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Thread: O2 Switchpoints for Fuel Economy

  1. #1
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    Default O2 Switchpoints for Fuel Economy

    Attempting to do some fuel economy tuning on my '01 Silverado 5.3L with a 212/212 114 LSA cam. I've upped the idle timing to increase vacuum and reduce fuel flow. And I've got DFCO set up pretty well.

    I was curious what you guys would recommend for O2 switchpoints? Mine are currently 450 mV across the board. I've seen some as slow at 300 mV.

    Does this essentially "trick" the PCM into thinking that it's running at stoich when in reality it's running a bit lean? Should I avoid changing the switchpoints if I were to enable lean cruise?

    Thanks!
    2001 Silverado 5.3L ECSB 2WD T56:
    T76 turbo, Meth injection, 72# injectors, 799 heads, 212/212 114LSA cam, Built 4L80E, 3.42's
    EFILive V1 Commercial, COS5 2-bar SOLSD, AEM wideband

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    Default O2 Switchpoints for Fuel Economy

    Subscribing. Hopefully will be going down a similar path with my 05 5.3 I just bought
    14 GMC Sierra
    5.3L CC SB 4x4
    Basic tuning....

  3. #3
    Lifetime Member Gregs's Avatar
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    Quote Originally Posted by ferocity02 View Post
    Attempting to do some fuel economy tuning on my '01 Silverado 5.3L with a 212/212 114 LSA cam. I've upped the idle timing to increase vacuum and reduce fuel flow. And I've got DFCO set up pretty well.

    I was curious what you guys would recommend for O2 switchpoints? Mine are currently 450 mV across the board. I've seen some as slow at 300 mV.

    Does this essentially "trick" the PCM into thinking that it's running at stoich when in reality it's running a bit lean? Should I avoid changing the switchpoints if I were to enable lean cruise?

    Thanks!

    I played around with it a few years ago but found that its not a good idea. Its best to keep them all at .450. Changing switchpoints is like hacktuning, you end up with something with worse drivability. Its better to be honest with the pcm and just use the leancruise tables to tell it how to run. You'll avoid the drivability problems that you would otherwise create.

    I get frustrated with everyone wanting to change switchpoints... but I do understand how it started. Everyone got all excited abut this stuff when the users of "another tuning software" decided it would be a great idea to not actually TUNE their vehicles but TRICK them... End of rant

    03 Silverado 5.3 ECSB 4x4 Z71
    Intake, Exhaust, Vette Servo
    285/75/16 tires, 3" Body Lift
    Comp Cam 206/212 .515/.522 112 lSA, hardened rods with LS9 springs
    Lots of Ham Radio equipment

  4. #4
    Lifetime Member EagleMark's Avatar
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    Quote Originally Posted by ferocity02 View Post
    Should I avoid changing the switchpoints if I were to enable lean cruise?

    Thanks!
    I'd say to watch it anyway? I've tried this on a limited bias, no MPG tests, just watching AFR via Lambda. From changing overall .451 to .750 saw a change from .100 Lambda to .98. The other way, leaner from .451 to .250 only went to 1.1 Lambda. So I did not see results that were outlined in this thread.
    http://forum.efilive.com/showthread....itching-points

    There's another couple O2 Paremeters that would help the switch point and may be the reason some OS work better then others. O2 high and O2 low. When you couple these to the switch point you can see it works well!


    Quote Originally Posted by ferocity02 View Post
    And I've got DFCO set up pretty well.
    Have you got DFCO to work below 40 MPH? I've got a different OS and there's no Parameter for this so I'm stuck, could easily go to 25 MPH or less when exiting freeway.

    I've asked to add these or give info to their location but no luck? I think EFI Live is leagally worried to release anything that can be found to effect emissions, except when covered by the vehicle being for race/off road. They are even removing some high profile diesel legal issues in next release.

    There is a disassembly available for the 2001 OS and may be able to find these parameters, we'd have to wait for one to be released for 2002 OS...
    http://www.gearhead-efi.com/Fuel-Inj...S1-PCM-Project!

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    Quote Originally Posted by EagleMark View Post
    Have you got DFCO to work below 40 MPH? I've got a different OS and there's no Parameter for this so I'm stuck, could easily go to 25 MPH or less when exiting freeway.

    I've asked to add these or give info to their location but no luck? I think EFI Live is leagally worried to release anything that can be found to effect emissions, except when covered by the vehicle being for race/off road. They are even removing some high profile diesel legal issues in next release.

    There is a disassembly available for the 2001 OS and may be able to find these parameters, we'd have to wait for one to be released for 2002 OS...
    http://www.gearhead-efi.com/Fuel-Inj...S1-PCM-Project!
    I'm using 12212156 and it has a MPH enable setting, mine is currently stock at 15mph. It works perfectly, and honestly the DFCO is probably the most reliable thing in my tune, very predictable. What OS are you running?
    2001 Silverado 5.3L ECSB 2WD T56:
    T76 turbo, Meth injection, 72# injectors, 799 heads, 212/212 114LSA cam, Built 4L80E, 3.42's
    EFILive V1 Commercial, COS5 2-bar SOLSD, AEM wideband

  6. #6
    Lifetime Member EagleMark's Avatar
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    Same OS. But there is no Disable MPH, mine kicks off around 40 MPH from highway speeds.

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    Have you adjusted the enable/disable RPM and MAP? My RPM enable/disable are now 1500/1000 for all gears. Not sure what my MAP enable/disable is, but I had to raise it up slightly because of the cam making less vacuum. I may disable the MAP settings so it only works by RPM.
    2001 Silverado 5.3L ECSB 2WD T56:
    T76 turbo, Meth injection, 72# injectors, 799 heads, 212/212 114LSA cam, Built 4L80E, 3.42's
    EFILive V1 Commercial, COS5 2-bar SOLSD, AEM wideband

  8. #8
    Lifetime Member EagleMark's Avatar
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    Yup! Played with them a lot to prove the MPH Disable setting.

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    Quote Originally Posted by EagleMark View Post
    Yup! Played with them a lot to prove the MPH Disable setting.
    Is yours an auto? If so then there might be some other settings involved causing DFCO to disengage early, like TCC.

    Mine is a T56 so DFCO is pretty straightforward to setup.
    2001 Silverado 5.3L ECSB 2WD T56:
    T76 turbo, Meth injection, 72# injectors, 799 heads, 212/212 114LSA cam, Built 4L80E, 3.42's
    EFILive V1 Commercial, COS5 2-bar SOLSD, AEM wideband

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