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Thread: What is causing this?

  1. #1
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    What is causing this?

    I'm trying figure out why timing advance is being pulled at a steady state, low RPM, steady throttle. It's inducing a down right irritating surge. It happens in between 1400 and 1800 rpm and .22 g/cy. About 15 - 18 deg is being pulled. It's like something is confusing the ecm. It's instantaneous. I have both hi and lo tables matched. It appears that the ecm is referencing the coast down table for a split second, or possibly adaptive idle???? I'm at a loss what to do at this point. I will gladly pay someone to help if needed, and I promise to keep your secret trick to myself, if that's important to you....

    To save you time, you can see an example of this oddity at frames 26,452, 24,850, or 24,936.

    The log was after I flashed all new timing tables I shamelessly stole from an LS7 tune that RWTD posted after I totally screwed up my tables. I have addressed the knock retard areas that are in the knock retard histogram. If you see anything else in the tune or log that would demonstrate idiocy, please feel free to inform me...LOL

    The tune file is what was loaded during this log.
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  2. #2
    Senior Tuner edcmat-l1's Avatar
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    I've posted this before, I think in response to you. Make all the spark tables the same in that area. It will fix it.

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  3. #3
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    Quote Originally Posted by edcmat-l1 View Post
    I've posted this before, I think in response to you. Make all the spark tables the same in that area. It will fix it.
    It wasn't in response to me, but I did just see your post on this in another thread that I did not notice. I will give it a try. So when you say ALL tables, do you really mean every one of the timing tables?? Main Hi/Lo, DOD Hi/Lo, idle base and idle coast down?

    It seams strange that this is necessary. What is the trigger that causes the ECM to reference a different table if everything is steady state: rpm, g/cy, map, tps, iat, etc???
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  4. #4
    Senior Tuner edcmat-l1's Avatar
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    Quote Originally Posted by Michael_D View Post
    It wasn't in response to me, but I did just see your post on this in another thread that I did not notice. I will give it a try. So when you say ALL tables, do you really mean every one of the timing tables?? Main Hi/Lo, DOD Hi/Lo, idle base and idle coast down?

    It seams strange that this is necessary. What is the trigger that causes the ECM to reference a different table if everything is steady state: rpm, g/cy, map, tps, iat, etc???
    Yes. Probably not the DoD table, but hi/lo/idle/coastdown. Not sure why it references the different tables, other than at a certain TPS % it probably doesn't know if you're supposed to be in one or the other or the other LOL

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  5. #5
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    That sounds like a good feature request for the HPT custom O/S then! A toggle for telling the ecm when to reference the different tables....

    Thanks for the help Ed, I'll try this today and see how it goes.
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  6. #6
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    Even after matching the tables, the timing dip is still occurring. Not as often, but it has not completely stopped instantaneously pulling timing. This is at a steady state speed, throttle position, etc. But one problem I had matching idle and main spark tables, was that spark is too aggressive in the 1400, 1600 and 1800 rpm cells, as that is the same area in the timing table where this oddity is occurring.

    I think a better approach would be to find out what is causing the ecm to reference the different tables, and address this switching from table to table there.
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  7. #7
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    I think you and I might be chasing the same problem.

    http://www.hptuners.com/forum/showthread.php?t=39535

  8. #8
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    Yes sir, it does. I can live with cam surge that's caused by the cam itself, but this gdamn timing glitch, or whatever the hell it is, is really pissing me off. The car behaves like it's missing, but I know it isn't.
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  9. #9
    try logging Spark TqMgt Type , ETC TqMgt Type and other forms of spark retard or advance. Have you disabled burst knock?
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    I think I've disabled burst. Base vs. CylairDelta>zeors for V8. That was the only option that looked like it would disable it???

    In some areas, there is definitely a "sharing" of spark tables between base idle and main spark. Matched them got rid of that, but that's not the best solution, as now the main spark table keeps rpm too high as it transitions from higher rpm to idle speed.

    I will log what I can. I am now seeing about 20 deg being pulled intermittently coincidentally when fuel trims raise under steady state cruising.
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  11. #11
    Senior Tuner edcmat-l1's Avatar
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    Post up your latest tune, and a data log of it doing it. If you don't want to post it, email it to me. [email protected]

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  12. #12
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    Here you go.. Thanks for looking.
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  13. #13
    Senior Tuner edcmat-l1's Avatar
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    That's very strange. I can't see where it would pull that much timing from. Maybe try disabling spark under TCS method. See if that does anything.

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  14. #14
    please log the Spk TqMgt Type, if it says "Fst TqEx" i need to add some tables to your calibration.

    Also try disabling spark smoothing.

    Another thing you spark tabels are very weird at low RPM/load. The base idle and the main spark tables all should be similar so you don't get huge jumps when it transitions from main tables, to base idle or coastdown. I fyou log Spark State if will tel you which tables are being used.
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    The only PID I have available is Spark TQ Management. It does not say "type". I do have Spark State, and will take a log with that in the table tomorrow. I'm beyond my patience threshold to do more tonight. I logged missfire on all cylinders yesterday, and there was nothing.... But just to be sure, I'm also going to pull the plugs (again) to verify they are all looking good, and pull the covers off to check the rockers, hell maybe I lost a lash cap or something. It just acts like it's missing on one cylinder. I'm open to anything at this point.

    I know my spark tables are weird. They f'ing suck. The ecm continues to flip back and forth between Base Idle and the Main Spark table at low rpm/load. That's why Ed suggested I match them, and why they look like they do right now. I do not understand why the ecm would do that. Seams to me as smart as this thing is, it would know to not reference the idle tables if speed were above Zero MPH. If it did, then all would be golden!

    I am trying to add spark to the 1200 - 2000 rpm range, under 28 g/cyl load to reduce surge, but there are cells in the spark tables where idle and cruse mix - which is another factor to why they are all screwed up.
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  16. #16
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    Well somehow or other, by blind luck or divine intervention, I was able to get rid of those weird timing dips. I made several changes and I'm not real sure which one fixed the problem. I was going to experiment and figure out exactly what change I made resolved the problem, but figure I better not push my luck. God, I don't know how you pro's do this crap for a living.....

    I readjusted the main spark tables first, to what I wanted them to more closely resemble. Then the base idle table and the coast down table to get rid of all the huge steps I put there to match the main spark tables. I doubt this is what cured the issue though, but made the idle to dive transition the way it should behave. I disabled spark smoothing as suggested. No idea if this fixed it, but I ain't touching it and leaving it disabled. I then looked for anything that could just arbitrary pull 20 deg of spark, and the only thing that would do that was "Minimum final Spark TqMgt". I changed these values from -20 to -4. Then I changed "Minimum Final Spark Reduced Power Mode" from -15 to -4.

    The attached log is after I made these changes in the attached tune file. I'm pretty happy with how the car's running, but I am still fussing with two things....

    1) Hot start. It fires immediately, but then wants to nose dive. If I just barely touch the throttle, it will catch it before it stalls and will roll into a nice idle. I continue to raise start up air, but crap, I'm already better than double what I started out with. I tried raising cranking fuel, but that seamed to make it worse.
    2) Slight surge between 1500 and 2000 rpm at low lode cruising. Funny enough, it does not surge at all between 1200 and 1500 rpm. I suspect this is timing, but I'm unsure which way to go. 49 deg didn't help at all. I've gone as low as 38 deg, and that didn't do much good either. There's got to be a simpler way to find where to set this than experimentation.
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  17. #17
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    Reduce cranking fuel as it takes less fuel to start a hot motor.
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  18. #18
    Senior Tuner DSteck's Avatar
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    Disable spark smoothing. If you want the actual bucking to go away, then drop timing down to the mid 20s in the problem area. Depending on the cam, the bucking won't completely go away.

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  19. #19
    you need to make the top left corner of the main spark tables the same as the base idle spark and the coastdown spark tables. 40+ deg is way too much timing and will cause the cam surge, copy that area of the base idle table to the main spark tables and smooth the transitions around 1200-1800 rpm. It must be a smooth transition between the 3 tables when you are on and of the gas at light loads/low rpm.
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  20. #20
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    Quote Originally Posted by PGA2B View Post
    Reduce cranking fuel as it takes less fuel to start a hot motor.
    I did try that a couple tunes ago in the 190’ish ect range, and got KR in the order of about 6 deg when it would initially fire up. I will try messing with this again. I dialed it down 10%, I’ll try 5% and lower cranking spark a few degrees.

    Quote Originally Posted by DSteck View Post
    Disable spark smoothing. If you want the actual bucking to go away, then drop timing down to the mid 20s in the problem area. Depending on the cam, the bucking won't completely go away.
    I have been studying different logs, and noticed that engine torque goes up with a lower spark, so I suspect you are correct. I’m a bit frustrated with this, as damn near every book I have says to raise timing to reduce surge – including the tuning school guide I bought. That does not make sense to me, as at lower rpm, I can’t imagine why you’d want to advance spark. I will start working it down some more. Thanks…

    Quote Originally Posted by Chris@HPTuners View Post
    you need to make the top left corner of the main spark tables the same as the base idle spark and the coastdown spark tables. 40+ deg is way too much timing and will cause the cam surge, copy that area of the base idle table to the main spark tables and smooth the transitions around 1200-1800 rpm. It must be a smooth transition between the 3 tables when you are on and of the gas at light loads/low rpm.
    What causes the ECM to reference different tables Chris? And what exactly does the "smoothing" function do?
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