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If you're going to try to implement lean cruise via other means (not HP Tuners or other commercial software), the concept is that you can only go lean when the engine is warmed up and under light load. You don't want to go lean during cold startup (we've seen how this works with E85 conversions) and higher load.


We considered using an EFIE (connects between the O2 sensor and the ECM to go lean), but again you don't want to do this during startup (many EFIE's DO have slowed initial startup) or during any kind of acceleration, AND you have no way to add additional spark and cam advance.


This leaves only a custom tune with hundreds of hours of logging and tweaking. Our Volterado team has 3 active tuners (10 members) and I was driving gas to work every day and driving countless logging runs (unnecessary miles logging/tweaking a tune). Did I mention I charge for free so can drive EV for free so any time spent on gas is out of pocket?

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More about my application. I daily drive a 1999 Toyota 4Runner with 5vz-fe engine (3.4L V6 DOHC). Because the Toyota ECU is "locked", I do not have an HP Tuners or similar option. Any tuning is done with piggybacks to spoof the ECU. My truck has wideband "Air Fuel Ratio Sensors", and therefore always knows exactly what the AFR is.


I have a piggyback made by Split Second called an Air/Fuel Ratio Calibrator. It reads MAP, and RPM, and allows you to alter the AFR Sensor's output to the ECU based on RPM and MAP conditions. Changing this AFR Sensor output allows the actual AFR to go leaner or richer at different RPMs and load ranges depending on what I want. At light load, and cruising RPMs (say between 1,000 and 2,000) I could command a lean AFR via piggyback. Below 1,000 RPMs I would leave the piggyback zeroed out so I'm not running lean at first startup.


How lean (on lambda scale) should I shoot for if running on straight E85? Is there any benefit to lean burn if I can't command timing?

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Hi Robb,


Mileage gains with lean cruise as we implemented it, were best at low rpms. So at highway speeds above 70 mph, it's difficult to go lean, so no gain. Overall it's good for at 2 to 4 mpg with our best gains achieved around 60 mph.


It's possible to use an EFIE to go lean, but you'd have to have some way of switching it off via a vacuum switch & coolant temp or similar tech. (Low vacuum means higher engine load so turn off the lean.) But again, you need a LOT more spark/cam advance when lean or you won't get any power. Without the additional spark and cam overlap, you could only go slightly lean, maybe around 3-5%, certainly not the 20:1 we were doing.


To make matters worse, E85 burns slower and likes even more spark advance, which makes lean cruise even more difficult with that fuel.


TBH, you can't implement this without a custom tune. If you were going to do this yourself, assuming you knew what you were doing, and HP Tuners software costs $500, making it difficult to recoup your costs. We were only able to do this because of a team effort and one of us (not me) is a tuning savant and a year of logging by multiple people. Our biggest obstacle was the Chevy Volt isn't a conventional vehicle.


You might want to consider a different vehicle.


I had a '99 4Runner SR5 and loved it.



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