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Thread: Individual Cylinder Trims Discussion

  1. #16
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by steveo View Post
    warmer air is less dense. humidity also plays a factor. warmer air requires less fuel. the IAT temperature compensation is imperfect. it's normal for trims to change during things like weather fluctuations.
    I knew / know this happens and I've observed it, but I was a bit in freak out mode because it felt like it was running extremely lean and this is a new / replacement MAF sensor. I killed the 22 year old AC Delco cleaning it, and I had no reason to be overly confident the replacement would be identically calibrated.

    I wish I'd noticed the EGR trying to enable sooner, it would have explained a lot. I assumed setting the enable RPM as high as possible and disable at 0 would kill it completely, but it still attempts to enable and adds spark before switching off.

    Edit: I wonder if it would be worthwhile patching the EGR out completely, so as to save a few CPU cycles?

    Quote Originally Posted by steveo View Post
    don't get too OCD about keeping your trims perfect. let closed loop do SOME of the work. that's why it's there. otherwise just turn it off like i usually do
    I do understand we're trying to re-shape the VE tables, not necessarily have BLMs at 128 everywhere. I guess the goal is to either log only in ideal conditions (still trying to determine what exactly that is) or have equal amounts of logging in extreme conditions and let the law of averages find the middle.

  2. #17
    LT1 specialist steveo's Avatar
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    Quote Originally Posted by spfautsch View Post
    I wish I'd noticed the EGR trying to enable sooner, it would have explained a lot. I assumed setting the enable RPM as high as possible and disable at 0 would kill it completely, but it still attempts to enable and adds spark before switching off.
    could be a testing routine. 'vette calibrations have lots of extra tests to feed those pre-obdii pids. try disabling the egr error code and see if it goes away. with that cam an egr is kinda pointless, might as well just block it off, if for no other reason that it's ugly.

    edit: often disabling the error code disables the test routine too. egr test involves popping the egr open for a moment during conditions when it's not usually operated, but it's unlikely the driver will notice and when vacuum is steady, and monitoring MAP for a slight drop in vacuum.

  3. #18
    Fuel Injected! spfautsch's Avatar
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    I just did that, hoping to flash and log tomorrow if the forecast pans out. Zeroing the spark adder along with smoothing out a degree of timing at the margins of this range seemed to make a big difference yesterday evening. It's very noticeable when you get into the hot air on the interstate. Am I ever glad I hadn't detuned knock retard.

    Block off plate is ordered - I knew the cam would create boatloads of natural EGR but left the valve on for inspection b/c Missouri's rules want the emission devices to be there. They don't care if they're working but by the letter are supposed to be visible, so in emissions exempt counties like mine we have a lot of folks driving around with gutted cats that the inspectors can't say a thing about. It won't need inspection again until 2019, and after that I can register it as an antique vehicle so no inspections required.

  4. #19
    Fuel Injected! spfautsch's Avatar
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    Disabling the error code(s) didn't make any difference, the ALDL data shows the egr duty cycle toggling from 0 to 12.5% and back to 0 frame after frame. It's a weird quirk but I've disconnected the solenoid so it's no matter.

    Didn't resolve my issue anyway.

    I think it might be a high pitched exhaust droning / resonance I've been hearing for a while, seems to only do it when the exhaust is hot. I noticed it this morning with the windows down at a low enough speed, and happened to be looking at the knock count at the time. Very odd, almost sounds like if you were to let the air out of a balloon while stretching the neck so it squeals. I didn't notice it at all when I made a short log yesterday (with fairly low knock counts) but my wife was with me so the suspension and chassis could have been settled differently.

  5. #20
    Fuel Injected! spfautsch's Avatar
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    After finding a "smoking gun" cracked exhaust tip that was surely the cause of the goose-pitched exhaust drone and welding it up I'm sad to say not much has changed. I'm going to move my (false?) knock issue to a new thread so as not to steer this thread even further off the title.

    I did however want to report that on a whim I added some individual trim to #1 as it was reporting weakest on the eehack cylinder balance test, with decent results.

    Quote Originally Posted by steveo View Post
    since you have shared vacuum in the manifold, the cylinder drop approach is a great method

    of course perfect balance at idle isnt super critical, and as soon as you open the throttle plates, all hell breaks loose anyway.
    My thinking was that a possibly leaner cylinder was exacerbating a possible lean swing condition in cruising cells, causing knock. I haven't completely ruled out this possibility, but I did greatly lower the individual trims tps limit so it shouldn't be an issue in any realized load range.

    Beyond that, my main concern with cylinder balance is how individual trims might affect cell 16 and any BLM split there. I've completely revised my timing tables, so most of my logging data in regards to that has become more or less invalid. However, I'd love to hear thoughts on the value of making the sum of the indvidual trim banks add up to something close to 4 and 4.

    Whatever the case, if the worst idle split I see is 4-6 counts as observed yesterday I'll have no problem calling that "good enough".

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