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Thread: BMW X3 - 5.3L 6 spd with big cam, erratic idle

  1. #21
    Tuner in Training
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    Nov 2020
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    13
    Thank you again. Would you recommend that I use the smoothing function?

  2. #22
    Senior Tuner kingtal0n's Avatar
    Join Date
    Feb 2017
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    miami
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    which smoothing function, the one in the map that interpolates values? There is more than one way to 'smoothen' a map

    I try all of them and see what it gives me. If I don't like the way numbers are distributed simply "undo" that and try another way.


    Experiment and experience is the other 50% of tuning a computer. Once you remember how each feature works, it becomes very fast to tune and maintain a tune, Once you know the engine you will write most of the timing maps from scratch, then interpolate the values and clean it up manually using .00 or .000 increments of manual adjustment if it is available. In HPtuners make sure you increase the decimal portion so you can finely tune every cell.

    If you were asking about spark smoothing, the short answer is yes eventually use it to keep idle smoother.
    The long answer is:
    The first thing I do for a new engine when starting to idle tune process is remove all automatic helper features. Turn off the spark smoothing. Turn off the IACV controller, make it stay at 0 or low counts, if you have to unplug it. Make sure the throttle blade cannot move to disrupt your base idle speed. Make sure the engine is fully warm and ensure that any temp-related airflow parts are in their operating ranges for the idle (for example sr20det wax element in the throttle body should have it fully "closed" and warmed up with coolant).
    Then try to stabilize the idle by tuning without those helpers. Look for vacuum leaks and issues and see how good you can get the idle.
    Then turn those things back on and gradually increase their influence to a reasonable setting. Performance tuning of the engine idle is partially based on preference, so there is no solid set rule that says you can't allow a max range of IACV to interfere or not. Personally I tune so it can add a bunch of air if necessary, but is unable to pull much air from a baseline, and make sure I set the baseline high enough to just barely compensate for neutral idle. This way the IACV is just barely cracking open (very low IAC counts) during idle, so you have alot of adjustability in the upper range for more flow, and when you load it just off idle or going into 1st gear you want that IACV to be able to snap open to make the engine feel responsive and prevent it from stalling if the user doesn't really step on the fuel when they let out the clutch. Just off idle condition can be very strong and smooth if all these maps and iacv is tuned properly and prevent stalls.

    Before allowing spark smooth test and confirm the spark adders for idle dropping below target rpm or going over that rpm. Those maps are very important to smoothly subtract or add, as necessary. I use very small numbers in the first 60-80rpm range, usually less than 3* either way for anything under 100rpm is all that you need to move. Let the iACV and timing work together to control the idle but don't let either one of them adjust very QUiCKLY or ALOT at once. In other words you can slow down the IACV response and movement speed, and make it react more slowly, this will help on large cammed engines because you don't want the IAC to actually be moving at all during a stable idle.


    having a cam note typically will cost 140% to 230% more fuel at idle speed and make the advanced timing more profitable on the power stroke because there is a bigger squeeze
    In other words, stock 5.3 LM7 in gear I would use 11-12* but with a cam I use 15-17* because the pressure is lower (MAP in KPA is 55 instead of 45) the rpm is higher (620 range instead of 550rpm) injector duty cycle is about double and the engine is 'working' a little harder. So the mixture is more consistent because there is more air and more fuel. A really good injector can precisely meter the fuel and the result is superior idle quality when every injector is doing a good job of metering fuel.
    This is also where as a tuner you can make a choice, and either commit "hard or soft" for the idle quality. If you want the ride to cam in gear at idle you would pull fuel to about 15.2 to 15.5 A/F ratio in open loop. This will ruin the consistency of combustion because the fuel molecules are beginning to be too spread, more air will be needed so the compression will rise, and there are some partial misfires now. those misfires however slight alter the rate of change of the engine rpm, it begins to oscillate as misfires range in severity and the slight upward push from a still open intake valve as a decelerating engine with a big cam causes air to stall in some runners which contributes to a disruption in cylinder fill(if you slow the air in a runner it may have downstream implications as air begins entering the manifold in a pattern) and rough idle quality results, often forming a pattern of air pressure oscillation as rpm is also oscillating in some range.

    If you wanted a smoother idle you will tune towards 13.8 range, richer is smoother at idle. I try to limit my rich idles to 14.3 though because a rich idle will contribute to fouled plugs, carbon buildup, poor mileage. So i t is not recommended in cases where the engine will run at idle for prolong periods like a daily driver stuck in traffic. You really want that leaner ratio 14.8-15.2 to keep it from carboning up on gasoline as much.
    Last edited by kingtal0n; 12-10-2020 at 02:13 PM.

  3. #23
    Potential Tuner
    Join Date
    May 2012
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    1
    kingtalOn, Thanks for taking your time to share your experience. I'm just getting my tuner feet wet, I have been data mining this forum for gems like this. I appreciate the way that you spell things out, very refreshing.