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Thread: Closed Loop vs. Learn Enabled

  1. #1

    Default Closed Loop vs. Learn Enabled

    Rookie questions. I understand Learn cannot happen unless Closed Loop is enabled. Reading through the help sections and I'm still not entirely clear about the following:

    1. If I have Closed Loop enabled AND Learn enabled - the system continually adjusts the Learn Table and applies that correction to the Base Fuel Table to maintain the Target AFR correct?
    2. If I only have Closed Loop enabled BUT NOT Learn enabled - does the system continually adjust to meet the Base Fuel Table and no Learn Table correction is utilized?

    Trying to understand if I have to shut down the O2 for some reason (for example maybe it shorted out due to condensation and reads full lean) what are the above toggles doing and what might my options be to get home under my own power until I can replace the O2. Thanks!

  2. #2
    Join Date
    Dec 2009
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    Connecticut
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    Quote Originally Posted by rvander68 View Post
    1. If I have Closed Loop enabled AND Learn enabled - the system continually adjusts the Learn Table and applies that correction to the Base Fuel Table to maintain the Target AFR, correct?
    YES. Additional notes below (a "copy & paste"):

    Learning happens at all RPM, provided the Learn Parameters are programmed as such.
    Is the Coolant Temperature Enrichment % or A/F Ratio Offset still active? These must be at 100% & zero to enter Learn mode.
    You may need to reconfigure these tables if you're running the engine colder than what the base calibration specifies.

    Closed Loop & Learning isn't active during periods of acceleration enrichment or deceleration (zero TPS, 400 RPM above target idle).
    The engine needs to be at "steady-state" RPM for the Learning to function, at lower RPM.
    The Closed Loop Status has many momentary periods when it's inactive (Open Loop mode).
    This is normal due to the TPS & MAP based acceleration enrichment (transient fueling).
    Also, any "noise" on the TPS or MAP signal wire (false Rate of Change) will deactivate Closed Loop.
    https://www.holley.com/document/tech...__statuses.pdf (Sensor Diagnostics & Statuses)

    2. If I only have Closed Loop enabled BUT NOT Learn enabled - does the system continually adjust to meet the Base Fuel Table and no Learn Table correction is utilized?
    This scenario will still operate in Closed Loop to correct the air/fuel ratio in accordance to the Target A/F Ratio Table.
    However, the Learn Table won't modify the Base Fuel Table, so Closed Loop may take slightly longer to happen.

    Trying to understand if I have to shut down the O2 for some reason (for example maybe it shorted out due to condensation and reads full lean) what are the above toggles doing and what might my options be to get home under my own power until I can replace the O2.
    Read the fourth "Wideband O2 Sensor Note" near center of this webpage:
    http://forums.holley.com/showthread....ension-Harness (Wideband O2 Sensor Info)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

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    1. Thanks, as this solidifies my understanding.
    2. One follow-up (still trying to wrap my mind around this one): I understand what you're saying that correction is still happening to maintain the Target A/F Ratio Table, but slower. Do the corrections required to maintain the target get stored somewhere or are they just immediately applied to the base value at that point in the map at that particular time since the Learn Table won't modify the Base Fuel Table?

    Regarding O2 replacement/limp home - for the 4th sensor note, the comment "at least at idle", does this mean I could not run near normally (I say near normally because I know there would be no feedback to make minor corrections if needed) at higher rpm/load conditions until I replace the O2? Is there ever a scenario where you think I could run without the O2 for extended periods or is it always required to some degree? I'm just thinking carburetor - once it's jetted properly, one usually doesn't go back in and mess with it. Can the same hold true for EFI - once it's mapped properly (learned), can the loop back be shut off and still provide a decent running motor? Just curious on this last question.....

    Thanks for the help!

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
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    Quote Originally Posted by rvander68 View Post
    Do the corrections required to maintain the target get stored somewhere or are they just immediately applied to the base value at that point in the map at that particular time since the Learn Table won't modify the Base Fuel Table?
    No, they don't get "stored" anywhere without the Learn Table enabled. And that's the point...the Closed Loop is left functioning off the Base Fuel Table (whether it's good or bad) and corrected by the WBO2 sensor feedback. If the Base Fuel Table wasn't well tuned (before disabling the Learn Table), the Closed Loop Compensation has to correct more than it would normally (hence slightly longer work).

    This scenario really shows it's inefficiency when the engine quickly accelerates past those Fuel Table lb/hr cells, because the Closed Loop Compensation doesn't have the time to correct the AFR to the programmed Target A/F Ratio Table. Although it will at steady state cruising speeds. This is why a well tuned Fuel Table is so important; so the engine runs strong & efficient under all circumstances.

    Regarding O2 replacement/limp home - for the 4th sensor note, the comment "at least at idle", does this mean I could not run near normally (I say near normally because I know there would be no feedback to make minor corrections if needed) at higher rpm/load conditions until I replace the O2?
    Again, if the entire Fuel Table is well tuned, you should be able to run in Open Loop for an indefinite period of time (even at WOT). However, without the WBO2 sensor providing corrective feedback, the EFI is almost as inefficient as a carburetor because now it can't fine-tune (correct) for weather conditions, travel conditions, improved driveability, etc. Of course, just be sure to clear the Learn Table if it's been corrupted by a failed WBO2 sensor.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #5

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    Awesome. This clears it up perfectly for me. Many Thanks!

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