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Thread: Tuning Prefrences...

  1. #1
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    Default Tuning Prefrences...

    Do you guys perfer OL or SD or OLSD ?????

    Please explain the differnce's between the 3.....

    Trying to decide which way I wanna go.... which way will be easier to control fueling (I.E. least tables possible to mess with....).

    THANKS
    01 Z06, 4L60E CONVERSION, L92/L76 TOP END, 72# LS3 INJECTORS (THANKS FIC), DRY NITROUS, COS5

  2. #2
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    First, the terminology:

    CL = Closed-Loop - in this mode, the PCM monitors the stock narrowband O2 sensors (which switch "high, low, high, low" as the AFR wobbles around stoich) and it continually adjusts fuel to stay near stoich.

    OL = Open-Loop - in this mode, the PCM ignores the stock narrowband O2 sensors and continually calculates correct fuel based on tables (and, if installed/functional, the MAF readings.)

    MAF = Mass Air Flow - this refers to the device in the air intake path that calculates the mass of the air entering the engine per unit time, based on the cooling effect the air has on a heated wire held in the airstream. The PCM uses this calculated mass to make adjustments to fuel based on the increase or decrease in air density (due to temperature, humidity, barometric pressure, elevation, etc.) The PCM only uses the MAF at low RPMs (under 4400, IIRC?), reverting to the tables above that.

    SD = Speed Density - this refers to the non-MAF method of determining the amount of incoming oxygen, which is then used to determine the proper amount of fuel to inject. The PCM enters SD mode when the MAF is not in service (removed, disabled, broken, etc.) or when the engine speed is high. In SD, the VE table is used to lookup the amount of air being consumed at a given combination of RPM & manifold air pressure (MAP.)


    OK, so what does this mean?

    Well, when stock, the car is in closed-loop operation with the MAF functional (CLMAF). This is generally a very safe mode because the PCM continually monitors the narrowbands and tries to make sure the car is neither too lean nor too rich (primarily for emissions purposes.)

    In order to really tune the car, however, most people (especially EFILive users) will disable the MAF and turn off the closed-loop mode, putting the car in open-loop speed density mode. This allows the VE table to be adjusted so that, for the atmospheric conditions at the moment, the PCM's tables can accurately determine the incoming airmass and correctly calculate the fuel to inject.

    Some people will, after tuning is complete, reactivate the MAF and re-enable closed-loop mode, allowing the PCM to make fueling adjustments based on the narrowband O2 sensors. As I mentioned before, this is sort of a "safe" mode but it is not the most efficient, leaving power on the table. Most people will leave the car in OL.

    The real question, for most people, is whether to reactivate the MAF or continue to run in speed density mode after tuning. The benefit of the MAF is the ability to adjust for changing conditions. The benefit of physically removing the MAF and running in SD only is that the MAF can be restrictive, reducing airflow slightly. In addition, the MAF's capability maxes out so folks making big power don't really have the MAF as an option. Plus the MAF is something of a complication that introduces another variable into the tuning equation and many choose to just eliminate it.

    Personally, with my limited mods and limited tuning knowledge/experience, I like OLMAF.

    Hope this helps!
    2004 Pontiac GTO - Quicksilver/red/m6
    1-of-344

  3. #3
    Joe (Moderator) joecar's Avatar
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    Just a quick note:

    For steady state throttle:
    If RPM is above B0120 (usually 4000 rpm), then PCM uses MAF;
    If RPM is below B0120, PCM uses combination of VE and MAF (transient->VE, steady state->MAF);

    EDIT by joecar: corrected post.

    If MAF fails: PCM uses VE if any of these DTC's show up: P0101, P0102, P0103; otherwise it uses "something else".

    Note: VE/MAF use is independent of open/closed loop (i.e. VE/MAF usage is "orthogonal" to loop mode).


    Last edited by joecar; May 30th, 2008 at 02:10 AM.

  4. #4
    Joe (Moderator) joecar's Avatar
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    This is all a bit tricky... so be sure to enable the throttle transients filter when tuning VE table or MAF table (actually, make the throttle transient filter very "strict").

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    Quote Originally Posted by joecar
    Just a quick note:

    For steady state throttle:
    If RPM is above B0120 (usually 4000 rpm), then PCM uses MAF;
    If RPM is below B0120, PCM uses combination of VE and MAF (transient->VE, steady state->MAF);

    EDIT by joecar: corrected post.

    If MAF fails: PCM uses VE if any of these DTC's show up: P0101-3; otherwise it uses "something else".
    Thanks, joecar! I stated that exactly backwards!!! (<scratches head> That'll teach me to read what I write... :( )

    I didn't know that about the "something else". Hadn't noticed {B0120}, either!

    EDIT: Wait! "...a combination of VE & MAF"? Now I'm confused. I thought the MAF acted as a modifier of the calculation from VE, sort of like an additional layer of correction. Are you saying that this is the way it works below {B0120} but that above that RPM it somehow ignores {B0101}? :???:
    Last edited by joecar; May 30th, 2008 at 02:10 AM.

  6. #6
    Joe (Moderator) joecar's Avatar
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    I get stuff backwards sometimes...

    I reread what I wrote, and I think I got right (but I am correctable if needed... ).

    The MAF is not a "modifier"...
    the MAF and VE both provide airmass values...
    the PCM decides which one it can "trust";

    Below B0120, PCM uses MAF if throttle is "steady" and MAF is "functional"; otherwise it uses VE.

    EDIT by joecar: corrected post.

    At higher RPM, the air flowing past the MAF is more "well behaved" (the valve event ripple amplitude becomes much smaller than the total airflow amplitude; I'm simplifying... there's a lot more to it which I don't yet fully grasp).
    Last edited by joecar; May 30th, 2008 at 02:12 AM.

  7. #7
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    Hmmm... <Wanders off deep in thought>

  8. #8
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    Terminology and Confusion, part 1

    Terminology and Confusion, part 2 (OLvsCL)

    remember there is no such things as pure MAF mode in these computers. you can kinda make it that way, but it doesnt work too well. if you're going with maf, you're tuning MAF and VE. you dont get to skip one part of it.

  9. #9
    Lifetime Member hquick's Avatar
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    Thanks for the info Marcin.
    I realy enjoy reading your write ups.
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  10. #10
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    Indeed! Thank you, Marcin. I had actually read those two articles of yours long ago but, obviously, they didn't stick. I'm now working my way through the other documentation you have on your website!

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