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Thread: E38 idle tuning

  1. #231
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    You need to reduce spark correction in B5128,B5129, B5130 and B5131 (I just use the same in B5128/B5130 and same in B5129/B5131)
    Use B1844 ans B1845 to get the airflow corrections required.
    Play around with those tables and you should get what you are after.

  2. #232
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    I went through this thread yesterday and tried to use the procedure posted by hymey all in search of a better (smoother) idle and maybe dial away some light throttle surging in my car...but I think I'm misunderstanding what everyone means when they say to watch the TB start trimming when I'm dialing in the min idle air. My car is a stock bottom end LS3 with ported heads, 226/234 .600/.600 114 cam ground with 4 degrees of advance, FAST 102mm manifold. I've played with the NW102mm TB, but I'm so tired of fighting surging at very light throttle around 1500 rpm, I'm doing everything I can to fix it...so I put the stock TB back on the car...I figure if I can make it right with the stock TB, then maybe I'll try putting the NW102 back on.

    After that, I thought about it some more, and thought, why not use the same idea behind limiting B1651/B1652 to find values for B1829 as well. At first I maxed out B1829 and zero'd out the B1843 and B1845 (my car doesn't have B1844, but I think those were still the right tables, 2010 Camaro LS3/M6 12637084). I brought down B1651 and 1652 until I was able to get the engine to sit at 800 RPM and average 15 degrees of timing...I wound up with 0.8998 in both of them...which I thought was rather low...but it was working, with the correction tables zero'd out, timing was pretty solid and RPM was holding well too...but maybe I have a vacuum leak, I'll need to investigate that again this weekend, when I will remove the FAST 102 to check it out thoroughly.

    Once I found those values, I saved them, and then maxed out B1651/B1652, and put 8 into B1829 (the whole table) and fired the engine up again, and again, I kept changing the number in B1829 until I sat at 800 RPM and ~15 degrees of timing as an average...I wound up with 7.52.

    Does this seem like a logical approach?

    After doing this, I put B1651/1652 back to 0.8998, then added 0.04, which resulted in setting them to 0.9398, then I took the value in 800 RPM for B1829 and multiplied it by 0.8 (maybe this was too large a change)?

    I now put the OEM data back into B1843 and B1845, and then multiplied both tables by 0.5 (to try to make them less agressive), and the car started and idled on it's own...there was really no startup flare like I'm used to...in fact it seemed to be struggling to start...but the idle was great. When I revved it, it returned to 800 rpm beautifully from say a slow gentle rev to 4000 RPM, or a full throttle rev to 7000.

    I drove the car home, and I still feel some surging around 1500 RPM...maybe it's a little better, maybe that's just me wanting to think it's better :(...either way, this morning I got in the car to go to work, and it was cold (45 F in the garage, compared to 65 F ambient yesterday when I was tuning, and the coolant temp when I was tuning was around 195-197) an it wouldn't start...it cranked, was very very lazy/sluggish to fire, and stalled immediately...I throttled it and was able to make it start, tried to back out of the throttle slowly to help it find idle, and it still stalled...I had to get to work so I yelled at the car, got in my other car and left.

    Should I just try increasing B1651/B1652 to bring the cold start back, or should I try lowering B1650? I'm nervous to do that as I don't really understand what else it effects...I know that B1651/B1652 is the only MAJOR change I wound up making in the tune (my minimum idle airflow looks a lot like it used to) that seems to have killed the cold start...but what I've read makes me think that raising it back up too much will make the car surge worse at light throttle/low RPM. Stock B1651/B1652 were both set to 2.0645, and I'm way down at 0.9398...maybe I should try 1.25 or 1.375?

    I'm going to go home at lunch time in an hour and get the car (I don't live THAT far away, and I HATE my other car, especially on nice days lol)...I guess I'll try 1.25 first and see if it starts on it's own...it's not as cold as it was at 7 am, but it should still give me a better idea.

    I'd appreciate any insight/thoughts from others...I've been tuning for YEARS on older cars (old LT1's, LS1's, even older GM TBI stuff) and these DBW cars make me feel like it's my first day.

  3. #233
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    I brought the B1651/1652 values up to 1.5 and the car started...poorly but it started...stinks like fuel when it's trying to crank...never had that problem before. :(

    I'm lost.

  4. #234
    Lifetime Member swingtan's Avatar
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    My quick and simple method....

    With the FAST 102: Check all components, especially the runners. They have been known to come loose and you will never get it to idle in this case.

    With the NW 102mm TB: Just remember that the ECM calculates the effective TB area and uses that to work out how much the TB needs to move for a given gm/Sec correction. With the NW, it is significantly bigger than the 90mm stock unit. {B1650} and/or {B1701} may need adjusting for this TB.

    The rest of the idle tables I'd set to stock to begin with and do the following.

    1. Set idle speed to say 900RPM. Something fast enough to ensure it doesn't stall.
    2. Set {B1892} up around 9.0gm/Sec, better too much than too little.
    3. Bring the car up to normal operating temp and let it idle for a bit. Log the idle for a few minutes making sure exhaust airflow gm/Sec, AFR, timing, RPM, MAP, commanded spark and ETCTP are logged.
    4. Check the log and highlight the idle section, note the average spark timing and compare with the tune setting for idle spark. If the average spark timing is over the tune setting, then you need to add to {B1892}. If the average logged spark timing is under the tune setting, you need to reduce {B1892}. Don't worry about surge etc. yet, just get the average airflow right. Your 15' timing should be OK for this.
    5. Once the average timing is pretty close (within 0.5' of the tune setting) you can work on any surge.
    6. With {B1845} I'd zero out all cells from -96rpm to 96rpm, then select the -128RPM row and hit "smooth" a couple of times. Do the same for the 128RPM row.
    7. Use the Scan Tool DVT's to clear the learnt idle settings.


    That's how I normally do it and it seems to work pretty well.

    Here's a 408 stroker motor that would be similar to yours. This log it's idling on 900, but it can idle fine on 825.

    Click image for larger version. 

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    If you get into too much trouble post the tune and I'll have a look.

    Simon.

  5. #235
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    Yeah, that's my plan for the weekend with the 102...I'll pull it off and check it out. It's all hand ported, to match my heads, but when I reassembled it I did use blue thread locker on the screws for the runners...we'll see I guess.

    I've found with the 102mm TB on there, I HAVE to use 13 degrees of idle timing, can't run 15 degrees with that as that TB can't seem to close enough to bring the idle down with any additional timing.

    I'll see what I find...it's a work in progress. I upped B1651/1652 to 1.625 for now, and I also took 4% out of the cranking fuel EQ ratio table, and it's a good deal better about startup...I was actually pretty happy driving the car to work this morning. I would like to put the big TB back on...I don't think I gained much power with it, but it looks so nice with that manifold. When I previously had it on there, I ran B1650 higher (I increased it until I didn't need to change the minimum idle airflow numbers to idle the way the stock 90mm did)...but I took it off for now just to try to wrap my head around this better.

    Do you guys have trouble holding the engine just off idle with the pedal? Even with the stock 90mm on there, I can't seem to just hold the engine at say 1300 or 1500 RPM revving free in neutral. It's either up to 2000 or idling...kinda a pain, and I think is part of why I feel surges in gear at 1500 rpm at very light throttle.

  6. #236
    Lifetime Member swingtan's Avatar
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    For the NW TB...

    Setting {B1650} sounds like you had it close. For cammed cars I normally make this smaller with the stock TB but as the NW is bigger, I'd set this higher. Note that altering this setting may alter the behavior of {B1829} "Minimum Idle Airflow". You may need to alter {B1829} in line with {B1650}.

    Set {B1701} to just under max, this would normally go to 8191.9 so set it to 8190. There are times when setting some cells to max, they get detected as out of range. So I usually set them to just under max.

    Then try dropping {B2805}, {B2806} & {B2807} by 10%

    {B1651} & {B1652} "should" be over 2.5%, I'm currently on 4.5%. These are simply a soft limit on how much correction is needed to control the idle. They don't actually do any adjustment themselves. If you had these very low (under 1%) and the car wouldn't idle when hot, then I'd say you didn't have enough idle air. Having these set too low would normally result in very poor idle when cold as the ECM can't command enough airflow.

    As for the last point, that sounds like Throttle Follower. You can zero out the tables to prevent any follower from occurring. Surging is normally a combination of airflow correction and fueling. Low speed and light throttle put the engine in a condition where small adjustments on the throttle cause large changes in airflow, so lots of things come into play.

    Post a log and the tune.....


    Simon.

  7. #237
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    I zero'd out the throttle follower this morning before work and I'm pleased...I need to learn how to drive the car again lol...I actually have to use the gas pedal to rev the engine to start from a stop . Before I'd breath on it, and have to get out of the clutch fast or risk sounding like a teenager driving a fox body. Now I can just tip into the throttle and come out of the clutch and the car pulls away smoothly (gotta love that Exedy twin disc, makes a little noise, but it's smooth as glass as long as it's not REALLY hot).

    I forgot I had already lowered B2805/6/7 a while back by quite a bit, and it calmed a lot of the surge down. I had previously pulled some timing out of everywhere to try to combat the throttle follower problem...I bet that giving it back now that I've got those tables lowered will help the surge more too...forgot all about that.

    I'm not going to change anything else until I take the FAST 102 off and apart and make sure it's all ok internally...then I guess I'll decide where to go next. After that if I'm still having issues I'll post a log.

  8. #238
    Lifetime Member swingtan's Avatar
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    Sounds like you're getting there then.

    Simon.

  9. #239
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    Does B1602 affect Cranking Idle Air (B1832) as well? Or does it only affect the Minimum Idle Airflow (B1829)?

  10. #240
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    what timing do you have during the surging at light load, one thing I have found makes a MASSIVE difference to light load surge is timing. I call it tuning for driving around the supermarket car park with a cammed car you need way more timing than you'd think to achieve smooth progression at light load. Most tunes will run around 25deg at 1200 to 1500rpm, you actually need around 35 to 38 deg just in that light load area. Try it and you;ll find its a different car mate. Hope this helps
    "Just a tune > yeah right !!!! "

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