open loop

[BLeeBull]

Is it common to tune to always run in open loop? I am working on such a tune. During tuning i found my best economy on the interstate is with an a/f ratio of about 16.5:1-17:1 and the chassis dyno has me at best HP at a lean sounding 13.5. So far It has resulted in about 7mpg when running on the interstate at 70 mph vs my attached tune. 2nd thought, This seems like too much of an improvement.

with the attached tune in closed loop my wideband seemingly cycles rapidly between about 14.5 and 14.9 while at steady state cruise with terrible fuel econ (10 mpg). I think the WB verifies the NB sensors and tune are accurate, or at least they are in agreeance.

current open loop tune is 17 mpg at an average of 16.8:1 at 70 mph.

engine: 6.0 LQ9, TBSS intake, 1 3/4 longs, 218/223 113 cam at 110 icl
1996 OBS chevy 4;10 gears 29.25 tire. about 2500 RPM at cruise.

2 new NB sensors and new WB

What is happening here? it seems like both my NB and WB are reading leaner than actual. There seems like no way could it be so bad when the wb shows right at 14.7, and no way it is that much better at around nearly 17:1.



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[5FDP]

What injector are those and in the injector data correct? Also are you still running the stock DBW stuff for this computer?

Running a lean burn at cruise can net better fuel mileage something is wrong if you can only pull 10mpg in closed loop at freeway speeds.

And the 13.5 AFR on the dyno may squeak out the best power but I'd never run a engine that lean on regular premium pump gas in a heavy truck. I'd still be in the 12's for a safe air fuel ratio.

I'd return the stoich to 14.68, make sure the injector data is right and redo the VE and MAF tables.

The timing tables need some work too. With how your idle timing and spark correction tables are set, it's probably a kinda choppy idle and the cruising timing could be higher based on what I see. With no data logs I can't see what it is doing.

[BLeeBull]

well one issue is I posted the file that cost me money. So here is the one it is running now that i messed with on the dyno. The injectors are a set of stock flex fuel 58lb. Sorry, here is what is loaded in the truck right now. It is an SD with stock DBW throttle body. This is tune actually did best on fuel mileage (17 on interstate and fuels good based on me glancing at the WB often and what I remember from the LTFT. Logs are on a laptop I am now having difficulty getting to boot up, but working on it. What bothers me is that I was messing with the truck the other day open loop tuning. Wife was driving, in RTT mode .we were rolling down a road that goes miles through the swamp. As i was leaning it out with cruise set at 65mph. When we got to about 16.5: 1 the truck sounded better and the fuel flow meter frequency dropped 15%. I will get you the log file when I can. It bothers me that leaning it out picked it up as much as it did, like I am not seeing something.. with this tune it idles almost stockish. The truck is Just a SWB 2wd so its not too heavy. Appreciate anything you see that's screwy.