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Thread: 7747 Won't Enter Closed Loop At Idle

  1. #16
    Fuel Injected! PlayingWithTBI's Avatar
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    Just a silly question - what Cat do you have and how old is it?

  2. #17
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    Cat is brand new CARB certified.

  3. #18
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    Quote Originally Posted by 1project2many View Post
    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
    It looks like ARJX is the right bin: 1991 manual for *California Emissions* vehicles. I compared to my current ASDW and there are a number of differences, though I didn’t see anything obvious that would solve my problem (don’t really know what the root of the problem is). I might switch to this calibration just to see if having a better match for the engine (no AIR), a later model year, and a California specific file will allow/enable closed loop idle.
    I welcome other suggestions and questions.
    thanks everyone for the guidance
    -Adam

  4. #19
    Super Moderator dave w's Avatar
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    ARJX information attached.

    dave w
    Attached Images Attached Images
    Attached Files Attached Files

  5. #20
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    Thanks for posting that.

    I believe higher HC and O2 readings show incomplete combustion more than incorrect AFR. Forcing closed loop with higher O2 ratio will cause ecm to respond with more fuel. I'm thinking that will only make high HC reading higher.

    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.
    Record average O2 reading now (should show slightly lean) and again with higher temps. Can always unplug a fan for a short time and monitor O2 reading as engine temp climbs. I'm thinking around 215 or so you'll see lower average O2 reading. This indicates better combustion.

    It looks like ARJX is the right bin: 1991 manual for *California Emissions* vehicles. I compared to my current ASDW and there are a number of differences, though I didn’t see anything obvious that would solve my problem (don’t really know what the root of the problem is). I might switch to this calibration just to see if having a better match for the engine (no AIR), a later model year, and a California specific file will allow/enable closed loop idle.
    I welcome other suggestions and questions.
    thanks everyone for the guidance
    There is considerably more spark advance at idle in ARJX. This alone may be enough to see an O2 sensor signal difference and to pass idle emissions. I have copied the first five rows of the main spark tables from both calibrations for comparison:

    Code:
    ASDW:
    16.17	16.17	16.17	16.17	16.17	14.06	12.3	9.14	6.33	4.22	2.11	0	-1.76	-2.81	-3.87
    16.17	16.17	16.17	16.17	16.17	16.17	16.17	9.14	6.33	4.22	2.11	0	0	0	0
    16.17	17.23	17.23	17.23	16.17	14.06	12.3	9.14	7.03	4.22	2.11	1.05	0	0	0
    15.12	16.17	18.28	18.28	16.17	14.06	12.3	9.14	7.03	4.22	2.11	2.11	2.11	-0.7	-0.7
    14.06	17.23	18.98	18.28	16.17	14.06	12.3	10.2	9.14	7.03	5.27	5.27	4.22	2.11	2.11
    
    
    ARJX:
    20.04	20.04	20.04	20.04	17.23	14.06	12.3	9.14	6.33	4.22	2.11	0	-1.76	-2.81	-3.87
    20.04	20.04	20.04	20.04	20.04	18.28	16.17	9.14	6.33	4.22	2.11	0	0	0	0
    20.04	20.04	20.04	20.04	17.23	14.06	12.3	9.14	7.03	4.22	2.11	1.05	0	0	0
    15.12	16.17	18.28	18.28	16.17	14.06	12.3	9.14	7.03	4.22	2.11	2.11	2.11	-0.7	-0.7
    14.06	17.23	18.98	18.28	16.17	14.06	12.3	10.2	9.14	7.03	5.27	5.27	4.22	2.11	2.11

    HTH

  6. #21
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    Thanks! That is really helpful. I will post O2 sensor data for current operation and with higher CTS temp.
    Definitely going to change to ARJX.

  7. #22
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    As an experiment, the base timing could be advanced 4 degrees BTDC instead of ZERO degrees BTDC to see what happens to emissions.

    dave w

  8. #23
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    Quote Originally Posted by dave w View Post
    As an experiment, the base timing could be advanced 4 degrees BTDC instead of ZERO degrees BTDC to see what happens to emissions.

    dave w
    True - though I can't get that feedback without a smog test, right? I think we are on the right track, I am going to examine the main spark tables more closely. The fact that they are significantly different is telling.

  9. #24
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    Your thermostat and fan temps seem backwards to me. Original T-stat should be a 195* and fan on off temps should be 200-215ish or higher.

    I agree with Dave's suggestion on getting the injectors cleaned, Mr Injector does really good work cheap. Noticeable difference when I had mine done.

    I also agree the California .bin you found is good place to start. Might even be able to find an original GM prom chip. Or Dave can flash that CAL .bin onto an original prom for you.
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  10. #25
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    It's been a few years but doesn't your NOx go up with too far advanced timing? I didn't see what you NOx was on the slip.

  11. #26
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    Quote Originally Posted by SBAdam View Post
    True - though I can't get that feedback without a smog test, right? I think we are on the right track, I am going to examine the main spark tables more closely. The fact that they are significantly different is telling.
    You can't get detailed feedback, no. But you can look at the average O2 voltage to see if the amount of free oxygen (O2) in the exhaust is decreasing. With decreasing oxugen, the O2 signal voltage should increase slightly.

    Your thermostat and fan temps seem backwards to me.
    Agreed. With the reported temps the fan is likely to be on all the time.

    It's been a few years but doesn't your NOx go up with too far advanced timing? I didn't see what you NOx was on the slip.
    Indirectly, yes. NOx increases with higher temperature combustion. Advancing timing too far causes combustion temp to increase. But the numbers suggest that combustion temp is not yet hot enough...

  12. #27
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    Ok, with the fan temp sensor unplugged I let the CTS get to 215-220 for a few minutes. O2 mV average is around 750. At 189F the average is about the same, maybe slightly higher. It wasn’t a tightly controlled test (should have run for 20 minutes or so!instead of ~5), I think the point is still valid that the engine should be running with hotter combustion. I will look for a temp switch closer to 205/210
    I am questioning the recommendation for a lower temp tstat, though. I thought this would bring the radiator into the loop at a lower temp and, at least on the highway or when fans are running, keep the engine temp lower.
    Last edited by SBAdam; 02-27-2021 at 12:00 AM. Reason: Typo

  13. #28
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    Lower temp T-Stat? The comment about fan and thermostat temp being backward? I wouldn't change the thermostat.

  14. #29
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    I mentioned the thermostat being odd. Adam says his was 205* I think an original 195* is plenty, especially if the fan on/off temps are fixed.

    Use the fans to regulate the temp.
    89 K1500 Scottsdale 5.7L 5spd 3:42 RamJet cam Dart iron TBI heads 427 PCM swap
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  15. #30
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    Hey if the OEM configuration had a 195 tstat I will do that. I read conflicting info on other sites and what is in the engine now came with the donor vehicle (which was hacked together and not reliably the factory set up in any way).
    I think the fan temp switch is actually ok, though, since it is in the return line to the engine. Low is 199F and high is 210F. I will change the tstat and see if engine temp runs hotter with fans controlled by the switch. That’s probably easier than trying to think through it. Can always disconnect the 199 switch too.

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