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Thread: EGR tuning $8D S_AUJP

  1. #1
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    EGR tuning $8D S_AUJP

    Over my last weekend I was able to finally fix the EGR tube on the fiero. Last night I spent some time patching DC values and qualifiers from $24(fiero bin) and other $8D bins. The EGR DC table was propagated using values from $24, along with TPS threshold values. I cant open TP at work but iirc, $24 uses engine load in kpa for its qualifiers to enable EGR DC, also uses a qualifier for MAX threshold(higher loads). $8D uses TPS. On my way into work this morning the EGR looked like it was functioning normally, which is good. I did spot a possible issue, though. Let me start with the 3D EGR DC table, $24 uses a higher resolution table, but doesnt command and EGR DC above 50kpa, and max DC is ~44%. $8D commands 100% DC(which I didnt use those values) upto 80-90kpa, which I didnt use either just zeroed the table above 50kpa. Now in theory there wouldnt be any EGR DC commanded above 50kpa(in my mind) but I noticed EGR DC was 44%(at times) in the 60-90kpa areas. Thats weird to me because the table is zeroed out in those cells? If I dont want any EGR DC above 50kpa, theres nothing in the XDF to disable that. Or am I not understanding that right? There is only the TPS qualifiers, oh and the coolant temp V. EGR DC multiplier table. Im also going to assume that since the EGR DC table only reaches to 2000rpm that the values are interpolated above that? I didnt see a max rpm for EGR DC in the XDF either, possibly not found in hac? Or does it continue to operate no matter what RPM?


    I will try to remind myself to get a datalog on the way home today.

    Thanks!
    '86 Grand National

  2. #2
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    Quote Originally Posted by 34blazer View Post
    Over my last weekend I was able to finally fix the EGR tube on the fiero. Last night I spent some time patching DC values and qualifiers from $24(fiero bin) and other $8D bins. The EGR DC table was propagated using values from $24, along with TPS threshold values. I cant open TP at work but iirc, $24 uses engine load in kpa for its qualifiers to enable EGR DC, also uses a qualifier for MAX threshold(higher loads). $8D uses TPS. On my way into work this morning the EGR looked like it was functioning normally, which is good. I did spot a possible issue, though. Let me start with the 3D EGR DC table, $24 uses a higher resolution table, but doesnt command and EGR DC above 50kpa, and max DC is ~44%. $8D commands 100% DC(which I didnt use those values) upto 80-90kpa, which I didnt use either just zeroed the table above 50kpa. Now in theory there wouldnt be any EGR DC commanded above 50kpa(in my mind) but I noticed EGR DC was 44%(at times) in the 60-90kpa areas. Thats weird to me because the table is zeroed out in those cells? If I dont want any EGR DC above 50kpa, theres nothing in the XDF to disable that. Or am I not understanding that right? There is only the TPS qualifiers, oh and the coolant temp V. EGR DC multiplier table. Im also going to assume that since the EGR DC table only reaches to 2000rpm that the values are interpolated above that? I didnt see a max rpm for EGR DC in the XDF either, possibly not found in hac? Or does it continue to operate no matter what RPM?


    I will try to remind myself to get a datalog on the way home today.

    Thanks!
    Almost all values in GM ECM tables are interpolated. If you go from say 100% @ 2,000 down to 0% @ 2,4oo and are sitting at say 2,200 exactly, you will be sitting at 50%.

  3. #3
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    The table only goes to 2000 rpm. My question for that part was, what is the rpm limit for the EGR DC? Its not listed in the XDF.
    '86 Grand National

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    Scratch that. EGR is functioning properly and my questions have been answered. This morning I observed effects of the EGR and found that it provides no increase in fuel milage. Depending on the duty cycle, the impact negatively affected fuel milage. As soon as DC rose above 30% I noticed an increase in BLM counts. Not satisfied with that observation I toggled EGR on and off while highway mode was active, watching NBO2 readings similtaneously. With EGR DC at or above 30%, the A/F mixture would lean out, ~30-50mV. While it helps with emissions, it doesnt help fuel milage at all, at least in my case. Toggled off, the BLM counts fell back down to where im used to observing them, some cells fell by 6 counts. So I have no use for EGR anymore.
    '86 Grand National

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    not sure how 8D accounts for it, but you did have spark being added due to EGR active, yes?

    i've had good results with EGR enabled on 60V6 applications, after some tweaking of the fueling and spark modifiers for when EGR is active anyways.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  6. #6
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    BLM is only giving you the difference between the airflow the ECM thinks is there (after subtracting out the EGR that it thinks is there) compared with what is actually happening on the engine, not the actual fuel economy. I think that generation of ECM had a BPC vs. EGR calibration in there somewhere and any error in that calibration would show up as a BLM shift. There will be an emissions benefit but you should see a slight mileage improvement when looking at the pulse width at the same vehicle speed - you'd need to log injector pulse width, RPM, vehicle speed and integrate pulse width * RPM and compare against miles (or kilometres) driven to get at least a semi-accurate reading. Also EGR is usually set up to allow more advanced ignition timing - maybe 5 to 8 crank degrees - which should help your efficiency numbers. I don't know if I've ever seen a calibrated EGR system make efficiency drop, but certainly if the timing isn't adjusted up that can happen. That being said, with EGR there is a peak efficiency point where you've lowered NOx as much as you can and advanced the timing as much as you can and if you increase the flow rate any more then you get an efficiency drop - if some is good, more is not necessarily better. Just like tequila. It also should help lower the exhaust temperatures at part-throttle.
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  7. #7
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    I know $42 has a scaler for EGR on/off, iirc $88 uses a modifier table, and $24 as well. There isnt any modifier I could find for spark or fuel in the S_AUJP xdf, and im not capable of finding something like that in the disassembly yet. I will make a note of the items to be logged and will record while on my way home from work. Even $24 has more modifiers that could be used. When I get home ill also look thru other $8D masks to see if there is more available items, if so ill put them in the S_AUJP xdf as long as the locations match up.
    '86 Grand National

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    Quote Originally Posted by RobertISaar View Post
    not sure how 8D accounts for it, but you did have spark being added due to EGR active, yes?

    i've had good results with EGR enabled on 60V6 applications, after some tweaking of the fueling and spark modifiers for when EGR is active anyways.
    can you share your EGR DC table, unless it is untouched from the factory? the 2.8 in the fiero is bone stock, well, with the exception of the ported headers.
    '86 Grand National

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    wouldn't be of much use to you, i use the 3 tower digital setups, not the EVRV used before them. also comparing iron head 2.8 to aluminum head 3.1 and 3100 is another lopsided comparison.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


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    Quote Originally Posted by daleulan View Post
    That being said, with EGR there is a peak efficiency point where you've lowered NOx as much as you can and advanced the timing as much as you can and if you increase the flow rate any more then you get an efficiency drop - if some is good, more is not necessarily better. Just like tequila. It also should help lower the exhaust temperatures at part-throttle.
    IIRC, that threshold is where the amount of exhaust gasses in the chamber make up so much of the air/fuel charge where misfires are inevitable. i would take a guess at saying that a stronger ignition system would allow higher concentrations.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  11. #11
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    Quote Originally Posted by RobertISaar View Post
    IIRC, that threshold is where the amount of exhaust gasses in the chamber make up so much of the air/fuel charge where misfires are inevitable. i would take a guess at saying that a stronger ignition system would allow higher concentrations.
    well, I just set the DC at 60 in the 50-60 kpa MAP range, and 30-40% in the 40 kpa range, havent noticed a misfire yet. $8D has the DC set at 100% thru most of the range, I dont think the little 660 could handle that LOL.
    '86 Grand National

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    I managed to find a PDF copy of the ANHT hac(limited access at work), looks like $8D uses EGR partial pressure to adjust fuel requirments, the equation is there so Ill have to figure out which way to adjust that table so it doesnt skew my BLM counts too much. Not sure on the the spark yet....
    '86 Grand National

  13. #13
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    so using this calc....

    VE CALC = ((MAP - EGR part press) * CYL VOL)/((MAT + 233) * 128))

    increasing EGR part press value will reduce VE? trying to get the BLM's to not jump up 5-6 counts while EGR is active, already had some bogging this morning when the engine wast totally up to running temp.
    '86 Grand National

  14. #14
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    The PDF of the ANHT is seriously flawed and has errors even though it helped to get the AUJP commented.
    Download the AUJP files from Moates site (or here if EagleMark has them)
    AUJP_JP2.zip is updated and commented as much as was known at the time it was posted.
    ALL calibration values are in the S_AUJP there is nothing to add. All addresses in the calibration section of the bin are accounted for.
    Verification of some of the uncommon items is still needed.
    Nobody has all the info on them and I was hoping more people would investigate them and help solve them all.
    If you find anything that could or should be clarified, post it up or something so it can be corrected.
    Thanks,
    John
    86 Monte, 406, Hyd Roller, 700R4 beefed, G3-APU1 and NVSRAM 730, S_AUJP

  15. #15
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    John, Moates no longer has fileman, Craig gave us all the files for safe keeping when their site crashed and decided to leave it that way.There is a link on Moates site to here.

    http://www.gearhead-efi.com/gearhead-efi/

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