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Thread: MegaSquirt II A/C Idle Up Modification

  1. #21
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    825

    My VIN:    767 (3.0L EFI/EDIS)

    I did a bit of tuning, and got the idle AFR good (as in, in the vicinity of 14.7) down to about 600 RPM. There were little things I had to figure out, like that when you turn off idle control, you also need to go into test mode and force the IAC closed or else it will just be stuck at the last position it was. Small stuff that's really obvious in retrospect.

    Anyway, the RPMs drop down to the high 500s, but they recover without a problem. That said, I did manage to stall twice today, the first time I stalled since I did these changes.

    Of course I wasn't logging when the first stall happened. I hit the gas from a standstill, then slammed on the brake when I realized that I couldn't make it through the intersection. It started up easily enough. The second stall I was logging, and happened when I was about to try to reproduce the stall.

    I noticed the IAC was open at around 30 steps at idle, so I gave the screw a quarter turn to bring it down to 15-20 steps a minute or two after the stall. I'm hoping that by not allowing it to close completely that I can keep it from stalling, which I think is what FABombjoy was suggesting. However, I've noticed that after enough driving, the IAC will read 0 steps but the idle will be around 1000 RPM. I believe that MS thinks the the IAC is closed, but it's actually not closed. If I turn the car off and on again, the idle goes back to 790 RPM and the IAC goes back to around 15 steps.

    Now, I know that it's calibrating to completely closed on startup. It just seems to be losing the calibration the longer the car is on. I tried increasing the minimum steps from 1 to 2, in case that had anything to do with it. I'd like to close the IAC more, but I need it to behave more reliably before I do that to keep the idle down.

    Anyone else have this problem?

    The log has three marks at the point where it stalled (around time 5421 is the stall). Near the end of the log you can see a high idle while the IAC is closed. I then turn the car off and on again and the idle goes back to normal and the IAC is a bit open:
    2019-09-10_07.38.21.msl.zip

    Tune:
    CurrentTune.msq

    Thanks!

    -- Joe

  2. #22
    EFI Squirted DARCOM's Avatar
    Join Date:  May 2011

    Location:  San Antonio TX

    Posts:    74

    My VIN:    2942

    I have always had a similar issue. But i have megasquirt set at 900 rpm so it adjusts automatically to target that rpm in msextra.

  3. #23
    '82 T3 FABombjoy's Avatar
    Join Date:  May 2011

    Location:  Lansing, MI

    Posts:    877

    My VIN:    10270

    https://imgur.com/a/8CoiYdu

    That seismograph looking section is an oscillation. Like a guitar string or a bell.
    Oscillation in EFI logs means something isn't set up correctly. K-jet oscillates and we should be better

    As you go from bottom to top, numbers should almost always increase. Your 600/740 columns have:

    72 73
    60 70
    60 70
    69 69

    This is a setup for oscillation and you can see it in the AFR and consequently the MAP & RPM. All over the log at idle speeds.

    Idle steps: Not sure what the magic setup with your valve will be. The jeep valves used on many MS setups do prefer to move in 2 step increments. I also have Power Between Steps to "Always On". The valve runs warmer but the # of steps vs actual opening is consistent.

    The goal with your base opening should be almost your preferred idle RPM when warm.
    If you set it up so your IAC reads 0 steps at your preferred idle then may encounter times where the idle is too high to control with the IAC. That's been my experience anyway.

    Also, idle correction advance is triggering at times it probably shouldn't be and pulling up to 8 degrees of timing. I would turn it off until TPS is working.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

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  4. #24
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    825

    My VIN:    767 (3.0L EFI/EDIS)

    Oscillation: Ah, thanks. Now the question is, do I just drop the lower MAP cells (below 35) to below 60, or raise the 35 and 40 MAP cells up. Since I tuned those two cells ~14.7 AFR to 60 VE, I'm guessing I should drop the <35 MAP cells down.

    IAC: I'll give Always On a shot first, then increase the minimum steps if necessary. Thanks!

    Throttle plates: I'll close the plates a little more today, then seen how the IAC manages with Always On set. I'll try to get the plates as close to holding just under idle on their own without the IAC.

    Idle Advance Correction: Turning that on seemed to help with seeking at idle. I'll look into building a pedal-mounted version of a TPS, since the throttle mounted one just doesn't want to work for me.

    Thanks again!

    -- Joe

  5. #25
    '82 T3 FABombjoy's Avatar
    Join Date:  May 2011

    Location:  Lansing, MI

    Posts:    877

    My VIN:    10270

    Quote Originally Posted by jangell View Post
    Oscillation: Ah, thanks. Now the question is, do I just drop the lower MAP cells (below 35) to below 60, or raise the 35 and 40 MAP cells up.
    You don't want big gaps. The injector PW is connected to the VE number on the table but also an interpolation of the surrounding values based on a weight of how far the RPM is from the target column. Big differences in any surrounding cell will have an affect.

    Serious and honestly no-insults-intended question: What materials have you studied regarding EFI tuning?
    I get the impression that you're figuring things out as you go and relying on internet searches / advice. This would be a recipe for continuous frustration.
    I only ask because those out of sequence values are a glaring fault in the idle zone but I get the impression that your eyes aren't trained to recognize it

    Have you read any books on the subject on tuning EFI, specifically speed density tuning? This might be a good start:
    https://www.amazon.com/Designing-Tun...dp/1932494901/
    There might be a collection of resources at your local library, too.

    Years ago I started by using internet exclusive resources. Then I read several books on the subject and realized that the internet tuning resources are lacking a comprehensive, approachable learning resource.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

    Console5.com - Game console parts, kits, games and more. [shop] [wiki] [RSS] [f] [t]

  6. #26
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

    Posts:    825

    My VIN:    767 (3.0L EFI/EDIS)

    No offense taken, and your impression is correct -- I'm basically figuring it out as I go along. I've done a lot of googling and hit various forums and sites explaining things, and the theory of operation from the MegaSquirt docs. I was extremely confused for the first few months before I actually had the car running, since I really had no idea what any of this looked like on a running engine. I also tend to focus too much on the wrong details, though, which gets the car into feedback loops. For example, these out-of-sequence values are because I was super focused on the specific cells I was tuning at that time, and didn't look around them, in part because I wasn't hitting them, even though I know that it's interpolating from the four cells closest to the current engine state.I've also seen what ideal tables look like, but the gap between "ideal" and "what works for my car" is unclear. The large number of variables and somewhat opaque settings are making it more of a black box than I'd like.

    I know things like not wanting big jumps, and earlier I had cases where auto-tuning would create fuel cells that were distant enough (just by like 5-10 steps or something) that the car would slightly buck as it oscillated between those two cells. But it was easy to hold that MAP and RPM while the passenger tweaked the reduce the jump. The way idle runs around and the randomness off the stalls frustrates my attempts to fix it.

    I'll grab that book. I admit that although I do try to use internet resources for many things, I find that they are very good for computer programming, and much less good for everything else, at least with regards to adequately learning how to do things on your own. That doesn't stop my from trying, though.

    I should also be clear that I don't want to say, "I did this, here's my logs, can you guys tell me what setting to change next?", although that does feel like what I'm doing a lot of right now. I want to understand what the settings do and how to fix these problems myself without basically being a human telepresence robot for you guys to do the fixes for me.

    I just bought that digital version of that book and I'll start going through it. Thanks again for all the assistance!

    -- Joe

  7. #27
    "Former Delorean owning Guru" Spittybug's Avatar
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    Every now and then look at your tables in 3D. They should look like nice gentle waves of grain........not roller coaster rides.
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