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Thread: DFCO and Deceleration Eleanment.

  1. #61
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    Hey Mark,

    Been a busy weekend. Got a couple logs to check out if you want.

    I have not gone over the "tobowl" log, but I do remember the knock counts being higher than what I expected, (about 25 or so).

    The "tohome" log was not too bad with a total of 8.

    I'm probably hung up on the knock counts, but I think it's because I am still confused by how the counts are being reported.

    If I understand correctly, everytime there is a knock via the knock sensor, the accumulator increases by one. When the accumulator makes it to 256 counts, then 1 count is reported from the ecm to TunerPro.

    Is that correct? If that is, then wouldn't 255x8 = 2040 total knocks be bad? I don't recall hearing that many, if I remember any at all.

    Also, I see that quite a few of the knocks occur during the 3-4, or TCC lock up when the monitor shows the RPM's dropping from about 2700 rpm down to 1500 or so. I think it's one of two things. Either the TCC lockup is set too late or I am having tranny problems with the 3-4 area of the tranny.

    I think it's the tranny and am waiting for pricing on some parts.
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  2. #62
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    The knock count rising on 3-4 shift or TCC lock is because of extra load while cruising at a high Spark ADvance and it takes a bit to reduce timing, it's not like this ECM is fast at anything... Do you have Burst Knock Enabled? This helps! Burst Knock is an anticipated knock for situations just like this. If it's already on, then have to back off the timing a little.

    when the monitor shows the RPM's dropping from about 2700 rpm down to 1500 or so.
    That's a big drop! Is it just a shift or just the TCC lockup or is the shift to 4th and TCC locking the same time?

    Not really sure if knock counts are 1 count or 256 = 1?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  3. #63
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    The BIN has "Burst knock" flag set.

    It seems that the knock occurs when the tcc and the tranny shifts into 4th, but am not 100% sure about that.

    Friend of mine that was an engineer with GM stated that the counts were 256 = 1, but that makes me wonder if noise that is not an actual knock is being counted because I'd think you'd hear those, especially if you are seeing more than a few total knock counts.

  4. #64
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    you're most of the way there on knock logic.....

    what happens is that the knock filter activates its "knock happening" signal any time that the noise the sensor is picking up on makes it into the filter and the filter considers it knock. now, how long the knock filter holds the signal circuit in the "happening" state, that is what causes the knock counter to run upwards. i think it runs at 32,768Hz on the C3? so, every time you see an increment of one of the MSB of the knock accumulator(which generally you'll only see that in the datastream), that is actually 256 "time periods" that the filter has held the line active. this is the equivalent of .0078 seconds that the knock filter has detected(or "detected") knock. the filter is essentially an op-amp with a bandpass filter in front of it. because of this, it has minimum reaction times possible, so that doesn't necessarily mean you were knocking for ~.008 seconds of a run, but that is how long the line was held at that state. the slew rate of the op-amp may make it look worse than it is, but it could also make it look better because of the same reason. the knock sensor has to generate a signal in the "knock happening" range long enough for the filter to change a no knock signal to a knock signal.



    long story short, if i only saw the MSB of a knock accumulator run up to single digit numbers over a typical run, i wouldn't be too worried. if you had an ECM with a fast data stream and could watch knock retard, you could ignore the knock accumulator entirely, every time you see any retard, the LSB of the accumulator was incrementing, whether you saw it on the MSB or not. this is why on the P4 and P6 units, you'll occasionally see a small amount of KR come up, but the knock count not move.

    MSB of 8 = somewhere in the knock signal active state for around 1/16th of a second over the entire run. not saying it isn't trivial, but it isn't "ZOMG, YOUR MOTOR IS TOAST".
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  5. #65
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    Robert,

    Would there be any benefit to running a scope to the knock sensor and the ECM input?

  6. #66
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    it's been done before, but not by me. one of the australian guys posted a thread on delcohacking a while back, he injected some signals on the knock sensor circuit and monitored the output to see what all the knock filter was capable of, had some really interesting results.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  7. #67
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    You have a link to that by chance?

    Thinking of dropping the MPH for the TCC lockup by a couple, and/or changing the Burst Knock vs. Coolant 85 celcius from 3.16 to 4.92.

    Thoughts?

  8. #68
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    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  9. #69
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    I feel too many people get caught up in the knock retard "LIE" of the knock sensor. That being said I felt my knock sensor in my Express was lying to me due to the lack of consistancy and the fact it was reporting more knock in 1st and 2nd gear than 3rd gear, despite running the same timing table and air/fuel ratio. I was also not getting any part-throttle knock with a leaner air/fuel ratio and alot more timing. I turned PE knock retard off and run 16* at full load at 1,000 rpm, 20* to 2,000, 24* to 2,800, 28-34* of timing above 3,600 rpm now. Big Express GETS IT now and showing no signs of detonation on the plugs. Basically I put the HO350/ZZ4 350/HT383/Ramjet 350 timing advance curves in my 0411 and my vortec head 350 LOVED it.
    Last edited by Fast355; 03-18-2014 at 02:12 AM.

  10. #70
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    I agree! Especially when we are talking of numbers in teens.

    When I have encountered real knock with this old ecm and could sometimes even hear ping/knock the Knock Accumulator was spinning! Just like data with the knock sensor not hooked up. I've also seen it spinning up the numbers in $0D when knock circuit was not wired correctly or something else wrong like using a G1 adapter and chip but not connecting the Memcal...

    One project I never got to with $42 was add another patch to replace something with Knock Retard timing. This would at least show if the few knock counts were acually knock that was real and making the retard work.

    WIth some newer PCMs and especially OBDII fast data stuff you can watch the knock in monitors and see if it's real knock or noise by the shape of the line in monitors. A jagged sawtooth is knock and a smooth hump is noise...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  11. #71
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    Now I guess I am down to trying to understand what is real knock and what isn't.

    As seen in this log at time 5:28 to 5:38, there were 4 counts and looking at the monitor at the time they occurred, I can't see anything that may have caused it other than the possibility that the timing in that area may be on the verge of being too much. I don't know.

    Mark, take a look at time 6:53, the INT dropped to 96. I don't think that is a concern, but thought I'd point it out.

    The bin is the sv3f.
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  12. #72
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    Quote Originally Posted by damanx View Post
    As seen in this log at time 5:28 to 5:38, there were 4 counts and looking at the monitor at the time they occurred, I can't see anything that may have caused it other than the possibility that the timing in that area may be on the verge of being too much. I don't know.
    Your still not totally warmed up there and around 160*f. Not sure if there's any spark/fuel/etc.. going on that close to warmed up?

    Watch your spark advance table with data tracing on! It shows, as well as TPS% you were slightly decelerating and when doing so spark advance was going up. Although knock counts usually occur under load, it can happen anytime, like this! Like I said in the beginning when I put this 3.4L Spark into your bin I thought it may be a little to much for a truck.

    I would take out 2-4 degrees from that area.

    The INT dropping 96 to 6:53 is a nice sloped steady drop while you were decelerating and nothing I'd worry about.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  13. #73
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    Just a quick update, the past 4 days have been pretty busy.

    Looks like the gas mileage has gone up a little bit. Based on the fill it up/devide by mileage formula, it appears that if I keep my foot out of it, I am about 22.5 to 23.5 from 20 to 21.

    Mark, I backed off the spark in the coolant comp table another degree and so the knocks at low temp seem to be taken care of.

    I also dropped the spark in the higher load areas 1 degree and that seems to be working pretty well also.

    I will post some logs of the latest revision for review later.

    When I get the spare transmission rebuilt, I will revert back to an earlier version of this bin and do some logging. I could be wrong, but I think my tranny in the truck is probably not in optimum shape.

    One last question, any recommendations for plugs and wires?

  14. #74
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    Good deal you tweaked a few more MPG!

    Control of the foot has a lot to do with it!

    I always stick with stock factory spark plugs. Wires? Whatever good quality that is on sale...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  15. #75
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    Been a couple of weeks since I've last logged, but the knock counts are climbing again, with nothing been done except driving.

    I've got all the parts and am ready to start the rebuild on the spare tranny, hopefully this weekend.

    I think the current tranny is causing me a lot of grief.

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