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Thread: 7747 Won't Enter Closed Loop At Idle

  1. #1
    Electronic Ignition!
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    7747 Won't Enter Closed Loop At Idle

    I have read hundreds of posts on this forum and it has been really helpful, but I think I have a new problem...

    Vehicle: '85 Toyota FJ60, 4-speed manual
    Engine: 89 C1500 5.7L TBI, all stock except that AIR system has been removed
    ECM: 7747 from the 89 C1500
    BCC: ASDW, no modifications

    Problem: Failed smog due to high CO at idle (0% CO at 2500rpm). I think my problem is that the ECM is not staying in Closed Loop at idle

    What I have done:
    1. Verified sensors and actuators (MAP, TPS, IAC, EGR, CTS & ground) are nominal
    2. When I raise idle (either with pedal or adjustment screw) to >850rpm the ECM will enter closed loop. When I reduce rpm it drops back into open loop. Target idle in the bin is 600-650 depending on CTS. I think the reason it enters CL at higher rpm is due to the "RPM above which open loop idle is forced off" (825rpm).
    3. Verified O2 sensor (singe wire installed in OEM manifold) is moving between 0.2-0.8mV in closed loop
    4. Confirmed Park/Neutral switch input (B10 to ECM) is OPEN = Drive
    5. Checked for vacuum leaks (not 100% sure there isn't a leak somewhere). MAP is seeing 20-24" at idle
    6. Rebuilt throttle body
    7. Verified fuel pressure (14psig)
    8. Tried biasing the TPS to 1.5V at idle to try to force closed loop (juicing the "Maximum TPS for Open Loop Idle" parameter") (didn't work, does this ECM set 0% throttle at key on? I saw conflicting info)
    9. Lots of other stuff that didn't make a difference
    I read in one posting that "older TBI trucks didn't really enter CL at idle" but it's hard to figure out what that really means.
    I am at the point where part of me wants to just drive the idle speed to 900rpm to force closed loop and try to pass smog, but... the engineer in me needs to figure out wtf is going on.
    Thanks for any help, again this forum has been a huge help to me!
    Adam
    Last edited by SBAdam; 2 Weeks Ago at 05:04 AM. Reason: messed up the post title somehow

  2. #2
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    has o2 been replaced? i've replaced 1 wire with 3 wire o2s. 3 wire is heated and will get onto closed loop sooner. i also only use ac delco here. i assume you have a cat for emission purposes.

  3. #3
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    Thanks for the reply. I did replace the O2 sensor. I think the new sensor is Bosch (which I now know is not the preferred brand. I think the sensor is working, though, since I can force closed loop by increasing the rpm. Granted, that is my interpretation of what is happening and I am not an expert.
    I am open to using a heated sensor, but have read that the single wire in the oem manifold position (like I have) should be good.
    Yes, I have a brand new CARB certified catalytic converter that seems to work great when the vehicle is running in closed loop (passed the 2500rpm emissions test with flying colors).
    Last edited by SBAdam; 2 Weeks Ago at 07:42 AM.

  4. #4
    Super Moderator dave w's Avatar
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    Attached is the ASDW chip file.

    Screen shot below shows there are several Open Loop and Closed Loop parameters.

    Considerable trial and error tuning required to get closed loop working to pass emission testing.

    dave w

    7747 Open_Closed loop.jpg
    Attached Files Attached Files

  5. #5
    Fuel Injected!
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    Have a look at the ASDZ idle closed loop settings. There are many GM files that go open loop at idle and none with any mileage have a prayer of passing emissions until that is fixed. I fix this quite often here in California, Dave W has you on the correct path, keep in mind all variables have to be "set" for closed loop to enable and stay enabled. Always convert to a heated sensor. As for the junk ass AC-Delco o2 sensors, I have thrown plenty away and always use Bosch or NTK, so, each to his own.
    -Carl

  6. #6
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    Quote Originally Posted by In-Tech View Post
    As for the junk ass AC-Delco o2 sensors, I have thrown plenty away and always use Bosch or NTK, so, each to his own.
    i found the complete opposite. i do use NTK and bosch where the OEM uses them though (jeep and subaru)

  7. #7
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    Thanks. I am leaning toward manually setting the idle above 900rpm for the emissions test. I have confirmed that this forces CL idle due to the "RPM above which open loop idle is forced off" = 825.
    Another option would be to fake the VSS to show >4mph at idle... From an emissions/engine operation perspective that would be better (ECM will manage idle to 650). Not sure how faking the ECM into thinking the vehicle is moving would affect anything (this is a manual transmission). Anyone have thoughts on this?
    I am trying to avoid tuning (kinda strange to say in this forum, I know) since I am seeing the referee and don't want the risk of him flagging the cal file somehow, but that might be the better solution.
    Thanks again
    -Adam

  8. #8
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    If you are located in California they won't let you raise the idle speed :(
    -Carl

  9. #9
    Super Moderator Six_Shooter's Avatar
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    When's the last time you did a tune up?

    There's really no reason that a stock engine (assuming, since there's no indication otherwise), shouldn't pass emissions with a stock bin, though the lack of AIR system might be the culprit here and I'm surprised you haven't failed on that alone.
    The man who says something is impossible, is usually interrupted by the man doing it.

  10. #10
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    Quote Originally Posted by Six_Shooter View Post
    When's the last time you did a tune up?

    There's really no reason that a stock engine (assuming, since there's no indication otherwise), shouldn't pass emissions with a stock bin, though the lack of AIR system might be the culprit here and I'm surprised you haven't failed on that alone.
    Plenty of tired engines don't pass smog in open loop. I have fixed quite a few of these over the years just getting them back in closed loop alone. Fixing the tune on tired engines helps even more.
    -Carl

  11. #11
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    AIR system should only be required on on old cats. my old caprice had the cat replaced and air system was hooked up. when I removed it the air pipe to the cat was present and hooked up but blocked inside from manufacturer

  12. #12
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    Quote Originally Posted by Six_Shooter View Post
    When's the last time you did a tune up?

    There's really no reason that a stock engine (assuming, since there's no indication otherwise), shouldn't pass emissions with a stock bin, though the lack of AIR system might be the culprit here and I'm surprised you haven't failed on that alone.
    The AIR system was removed due to failed pump and the emissions system is being certified compliant to 1991 model which eliminated the AIR system. Interestingly, the AIR solenoid valve was defective and likely never actually operated.
    With respect to tune up, it is a good point, but since the vehicle passed the 2500rpm test I have assumed (perhaps incorrectly) that the engine is operating nominally. I am replacing the plugs with the recommended AC Delco parts, but not planning on replacing distributor parts. Timing is set at 0deg when EST is disconnected.

    Anyone have feedback on my idea to force closed loop idle by feeding a VSS signal above 4mph? Not convinced that is a good solution... I would only use this in the short term (I am convinced the right long term solution is to tune the calibration file per In-Tech’s experience).
    thanks!
    -Adam

  13. #13
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    Problem: Failed smog due to high CO at idle (0% CO at 2500rpm). I think my problem is that the ECM is not staying in Closed Loop at idle
    In order to get right exhaust mix you need right mix of fuel and air and good combustion. Combustion is helped by heat in combustion chamber. Tailpipe emissions are also aided by hot exhaust manifolds. The heat encourages unreacted HC, CO, O2 to party together.

    Do you have report with HC / CO / CO2 / O2? This report can be helpful.

    At 2500 RPM factors like leaking valves or rings and even worn cams have a lower effect. Passing emissions at 2500 rpm does not indicate the plugs and wires are at their best.

    First advice might be to look at a '91 calibration if engine is being certified as a '91. Later calibrations are less likely to be open loop at idle.
    Make sure you have plenty of heat in engine. New T-stat? ThermAC / hot air tube connected? 94 deg F minimum intake air and 195 deg F minimum coolant temp is basis for stock emissions readings.
    It won't hurt to bump timing by a degree or two on a high mileage engine.
    Fuel quality OK? Introducing alcohol is a cheat but it can displace HC with O2 which can lower tailpipe readings.
    Plugs, wires, tune-up should already have been done.
    Fresh oil can help. Old oil accumulates HC waste which can be introduced into intake through PCV system.
    I would not play with VSS signal. Better to have a calibration with the correct values in it.

  14. #14
    Super Moderator dave w's Avatar
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    I'm wondering if the idle minimum air needs adjustment? This website has good general information: https://www.gmcmi.com/wp-content/upl...alibration.pdf

    I'm wondering if the injectors are in need of service? https://www.gbreman.com/


    dave w

  15. #15
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    [QUOTE=1project2many;86776]

    Do you have report with HC / CO / CO2 / O2? This report can be helpful.

    4E949A42-09A4-487B-BC2B-8A94B70EDA1D.jpg

    “First advice might be to look at a '91 calibration if engine is being certified as a '91. Later calibrations are less likely to be open loop at idle.”

    Yes, that is just what I was thinking. Will look this evening.

    “Make sure you have plenty of heat in engine. New T-stat? ThermAC / hot air tube connected? 94 deg F minimum intake air and 195 deg F minimum coolant temp is basis for stock emissions readings.”

    Tstat is 205. Fans come on at 192/195, basically as soon as tstat opens. Might need to tune this let the engine get hotter.
    Will pick up a new cap and wires to go with the new plugs.
    Fuel is good. ThermAC is in place. Oil is new.

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