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Thread: Troubleshoot surging at idle

  1. #1
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    Troubleshoot surging at idle

    Can anyone look at my data log and tell me what I have set up wrong to make my truck surge at idle?
    I attached logs of just idle when surging. I also attached a longer data log of driving because it does it when fully warm and holding rpm. Seems like I have a dead-band issue making the system hunt for O2. Cold idle when in open loop is pretty good. Hot idle after a driving has a clear hunting issue with AFR bouncing between 12 and 17.
    I haven't been able to get my autoprom to accept the 0-5v from my AEM gage, so that data is not there. - I am open to suggestions on getting that working too. I may just wire it to the B16 pin in the aldl as people suggest.

    Thanks for all the help so far. The truck is running much better now than it was after my "professional" tune.
    -It does run good during light acceleration. Its the cruising that it stumbles.
    Attached Files Attached Files
    Last edited by only_1; 4 Weeks Ago at 05:13 AM. Reason: Uploaded Bin File

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    Fuel Injected! sturgillbd's Avatar
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    I have been band-aiding the same issue for a while. There are proportional gain settings for the O2 at idle which can calm the idle surge down. Lower the proportional gain settings under O2 PID Idle Parameters in Parameter category view. I also lowered the number of counts in Proportional Counts vs. Slow O2 error to smooth the surging at cruise. This table is under Fuel Trim Parameters. There is also a table in there called Proportional Flow Gain Factor vs MAP vs RPM which has some effect on the O2 switching. I finally repaired my ostrich emu and hopefully the weather will break soon and I can do some more testing. I haven't been able to find a normal proportional gain setting in $0D for the O2 sensor. When you make changes, look at the O2 swings using Show Data Monitors to see the results of your changes. The surges are caused by the O2 gains and overshoot. You can see the surge in monitors while viewing live data. I usually turn on O2, BLM, INT and Calculated airflow since I added it to my adx file and modified my bin to show it. Some of the others may be able to chime in and have a better method. I have been trying to figure it out on my own. I run a Howards cam 180245-10 so my calibration is quite different from stock. I'll look at your datalog this evening.

    Hope this helps,
    Brian

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    That cam is a bit more aggressive than mine. I have comp 08-304-8. I don't know if it's the low injector pulse width? I also see that it's desired afr is in the 13's?
    I am ok with the 13's but didn't know if that makes it approach the edge of o2 tolerance quicker?

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    Fuel Injected! sturgillbd's Avatar
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    I just reviewed your idle log file and the idle timing is fluctuating a lot. The PCM uses timing to make fast idle changes instead of trying step the slower IAC valve. Can you post your bin? First thing I would do is adjust the throttle stop screw (minimum air) for about 10 IAC counts with the engine fully warmed up. I would also adjust the VE table to get the BLM closer to 128. You are sitting at 105 which is rich and the PCM is pulling fuel to compensate. If you still have surge, you may have to make changes to the idle overspeed / underspeed spark tables. I zero'd out the idle over/under speed tables to calm my idle surges down a long time ago. I could probably go back and repopulate the tables with some values but overall my idle is decent considering my cam won't have a smooth idle. Attached is a screenshot of the spark tables.
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  5. #5
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    I edited the original post to include the bin file. I have been updating the VE tables per the BLMs with the spreadsheet someone had put together (sorry, I forget who did). I moved the low rpm idle VE values down to offset that 10X numbers.
    Take a look at the Bin file and let me know if I am just wrong anywhere. Suggestions and criticism are welcome!

    Thanks for all the help!

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    Quote Originally Posted by only_1 View Post
    That cam is a bit more aggressive than mine. I have comp 08-304-8. I don't know if it's the low injector pulse width? I also see that it's desired afr is in the 13's?
    I am ok with the 13's but didn't know if that makes it approach the edge of o2 tolerance quicker?
    Didn’t realize you were the op. lol IIRC in another post you’re using 80#s with 20ish psi??? I’d like the experts to chime in on this one as I’ve yet to experience this myself. I too noticed on your log the small pulse widths of 0.xx at idle.

    What adx are you using? I couldn’t see the target AFR while viewing your logs.

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    Fuel Injected! sturgillbd's Avatar
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    I have came in late in the game obviously. If you have 80lb injectors and running them at 20psi, you have approximately 100lb per injector and you may have a little too much injector. You can try to lowering the minimum BPW times under BPW Limits. I don't know how much it will help you. I am running 61lb/h injectors at 27psi currently and idle fueling seems ok. Can you lower your fuel pressure? If so, you may have an easier time tuning this thing. Another thing I noticed is not a lot of spark advance at cruise. How heavy is this vehicle? I'll look at your bin this evening when I come back in.

    Brian

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    Quote Originally Posted by stew86MCSS396 View Post
    Didnít realize you were the op. lol IIRC in another post youíre using 80#s with 20ish psi??? Iíd like the experts to chime in on this one as Iíve yet to experience this myself. I too noticed on your log the small pulse widths of 0.xx at idle.
    Yeah with my injectors, at 20 psi I should be around 101 lb/hr for my injectors.

    What adx are you using? I couldnít see the target AFR while viewing your logs.
    I am using the 217_OD_v250 adx

  9. #9
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    Quote Originally Posted by sturgillbd View Post
    I have came in late in the game obviously. If you have 80lb injectors and running them at 20psi, you have approximately 100lb per injector and you may have a little too much injector. You can try to lowering the minimum BPW times under BPW Limits. I don't know how much it will help you. I am running 61lb/h injectors at 27psi currently and idle fueling seems ok. Can you lower your fuel pressure? If so, you may have an easier time tuning this thing. Another thing I noticed is not a lot of spark advance at cruise. How heavy is this vehicle? I'll look at your bin this evening when I come back in.

    Brian
    Yes, I can adjust the fuel pressure to be lower if that would help.
    The truck is a 1994 Blazer Fullsize. I think its around 4600 lbs.
    The spark map was something I got from Fast in my other post. I have not changed it much since I got it from him.

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    I am going to start over with setting the throttle body blades to idle with IAC closed when hot. I wonder if that isn't the part of my problem. Either way, some times its best to start over at square 1.

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    Fuel Injected! sturgillbd's Avatar
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    Twist throttle screw clockwise 1/4 turn. Look at IAC counts. Adjust only when hot. Keep turning clockwise until counts drop to around 10 or a little below in park. Shut off engine for approx 10 seconds (until PCM fully powers down) then restart. See what your counts level out at after a couple of minutes idling. Your counts weren't extreme but it needs a little more air past the blades. This helps the fueling at idle due to shearing action of air going past the blades. I am downloading your bin now and going to look at a few things
    Brian

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    Your datalogged spark doesn't match what is in the bin file. I have been trying to find what is causing the commanded spark advance to be lower than what is in the tables. Most places I checked it was off by approximately 5 degrees . I also notice your egr is commanded on the whole time the vehicle is running. I will dig further as I get time.

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    There is no egr on the truck. It is plugged off.

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    Would a vacuum leak cause these problems?
    If the EGR is always on, in the program, it would mean that the EGR spark correction would always be on right? So that would be the 4 degree drop in timing?
    -I zeroed this out for the next run to verify this, in addition made changes to try to disable EGR in general.
    Last edited by only_1; 3 Weeks Ago at 09:15 AM.

  15. #15
    Fuel Injected! sturgillbd's Avatar
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    Don't think you have a vacuum leak. Something is commanding the egr on and it seems like you have it disabled by scalars. I did a bin compare between your bin and BJYL and found several differences outside the defined parameters. You may need to start with a fresh copy using your timing tables etc .

    When replaying your datalogs, do you see the EGR being on all the time?

    Brian

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