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Thread: Greenhorn

  1. #11
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    Who's car 'rarely' enters PE? I thought that was one of the main reasons for changing the factory tune; to get the open loop tables cleaned up to make even power.

    I don't see KR unless I am hard on the throttle and not in PE (stock tune). I also would not put much faith in the 'commanded AFR'. There are things going on that do not show up in the commanded value, but show up with a wideband O2.

  2. #12
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    My car rarely enters PE mode...only gets there when I floor the accelerator. I don't drive like that unless I am on a two lane and need to pass. Commanded AFR tells exactly which mode your are operating in. The computer knows if you are in PE mode or not and figures out if you need 14.6AFR or the value off the AFR in PE mode table{B0901}. Maybe that isn't the actual AFR, but that doesn't matter. What matters is what table is being used under the conditions you have recorded. A wideband won't tell you when you have entered PE mode as precisely as the PCM that puts it into this mode. The commanded AFR tells you what table you should change when changing the timing based on knock retard. The wideband is of little use for timing changes. Fueling changes are a different story. Operating in PE mode means using a lot of fuel. If the computer is using an AFR of 14.6 for the non-PE mode and 12.5 for PE mode, operating in PE mode all the time is consuming almost 17% more fuel for a given RPM and MAP. That's a waste of fuel.

  3. #13
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    I never said to run the car in PE mode all the time. I stated that I do not see KR unless the engine is under heavy load and not in PE.

    Your car goes into PE mode alot more often than you think. An ICE cannot run at stoich under heavy loading without generating tremendous amounts of heat that will melt pistons. Engine load and time control the addition of fuel for cooling means.

    How does the commanded AFR tell you which table you should change when changing timing to reduce KR? The timing tables are not related to the AFR. The timing tables are based on RPM & engine load.

    What are your main objectives by modifying the PCM parameters?

  4. #14
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    AFR is a function of the mode you are in: PE or non-PE.
    PE mode uses the table I referenced in my last message and commands the AFR to whatever is dictated by said table (around 12.5).
    Non-PE mode tries to run 14.6

    When the commanded AFR is 14.6, PCM is in non-PE mode
    When the commanded AFR is near 12.5, PCM is in PE mode

    Now you can use the map feature to figure out where you need to pull timing. If you create a map of KR based on rpm and map, create another map of commanded AFR based on rpm and map. This second map will show the AFR for the given cells. An average of 14.6 means that cell was in non-PE; if the average is 12.5 (or whatever the PE AFR is set to), then that cell is for PE mode; if your average is between 14.6 and 12.5, that cell is a mess and a combination of PE and non-PE. Don't adjust timing in that cell. For the cells that average 14.6, adjust the timing in the high octane spark table non-PE mode. For the cells that average 12.5, adjust timing in the high octane table PE mode. Make sure that your low octane tables aren't advanced past the their respective high octane table. The table names are misleading, they are the max an min timing used.

    I tune for mileage, but more power is a side effect. This method will reveal how often your vehicle is in PE mode...my vehicle only enters PE mode when I floor it. On my last logged trip, I only entered PE mode when I floored it and the PCM kept it there for 47 of the 50,000 data points I logged. That is less than .1% of the time. If I had not floored the throttle, I would never have entered PE mode.
    Last edited by ds8; November 22nd, 2006 at 04:53 AM.

  5. #15
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    So your method uses the commanded AFR as an indicator as to which timing table (PE or Non-PE/low Rpm or high Rpm) to change?

    Have you changed the PE enable parameters at all? My TB will enter PE mode when pulling up a long hill. It also enters PE every time the tranny kicks down.

    Are you seeing better mileage by reducing timing advance? If you tune for mileage, I am really surprised that you are not using a wideband and fine tuning the VE tables to get the stoich AFR dead on. I would think that the best mileage gains would come from fuel adjustments first and timing second.

    Have you documented any changes in the "engine torque" since you started changing the timing? Are you suspecting that GM negated increases in mileage and power in the programming in favor of lower emmissions?

  6. #16
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    The commanded AFR tells which table is being used in the mapped cells. This tells which table to change the advance in.

    I have changed the PE enable parameters. This is one way to get better mileage. I don't enter it when kicking down a gear nor do I enter PE on long hills.

    I'm not sure changing AFR can improve the mileage as much as timing can. I don't have the wideband so I can't be sure of that. I could probably do better with one. Here's my reasoning: the timing is so bad on that canned tune (it's 15 degrees too advance in my cruising zone) that the combustion process is fighting the piston travel. I would have to richen it up incredibly to get rid of that much knock. In that case, the wideband doesn't do me any good because I would be way down from 14.7 :1. Backing down the advance lets the engine run closer to 14.7 because there is no knock. Without knock, the combustion doesn't fight the piston travel resulting in better transfer of energy, and the AFR is lower so less fuel is used anyway. Once the timing is close, then a wideband could be used to tune VE and further change timing.

    I've found that the 3 TB's I've checked put out about 112 lb-ft of torque according to the pcm with the stock tune. With my tune I am putting out 116 1b-ft according to the pcm. I haven't checked in a while and have made some changes with 7.3.3, so I don't know where it is now.

    GM faces the issue of providing a single tune that works everywhere in the world. That is their handcuff, but I can tell you the stock tune is closer to optimum than the tune originally discussed here. By the way, that tune only put out mid 70's for max torque according to the pcm.

  7. #17
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    Now we are getting somewhere! I'm still not sure how the heavy-load engine heat is being removed without adding fuel, but we can discuss this in detail later. Obviously the PCM will add fuel to protect the engine and catalytic converter somehow.

    You have pulled 15 degrees of timing from the cells you cruise in and believe you are getting better gas mileage? What gain in mileage are you seeing? To keep everything in comparison, please state the vehicle specifics; ie 2wd 4wd 3.73 or 3.42 rear axle etc...

    You reason that the timing is advanced so far that the peak combustion pressure is achieved before the piston is even at TDC? 15 degrees is a major timing change. Most of the time I am seeing ~23-25 degrees of advance while cruising. Are you actually tuning to ~10 degrees of advance?

    You also reason that backing the timing off allows the engine to run closer to 14.7 because there is no knock. I am not sure how AFR is related to or controlled by knock. I have never seen the PCM change fueling based on KR. I do know that the O2 sensors and several parameters make the AFR sweep between slightly rich of stoich to slightly lean of stoich to make the catalytic converter do it's job when in closed-loop mode. Can you expand your thoughts on KR affecting fueling?

    How confident are you in the torque numbers and how the PCM is calculating them? Can you relate the numbers you have recorded to any reasonable torque values for our engine? Will you list the operating parameters that were in effect when the torque was 116 Ft# so we can discuss?

    I have chassis dyno data and several logged files of my vehicle that we should be able to use to compare and evaluate some of these results.

  8. #18
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    Now we are getting somewhere! I'm still not sure how the heavy-load engine heat is being removed without adding fuel, but we can discuss this in detail later. Obviously the PCM will add fuel to protect the engine and catalytic converter somehow.

    It does add fuel, that is the nature of the VE table. different loads and rpms have different VE's. therefore they will have a different fuel charge and most likely different AFR.

    You have pulled 15 degrees of timing from the cells you cruise in and believe you are getting better gas mileage? What gain in mileage are you seeing? To keep everything in comparison, please state the vehicle specifics; ie 2wd 4wd 3.73 or 3.42 rear axle etc...

    the canned tune was 2-3mpg worse than stock. I'm probably about 1-3 better than stock. 2wd 4.2 3.73.

    You reason that the timing is advanced so far that the peak combustion pressure is achieved before the piston is even at TDC? 15 degrees is a major timing change. Most of the time I am seeing ~23-25 degrees of advance while cruising. Are you actually tuning to ~10 degrees of advance?

    between 20 and 35 depending on load for the wait4me tune and 6 and 28 for my tune

    You also reason that backing the timing off allows the engine to run closer to 14.7 because there is no knock. I am not sure how AFR is related to or controlled by knock.

    knock can be eliminated by running rich...you see this on your own car when you said you have no knock in PE.

    I have never seen the PCM change fueling based on KR. I do know that the O2 sensors and several parameters make the AFR sweep between slightly rich of stoich to slightly lean of stoich to make the catalytic converter do it's job when in closed-loop mode. Can you expand your thoughts on KR affecting fueling?

    You would have to run extremely rich to eliminate the knock from 16 degrees too far advanced. It's easier and engine efficiency is better if you pull the 16 degrees than to run at 10:1 AFR.

    How confident are you in the torque numbers and how the PCM is calculating them?

    They are not close at all to what the engine really makes. They are used to make assements on what to do with the transmission. off topic - There is hardly any torque reduction when you use this number in the tables.

    Can you relate the numbers you have recorded to any reasonable torque values for our engine?

    assume 112 is proportional to 275 ft-lbs. then 116 gives you about 284lb-ft.

    Will you list the operating parameters that were in effect when the torque was 116 Ft# so we can discuss?

    too many to list

    I have chassis dyno data and several logged files of my vehicle that we should be able to use to compare and evaluate some of these results
    Last edited by ds8; November 22nd, 2006 at 07:34 AM.

  9. #19
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    F@&^%, You 2 are Wayyyy over my head.
    And I thank you! Now I have an idea of what things
    I need to learn.

    How bout a lil handholding for us newbies?

    I know I need a baseline before I can make any
    comparisons or adjustments.

    Please give me some direction on what is Really important to log and how.

    For instance:
    Use this set of PID's {........}
    Drive 10 miles city followed by 15miles Hwy and do 3 WOT from dig and 2 from ~45 - WOT and 2 from ~65 - WOT

    Then take note of the {...} and {...} .
    What you are looking for is fluctuations here and there.....blah blah

    I think if that kind of knowledge were passed along I would grasp it much easier than

    "Look at your VE table and keep X within 20% of Y @ 17* btdc"

    Would that be doable?

  10. #20
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    These are the ones I am using:

    OK DESCRIPTION CAPTION UNITS SYSTEM CH PARAMETER
    Y Calculated Injector Flow Rate (Generic scan mode only) INJFLOW Grams/s,Lbs/Min Fuel 2 GM.INJFLOW
    Y Calculated Load Value LOAD_PCT % Performance 1 SAE.LOAD_PCT
    Y Cam Phase Angle Desired CAMPA_DES Degrees Conditions 2 GM.CAMPA_DES
    Y Commanded Air Fuel Ratio B AFR_B :1 Fuel 1 GM.AFR_B
    Y Damped VSS DAMPVSS KMH,MPH Performance 0 CALC.DAMPVSS
    Y Delivered Engine Torque to Transmission TRQENG_B Nm,Ft-Lbs Transmission 2 GM.TRQENG_B
    Y Engine Coolant Temperature ECT °C,°F Temperature 1 SAE.ECT
    Y Engine RPM RPM RPM Conditions 2 SAE.RPM
    Y Ignition Timing Advance for #1 Cylinder SPARKADV Degrees Spark 1 SAE.SPARKADV
    Y Injector Pulse Width Injector 1 INJ1PW ms Fuel 2 GM.INJ1PW
    Y Intake Air Temperature IAT °C,°F Temperature 1 SAE.IAT
    Y Intake Manifold Absolute Pressure MAP kPa,inHg Air 1 SAE.MAP
    Y Last Shift Time SHIFTLAST Seconds Transmission 1 GM.SHIFTLAST
    Y Long Term Fuel Trim - Bank 1 LONGFT1 % Fuel 1 SAE.LONGFT1
    Y Retard Due to Knock KR Degrees Spark 1 GM.KR
    Y Short Term Fuel Trim - Bank 1 SHRTFT1 % Fuel 1 SAE.SHRTFT1
    Y Throttle Position TP % Throttle 1 GM.TP
    Y Transmission Fluid Temperature TFT °C,°F Temperature 1 GM.TFT
    Y Vehicle Speed Sensor VSS KMH,MPH Conditions 1 SAE.VSS

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