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Open loop

Discussion in '1st Gen. Tacomas (1995-2004)' started by 01Montaco, Jan 17, 2019.

  1. Jan 17, 2019 at 11:56 PM
    #1
    01Montaco

    01Montaco [OP] Well-Known Member

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    While driving to work tonight I noticed that my ultra guage was showing an open loop status while on the interstate.

    It would show closed loop when I let off the throttle all the way but would return to open loop when I would give it more than about a 1/4 throttle.

    I wasn't seeing it go back to open loop while accelerating in 1st through 4th no matter how much throttle I gave it once off the interstate.

    My only thoughts would be something to do with the O2/ fuel-air sensors or the MAF.

    The motor was up to full operating temp when I noticed this
    -01 5vz standard
     
  2. Jan 18, 2019 at 7:11 AM
    #2
    Glamisman

    Glamisman Well-Known Member

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    I am thinking engine coolant temperature sensor / stuck open thermostat. Any way to chart the coolant temp?
     
  3. Jan 18, 2019 at 7:13 AM
    #3
    Dalandser

    Dalandser ¡Me Gustan Las Tacos-mas!

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    Empty Wallet Mod
  4. Jan 18, 2019 at 9:55 AM
    #4
    01Montaco

    01Montaco [OP] Well-Known Member

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    Replaced coolant and T-stat last year because the old one was stuck open.

    Temp raises linearly up to 188 consistently ever since. At highway speeds it sticks around 190-195. The highest it has got on me is 201 pulling a long hill in the summer.


    Once the engine load drops after leveling out the temps return to 190-195.

    One other thing I've noticed is that the intake air temp will default to reading 55-65 even if the ambiant temp is in the single digits.

    On my way home it was reading 23 iac while it was 21 degrees out. Throttled up onto the interstate and the computer went into open loop. The iac went up to 59 and stayed there the rest of the trip
     
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  5. Jan 18, 2019 at 12:03 PM
    #5
    Dalandser

    Dalandser ¡Me Gustan Las Tacos-mas!

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    Not trying to hijack your thread - just sharing that I've been encountering a similar situation on my project truck - no CEL, headers only so no O2 / exhaust sensors, 170* thermostat because of supercharger, champion 3 row radiator with a rising idle from 1500 at cold start up to 2400 after a few minutes and getting "Open Loop: Insufficient Engine Temperature" while Scangauge & Bluetooth OBD show live data of coolant temp from ambient to 184*. I read on another thread that "operating temp" begins at 167* for the ECU to throw the truck into closed loop, but I can't confirm that. Curious why the temp could be being sensed with perceived accuracy, yet the ECU is saying insufficient temperature, staying in open loop, and having the idle climbing (I have not confirmed that this is a symptom of the open loop situation, but it seems like it could likely be related).
     
  6. Jan 19, 2019 at 1:00 PM
    #6
    zero4

    zero4 Metal Cutter

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    I don't think the 167° is true. My truck will be in closed loop much colder than that. My truck runs closed loop most of the time. The only time I notice open loop is if I'm cruising on the fwy & let off the throttle, like with the RPM around 2K or above, and always when I exit an off ramp & left off the throttle. I can tell when it goes to open loop as the exhaust note changes. Rarely do I ever see open loop crusing around on the street unless I'm speeding. I also get open loop climbing a grade.


    Here's my truck this morning when I left the house, not up to temp yet (loop indicator at the top RH corner for the UG).
    20190119_110757.jpg


    Open loop off the throttle exiting the fwy.
    20190119_122415.jpg


    Open loop going up a hill on the fwy.
    20190119_131348.jpg


    As for the OP, that's weird, I've never noticed my truck behave like that, even with my a/f sensor on it's way out. Just had to replace it a week ago do to the heater circuit failing. I've never had to replace the rear O2, only the front. My original one lasted 9 yrs. The Denso replacement lasted 8 yrs. How old are yours?
     
    Last edited: Jan 19, 2019
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  7. Jan 19, 2019 at 2:43 PM
    #7
    01Montaco

    01Montaco [OP] Well-Known Member

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    That I don't know. They're at least 2 years old since I purchased the truck in 2017.

    I understand it going into open loop under full throttle in order for the motor to achieve the most power I just don't know why it won't switch back unless the throttle is let off all the way.

    Any thoughts on what might cause the MAF to revert to what I would assume is a default reading when this happens?

    I'll be replacing the intake within a few months because I don't like the K&N that the truck came with.
     
  8. Jan 19, 2019 at 2:50 PM
    #8
    zero4

    zero4 Metal Cutter

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    I can't remember the last time I full throttled my truck but yeah at full throttle or heavy load it should be in open loop, like when I climb a steep grade. Weird that it's not switching back. MAF & O2 sensors are the only thing I can really think of.

    My truck came with a full K&N FIPk system, hated that thing, I sold it & put a stock intake back on. Have you checked your MAF sensor to see if it's oily or gunked up? Try cleaning it with some electrical contact cleaner.
     
  9. Jan 19, 2019 at 4:40 PM
    #9
    01Montaco

    01Montaco [OP] Well-Known Member

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    Ya, that's my plan too. I did that about 3 months ago and haven't oiled the filter at all. Even if the PO over oiled it, it's been 2+ years since it's been oiled. Anything's possible though I guess
     
  10. Jan 19, 2019 at 4:51 PM
    #10
    zero4

    zero4 Metal Cutter

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    Ah well I don't think it's the MAF then, well not being dirty anyway, only if it might be defective. 3 months is not long at all even if it were oily from an over oiled filter. But cleaning it again won't hurt & is worth a try as you said.
     
  11. Jan 19, 2019 at 9:15 PM
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    Glamisman

    Glamisman Well-Known Member

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    I did some digging and I think that it is operating as designed...

    http://obdcon.sourceforge.net/2010/06/obd-ii-pids/

    Mode 1 PID 3

    A0 open loop due to insufficient engine temp
    A1 Closed loop using O2 sensor feedback to determine fuel mixture
    A2 open loop due to engine load or fuel cut due to deceleration
    A3 open loop due to system failure
    A4 closed loop using using at least one o2 sensor but there is a fault in the feedback system.

    hope this helps.
     
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  12. Jan 20, 2019 at 10:27 AM
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    DrZ

    DrZ Well-Known Member

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    Could it be a misadjusted throttle position sensor? The computer thinks the throttle is open more than it actually is?
     
  13. Jan 21, 2019 at 8:08 PM
    #13
    1997tacomav6

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    My truck is similar to yours,
    My open loop changes at 154 degrees to close loop.
    My ECU goes into open look when ever I take my foot off the pedal and when I’m on full throttle.
    Otherwise dam ECU keeps the truck in closed loop

    Screenshot_20190121-205755_Gallery.jpg
     

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