a WB to verify where you are.

Trouble with most GN cals is they run way too much timing.

I've broken 30 MPG with mine, but it took being cruel to the motor to do it. Personally, I'd rather get 25 MPG and not be killing the rod bearings. 36d total timing, and ~13.6 seem to be a sweet point for mine.

There's a million reasons for lousy idles. With a 206/206 cam mine idles well. Not as smooth as some v8s but no v6 will be as smooth as a v8. Seems like some people want a v6 to idle like a v8.

More powerful processors, real time injector feedback loops, better ignitions, more refinement in all the mechanics over ~15 years takes it toll.

 

Don't forget better mounts! I KNOW the 2.4 4 cylinder idles pretty much as bad as the 2.3 Quad 4 predecessor, just you can't feel it as badly in any of the newer cars, because of the mounts! Don't be fooled into thinking ther really idle more smoothly!

 

I have a 97 Bonneville and I believe the 3800 has balance shafts which help a lot. Its odd, it must have a really loose torque converter, it idles at 900 RPM warm in gear and about 1000 RPM in neutral. Its smooth as silk. It also gets 35 mpg on the highway with my heavy foot which I think is really great but I was wondering if it runs lean or not in that mode.

 

New engines have resonance tuned engine mounts, resonance cancer growths on the intake tracks and cats RIGHT off of the manifold. Those 3 things alone will make an engine seem to idle like glass when infact chaos is a hands touch away.
Newer cars also have what I like to call "full potential" heads and designs that promote awesome quenching and ignition. This allows them to run leaner air fuel ratio's which lowers all emissions and get good milage. They're just better refined designs mechanically then they ever were thanks go computer simulations and expensive sound equipment. The better resolution tables in the computers also helps some but the better combustion chamber, cam, and intake designs are really the biggest difference. Just look at the "primative pushrod" LS1's where it only takes a cam swap to add 150hp and it still idles like a champ. The heads are so good it's hard for the aftermarket to compete anymore. Most of them have resorted to porting STOCK heads because they can't find any way to improve the overall design.

 

I like all the points you made. Are you also saying that they do not need to run lean, that they stsy at stoich all the time (except for power mode of course).

 

Most new engines will run stoich almost all the time to keep emissions ultra low at every vehicle speed/condition. Back when our ecms were made the engines were rather old designs that had no good computer modeling. Computers have rocketed engine design to an almost stagnant state. Swirl, tumble, quench, ignition, and compression has all been figured out in the past few years. Now it's all about manufacturing the cheapest possible "ultra clean" motor. The superior chamber designs allow for a much leaner (efficient) AFR to be burned. This means the engines run best at AFRs closer to stoich than every before. Basically the better the efficiency of the chamber/flow the closer to stoich the engine can be run. Turbo vehicles run with richer AFRs because the chamber is under more compression (fuel comes out of suspension). This is my feeling on why boosted cars like richer AFRs.
Any questions? See any flaws in my explinations?
Big block chevy 454 truck motor making only 220hp low compression terrible swirl and virtually no quench = 11:1 afr under WOT while a motorcycle 600cc 4-stroke has awesome quench and tumble = 13.6:1 afr. The cat converters have also gotten a lot stronger in the past few years. They're held to the metal with better materials and so auto manufacturers can reduce HC emissions under hard acceleration by running complicated (but usually low 13 afrs) routines to check and monitor cat temps. I dont' know for sure but I think it's safe too assume that new ecms have code that monitor the cat temps and adjust the AFR accordingly. Example; cruising down the highway and you punch it for power, cat is relatively cool so the ecm commands the afr that's best for power. If you're towing a boat and have been going up a hill and THEN want to pass (cat's rather hot) it'll run a rich afr to cool down the cat and then cycle the afr to keep the cat happy AND the car accelerating hard. It's all a matter of balancing emissions now, not power so much.