My K1500 DD Tow Pig

[L31MaxExpress]

I got to reading and saw the same thing with the MAP readings, so to get any better I'd need to log for that in and out of lean cruise on the same stretch of road to find out what makes it happiest. Looking at where it's 17:1 and leaner it's where I barely have the throttle cracked going downhill, so very low threat there. Flat roads are scarce near the house to get a feel for 70-80 mph, but I figured if I dragged it out at too high a load I'd just be shooting myself in the foot. I have a 1300mi one way/2600mi round trip road trip coming up next Saturday. If the wind isn't blowing like a sunofabitch I'll be able to get a good idea for the change in highway economy. Makes me want to try it on the Z06, but I think it'll kill cruise control if I do it. Worth a shot though as it's totally reversible. That gets 25+ mpg highway, 30 would be pretty sweet. I saw 31 on a trip to Denver and back. I don't know what it is about that stretch of interstate, everything I own gets freakishly good mpg on it.

I know this may seem goofy, but does that section of road have moderate rolling hills? Everything I own even without lean cruise gets freakishly good fuel mileage on roads that have rolling hills as long as there is not a large total elevation change. The hyper miler guys use a technique called pulse and glide. Where they accelerate and then coast then rinse and repeat. They claim better mileage doing it. I think the rolling hills have the same effect. The engine operates more efficiently climbing because it is not fighting the parasitic loss of the vacuum throttling the engine, then when you go down hill the engine practically freewheels and there are times DFCO even activates at highway speed.The heavier the vehicle the more noticeable this effect. I noticed this even with a stock Q-Jet fed engine. In over-run conditions with minimal throttle the carb actually lean cruised to a certain extent. I have actually read alot of their experiments on EcoModder.

FWIW, slightly modifying my driving style on those rolling hills also increased my mileage more. Rolling downhill, I pickup ~5 mph, then using steady throttle let the uphill section munch down the mph a little, near the top of the grade, let off a little so that the momentum is still carrying you over the grade and let the downhill slope lightly accelerate you again. Lets say I am in an area with minimal traffic and the speed limit is 75 mph. On flat land I hold the throttle steady at 70 mph, holding the throttle steady going uphill it munches down to 65 mph, then going downhill it climbs to 75.

 

[Supercharged111]

Lots of rolling hills, yes, but also a 1000' elevation change (but we're also high enough to realize aero gains). Our vehicles have enough muscle to climb the hills without downshifting, save for 1 or 2 in the Envoy. Likely some truth to your theory. I suppose that's how EGR is also supposed to help with mpg by adding throttle angle (even though that's not its primary purpose), but I never saw a difference when I deleted it.

 

[L31MaxExpress]

Lots of rolling hills, yes, but also a 1000' elevation change (but we're also high enough to realize aero gains). Our vehicles have enough muscle to climb the hills without downshifting, save for 1 or 2 in the Envoy. Likely some truth to your theory. I suppose that's how EGR is also supposed to help with mpg by adding throttle angle (even though that's not its primary purpose), but I never saw a difference when I deleted it.

The problem with the Vortec EGR atleast in stock form is it has very little flow at low engine loads. It flows at high loads when the engine would otherwise have the highest NOx emissions. Therefore it does not appreciably benifit MPG.

 

[RDF1]

I call it lean cruise but I run COS3 And COS5 in most my trucks so I use B3647 table to command what AFR at what RPM/MAP then use the high octane table to do all the timing. I'll send you some my tunes.

 

[Supercharged111]

You running semi-open loop? I'd forgotten about that until I flicked on lean cruise, then felt kinda dumb. COS3 doesn't have the RPM MAP table that COS5 does. I've been really scratching my head since going MAF only as the cold starts suck and there was no ECT modifier left as COS5 eliminates that. . . only it doesn't. They do give you a 2D table to add fuel based on ECT.

 

[RDF1]

COS3 has B3647. I ran OLSD on a few of my trucks and they did good. I towed with one of them through several states often and temps/altitude didnt affect the AFR like everyone claimed.

 

[RDF1]

12212156 OS to 2020003 COS3

THose are default data in the tables so dont go by those numbers haha..

 

[Supercharged111]

12212156 OS to 2020003 COS3

I have those on 12212156 gone COS5. My COS3 is based on a different OS though, maybe that's why. Semi open loop is cool, it uses STFT only but speed density and MAF using B3647. My MAF is dialed in pretty good, but the VE needs more cleanup so running without it right now. I may give semi-open loop a shot, gotta see if it's worth it. It would allow me to start a transition in boost off of stoich before jumping right to PE mode. Not sure if it'd break lean cruise, but if it did all I'd need to do is is recreate it in B3647.

 

[Supercharged111]

Today I logged airflow at idle in gm/s vs RPM. I'd been suspecting desired airflow was off and never had any luck with the RAFIG/RAFPN process. Turns out desired airflow wasn't that far off. I need to repeat that in gear to sanity check that table as well. Concurrently I had added some fuel to A0008 which is a 2D AFR adder based on ECT. I'd gotten pretty close just watching the wideband and making a mental note of the ambient temp. This time I used the scan tool to tweak it even closer and extrapolate down to the colder ranges that I'll surely encounter in MI, which is where I'm headed Saturday. We shall see. Ever since I went MAF only the truck's quirks were all but gone. That is, until winter came, and I was still left with unhappy lean cold starts. Since I knew the MAF was set up properly, I could then head down this path to hopefully make the right corrections without causing other problems. Time to live with it some more and continue to characterize its behavior. Same with the lean cruise.

 

[RDF1]

Ive had several issues going MAF only with the older PCMs. it works good with the E38 ECMs tho.
I stuck with OLSD for years and it seems to be the easiest way to tune for me.
I spent 6 days in the Holley EFI training school and now i just want to put a Holley ECU on everything. Ordered a couple Dominator ECUs for some my trucks to really have some fun.