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Thread: can a lean idle or going lean during light cruise harm the engine?

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    Default can a lean idle or going lean during light cruise harm the engine?

    Of course going too lean during wot can be really bad but can an extended lean idle or during light cruise harm the engine or will the engine just stumble if it goes really lean?

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    Quote Originally Posted by ryans1000 View Post
    Of course going too lean during wot can be really bad but can an extended lean idle or during light cruise harm the engine or will the engine just stumble if it goes really lean?
    GM lean cruise on some LS1's was around 16.5-16.8:1. Going any leaner they still run smooth at cruise but start to lose power. Really depends a lot on throttle/MAP.

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    Well it's not a yes or no question, it's a function of how much load and how
    lean. I run 16:1 up to 10%, 15:1 up to 20% and so on....

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    Quote Originally Posted by L31Sleeper View Post
    Well it's not a yes or no question, it's a function of how much load and how
    lean. I run 16:1 up to 10%, 15:1 up to 20% and so on....
    What tables are you using to do that? Table 3613 Normal PE Enable?

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    Short answer = no it will not hurt the engine AS LONG AS you are not trying to make significant power; once you move out of steady-state cruise and put your foot into it then ramp the AFR back to a safe level. What I was told, for best economy tune the VE table 'normally' (for best power) then after establishing the base VE lean out your cruise cells until the motor is down 5% on torque output. If you run the motor too lean then it will be so down on power you will have to bury your foot into the throttle and that will negate any economy gains, you can only lean out the motor so far until the strategy backfires on you.

    Mr. P.

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    thanks for the info!! i'm trying to autove and I keep running into lean cruises of 18:1 but i'm starting to get that sorted out. wasn't sure if I should pull over if I got stuck at 18:1 for a while.

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    Quote Originally Posted by ryans1000 View Post
    thanks for the info!! i'm trying to autove and I keep running into lean cruises of 18:1 but i'm starting to get that sorted out. wasn't sure if I should pull over if I got stuck at 18:1 for a while.
    It is worth keeping an eye on "Cat Temp" to get an idea of how the lean burn is affecting exhaust temperatures vs non lean cruise.

    If you D/L a Holden 2003 LS1 calibration from holdencrazy.com, and look at the lean cruise area, you will see what the factory deemed acceptable at that point in time with that engine at various airflow/RPM points.

    Be interesting to know if anyone here is aware of whether the "lean cruise" capability was an offset to running in closed loop, or whether the PCM switched to open loop for lean cruise.

    GM doesnt implement this anymore, so maybe the increased NOx emissions put paid to that idea that would have seen a reduction in CO2 emissions .

    Interesting point Mr P on the 5% reduction in torque number. Be interesting to know at what AFR/Lambda this reduction commences at.

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    Quote Originally Posted by gmh308 View Post
    ...
    Interesting point Mr P on the 5% reduction in torque number. Be interesting to know at what AFR/Lambda this reduction commences at.
    On a 2004 Chevy extended-cab truck with 5.3L, it's 15.4:1 AFR on gasoline (not E10 or gasahol); the observed highway mileage gain was 2.5-mpg; this was arrived at experimentally, we might not be entirely correct on our calibration and it would take a LOT of driving to really nail this down.

    Mr. P.

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    Quote Originally Posted by gmh308 View Post
    It is worth keeping an eye on "Cat Temp" to get an idea of how the lean burn is affecting exhaust temperatures vs non lean cruise.

    Is it the rear o2 sensor that measures 'cat temp' ?
    9.8@150 . LQ4 Turbonetics Billet 7575@18psi, 6 speed, non-intercooled with meth. Speed Density, open loop, no PE.

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    Quote Originally Posted by ryans1000 View Post
    Is it the rear o2 sensor that measures 'cat temp' ?
    Cat temps are estimated from the front O2 heaters.

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