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Thread: Idle's good but fluctuates while coasting

  1. #1
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    Default Idle's good but fluctuates while coasting

    I've got a 6spd and when I approach out of gear the idle fluctuates from 500 to 1500.. As soon as I get to a stop she's steady..


    I'll review the posts but if you info off the top I'd appreciate it..

  2. #2
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    Bump up your Running Airflow - aka Idle Airflow.

    Idle Airflow should be near your scanned MAF value (g/sec) at each temp range. jfPilla has an excellent writeup on this in the Tuning section ->http://www.efilive.com/forum/viewtopic.php?t=1169.

    Engine Calibration-> Idle-> Idle Airflow.

    Bump it at your operating temps to begin with ( +0.5 g/sec ?). Increase it until it "Cruise controls" a little....then back it down to stable. You will need to drive it for 30 - 45 minutes to allow for the Long term and Short Term Idle airflow trims to stabilize - between each value change.

    Hope this helps some.

    Cheers,
    joel

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    Just wanted to say that finally got my car back from the body shop and did what you said and it idles perfectly...


    Thanks!!!!

  4. #4
    Lifetime Member Aloicious's Avatar
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    okay, so I'm sorry for digging up this ancient thread, and I know both these guys haven't been around here for a while....

    but this is the exact same problem I have going on. is he actually referring to the desired airflow table here? i.e. raising it outside of the RAFIG process?

    here's whats going on with mine, at any speed, while coasting out of gear (M6), my RPMs will constantly fluctuate between 400 and 1200 RPMs. otherwise, when stationary it idles perfectly. I've done multiple RAFIGs and have the desired airflow table really good from about -4 through 92 ('good' as per the rafig process), I've logged spark, and done some corrections to my base spark table (to make sure a stable and constant advance is commanded in the problem areas, currently 28*), I've looked at TC and TF, made many many changes to those with little to no improvement, I've altered the under/overspeed correction tables for both airflow and spark several times, again no improvement. I'm working on the VE, its not perfect, but its not so far off that it would cause so much rpm fluctuation. sometimes it seems like something does help it, but then after a little while driving it just gets as bad as it was before. I'm going to do a nice log on my way to work today in a couple hours, so hopfully later I can post a log and tune for y'all to look at. I've read and re-read Sspdemon's idle turoial and tried all of that, nothing really helped my issue much, I also read Jfpilla's idle transition tutorial, and tried most of that, but changing the IAC effective area like is mentioned so that the IACDES_B matches DYNAIR, made the truck run horribly, stalling at every stop, etc. I'm about at my wits end with this.

    here's some info on the truck in question:
    1996 C1500 running a GenIe L31 vortec 5.7L, using LS2 coils with Mike's (eficonnection) coil near plug 24x reluctor setup, custom MPFI setup with ford (bosch) 39# blue giant injectors (flow'd and balanced) at 45psi, 12200411 PCM running a COS3 OS 02020003 (IIRC thats the OS #, its the cos3 OS for a '02 camaro M6 base tune), currently running OLSD (full OL, not semi-OL like the COS can do), ZZ4 cam (.474/.510 lift 208/221 dur, 112LSA), RHS torker heads (close to stock specs on the heads 1.94/1.5 valves, 170cc intake ports, 64cc chambers), intercooled L31 style whipple (side mount ones) with an air to water intercooler, it sees ~5ish psi peaks post intercooler (counting from baseline atmospheric pressure of ~85kPa where I live at ~4500 ft elevation), T56 M6....I think thats about it....

    one issue I know I will have, is with the side mounted whipple, the TB (and IAC) is moved quite a bit earlier in the airflow path, so with my setup, both the whipple, and the intercooler is after the TB (and IAC) which makes the already slow IAC corrections even slower. I've tried lowering the slower IAC RPM corrections, and raising the faster spark RPM corrections to compensate for this, but it really didn't make much of a difference with the issue I am having.

    it wouldn't bother me too much as it rarely actually stalls due to the fluctuations, but when it drops to 400rpm, my voltage drops and lights dim until it recovers, not good, and very annoying.

    any help is appreciated, I'll try to get a tune and log up later tonight too.
    1996 c1500 gen1e 5.7L - the "LS31", 24x CNP, LS2 coils, modified T56, 12200411PCM running COS3, zz4 cam, custom MPFI, etc. coming soon: Twin Turbos

  5. #5
    Joe (Moderator) joecar's Avatar
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    The link in post #2 got broken... does anyone have a link to that thread...?

  6. #6
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by bink View Post
    ...
    Idle Airflow should be near your scanned MAF value (g/sec) at each temp range. jfPilla has an excellent writeup on this in the Tuning section ->http://www.efilive.com/forum/viewtopic.php?t=1169.
    ...
    Quote Originally Posted by joecar View Post
    The link in post #2 got broken... does anyone have a link to that thread...?
    I found it, this is the fixed link: showthread.php?t=149

  7. #7
    Lifetime Member Aloicious's Avatar
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    Quote Originally Posted by joecar View Post
    I found it, this is the fixed link: showthread.php?t=149
    yeah, thats the one by Jfpilla that I was referring to about the IAC effective area screwing stuff up. (I also don't run a MAF at the time being, so I couldn't do ALL of what was mentioned in that thread)

    and just my luck I did a nice log on the way here to work, and it really didn't have the problem much, it would still fluctuate, but before, it would perpetually do it 400-1200 over and over while coasting, on this log it actually settles down to commanded idle after a couple swings. so something is going better.

    let me get my patients settled here at work and I'll post up the current log, tune, and an older log that shows the problem a bit better.
    1996 c1500 gen1e 5.7L - the "LS31", 24x CNP, LS2 coils, modified T56, 12200411PCM running COS3, zz4 cam, custom MPFI, etc. coming soon: Twin Turbos

  8. #8
    Joe (Moderator) joecar's Avatar
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    If you don't have a MAF, then you can use GM.DYNAIR instead...

    DYNAIR is the equivalent "airflow" computed from the VE table (as I understand it).

    Edit: grammar.
    Last edited by joecar; December 11th, 2009 at 03:47 PM. Reason: Typo

  9. #9
    Lifetime Member Aloicious's Avatar
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    Quote Originally Posted by joecar View Post
    If you don't have a MAF, then you can use GM.DYNAIR instead...

    DYNAIR is the equivalent "airflow" computed the VE table (as I understand it).
    good to know, I did log that in my log tonight, so you can see the difference between the desired and calculated. I've really been battling this lately, but tonights log shows the most improvement on it in the last 2 weeks or so. I've been working with the spark over the last several days, so that may be what has made the difference.
    1996 c1500 gen1e 5.7L - the "LS31", 24x CNP, LS2 coils, modified T56, 12200411PCM running COS3, zz4 cam, custom MPFI, etc. coming soon: Twin Turbos

  10. #10
    Lifetime Member Aloicious's Avatar
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    okay here we go, these are fairly long logs here, sorry for the size.

    attached is my most current log (12-11-09_to_work_idle.efi)
    this is the tune where I would still have fluctuations but they would eventually settle down to commanded idle. you can see how different my desired IAC airflow (GM.IACDES_B) is compared to my calculated air flow rate (GM.DYNAIR) which is kinda erratic at times and I think something within the DYNAIR which is causing the issue. some areas which show what is going on are frames (parenthesis used to separate frame segments for easier readability):

    (17040 to 17295) worst area

    (15523 to 15733), (10818 to 11102), (10232 to 10481), (9608 to 9848) these segments start off bad, but end up working their way to commanded idle

    (16314 to 16460), (14464 to 14676), (13700 to 13820), (8905 to 8985), (4800 to 4940), (3480 to 3560) these all show the problem, but are fairly minor examples

    that log was driven using the attached tune (12-11-09_coasting_idle_tuning.tun)....don't worry about the VE table, I know its not pretty, I've done alot of engine work recently and am still getting it in line, I'm also working on the KR too, but the KR isn't affecting the coasting problem at all.

    this is an older tune, (12-10-09_to_work_VE.efi) it shows the worst periods of the issue, though I don't know what tune this was driven with. you can see the good amount of spark variation which I have worked on between this and the recent log. this log was just for VE so alot of the idle PID's aren't logged in this one. the most pronounced areas that show the perpetual fluctuations are at TIMEs:
    18:42:10 to 18:42:38
    18:44:03 to 18:44:93
    18:51:57 to 18:52:40
    (ignore the CALC.BOOSTNVAC, the PID is written incorrectly for this log and its not calculating anything right)

    any help is much appreciated! though I think the spark alterations have at least started me on the right path.
    Attached Files Attached Files
    1996 c1500 gen1e 5.7L - the "LS31", 24x CNP, LS2 coils, modified T56, 12200411PCM running COS3, zz4 cam, custom MPFI, etc. coming soon: Twin Turbos

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