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Thread: Sniper idle repetitive overshoot & undershoot.

  1. #11


    We can't help you without a Config File and a datalog.

  2. #12


    Quote Originally Posted by hitdave View Post
    The problem starting at 1000 RPM seems significant. Idle is set to 800 and Re-enable Idle Control is set to 200 above idle. It seems likely that idle control resumes at 1000 RPM and triggers IAC opening that I don't think should happen.
    I don't have answer, but just wanted to say you're not alone as I believe I'm battling the same behavior with my Ford 289/manual transmission during deceleration.

    What I see is a couple contributors for discussion/question from my end:
    Upon first deceleration the IAC ramp down occurs, but upon the next downshift without touching throttle the IAC immediately goes to zero and does not ramp down. So when I push in the clutch at full stop the IAC then shoots open trying to save it, but can't and car dies with the datalog showing massive lean condition. What I think is happening is without touching the TPS, the IAC doesn't know during the second downshift that it should begin the ramp down behavior again. It probably thinks the idle inexplicably shot up which is why IAC goes to 0% during deceleration.

    Quote Originally Posted by hitdave View Post
    Also, I've smoothed the Base Fuel Table in the idle area. I also tried adding fuel and later tried subtracting fuel in the idle area. Each time the Learning function subtracted fuel after I manually added and added after I manually subtracted.
    I'm moving away from updating the Base Fuel Table for now and focusing on the interaction with AFR table. If you adjust the Base Fuel Table and not the AFR the ECU will compensate to try and match the AFR table when in Closed Loop. In the laptop software I'm using the more elaborate table AFR setting rather than the simple Idle/Cruise/WOT default option to try and focus on the deceleration/return to idle area.

    What further complicates this is that in my case under deceleration the ECU goes into Open Loop and uses only the Base Fuel Table so regardless what I do to the AFR it may not be doing anything most of the time during deceleration. At least in my case, when the IAC shoots open and the engine dies it has just re-enabled Closed Loop and seems to be trying to match the AFR table. So I'm trying to get to a spot where the AFR and Base Fuel Table are similar under deceleration so there isn't this jarring adjustment made at the last second.

    The IAC values gradually decline. AFR remains constant. I think that's as expected, but it changes at 1000 RPM. At 1000 RPM the IAC values increase and fuel flow remains constant.
    Check if the ECU is going into Closed Loop at that moment, that's what's happening on mine.

    Now when in the Base Fuel/AFR maps the mixture needs to be lean and then enriched for idle is what I'm trying to figure out. I've got it where my car won't die warm, but still dies every time while cold. It's like the IAC ramp down doesn't kick on at all when cold, which I'm wondering if has to do with the higher idle/ramp down settings which I'm going to try adjusting next. I feel like I have my setup good for warm and just need to figure out how to compensate for cold temps to get same result. I finally got the USB cable for my laptop to make adjustments faster. Trying to troubleshoot the cold issue when it warms up after just a few minutes has been very time consuming.

    Anyways, not any answers here, but I hear you on this issue.

    EDIT: And other areas I've played with are bumping up the Minimum Injector Pulse Width, which completely cured the car dying when warmed up, but didn't help cold at all. I currently am trying to fix with that setting back at default of 1.2 as shouldn't I be able to enrichen the right area to get the same behavior as extending the minimum pulse width?

    I also went into the Advanced ICF software features and tried adding a table to Offset the IAC based on MAP which was interesting, but seemed kludgy and a workaround.
    Last edited by Varnish; 05-29-2020 at 05:30 PM.

  3. #13


    Follow Danny's links on how to upload the GCF and datalog and we'll help.

    Sounds to me like you have the Idle ICF and possibly other tables out of wack.

  4. #14
    Join Date
    Dec 2009

    Default (Holley Sniper EFI Retrieve, Save & Upload GCF - SD Card & Laptop/PC Usage, Pages 72 & 73) (Related Forum Thread)

    Originally Posted by Danny Cabral
    For further assistance, post your Config File and a short datalog of this occurrence for us to analyze.
    Also, review the datalog and inform us of exactly where in the datalog (time/seconds) the problem occurs.
    Datalog & Global Files can be linked to a document hosting website. I use
    Files can also be "zipped" (compressed zipped folder) & attached directly to a forum post ("Go Advanced" & "Attachments").
    Your Config File is in the "Documents", "Holley" folder, "Sniper" folder, "Config Files" folder (.hefi file).
    Your Datalogs are in the "Documents", "Holley" folder, "Sniper" folder, "Data Logs" folder (.dl file).
    Someone will analyze/troubleshoot the problem & offer advice. (How To Record & Email A Datalog)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  5. #15


    Here are OneDrive links to Sniper Config File and datalog files. Hopefully datalog is pretty straightforward, as it's several seconds long and shows three consecutive idle RPM undershoot & overshoot cycles. Thanks, Dave.!AqLjjgvIcUxF1C4p...K4Jv8?e=URTUCn

  6. #16


    If you can attach them here through the Sniper forum, I'll take a look.

  7. #17


    I can't read your Config File for some reason. In the datalog, it appears that it starts to die (MAP increases) and then it tries to recover from that situation. Hard to say for sure, but it seems like you're trying to run it too lean at idle for your engine. I think that if you move your Target AFR to about 12.8 to 13, you can see if a fatter idle settles it down. I'd do this live rather than through files. Also, your voltage/battery levels are marginal. They vary from 12 to about 12.4 through this. Not sure if it'll behave better if you raise your target idle RPM as a test. But I think you'll have better results if you can identify and correct your low voltage condition.

  8. #18


    The attachment is a zip file with Config File and a datalog. The datalog is only several seconds and shows three cycles of under and overshoot. One of the odd things is fast IAC spike at 0.5 seconds. One thing that I don't show in the datalog is that after several cycles the engine returns to a nice idle. It's as if something (IAC opening?) happens too fast and then recovers and overshoots. On the handheld I see the same thing. Idle goes too low, sometimes stalls, and then goes a bit too high. When this happens I can see AFR go way too high at the point that idle RPM is too low. Also fuel delivery during ramp down does decline, but it's gradual, which seems OK.

  9. #19


    Can we see the datalog of it idling correctly? Without knowing it does sometimes idle correctly, my first thought is to block the IAC inlet off and get it to idle with just the throttle plates and tune the Target AFR and the AFR, along with timing and see if I can get it to purr. After that, reintroduce the IAC motor and that will tell you if you have a IAC motor circuit problem or not. It does appear as if the idle area is way too rich as of now.

  10. #20


    Hi abc. I've attached a datalog of a smooth idle. It ain't perfect, but it's pretty good. At best, it's a similar repetitive cycle, but so minor it's hardly noticable. At worst, it fluctuates a lot and stalls. It's always idles better at full operating temperature than when cold. Thanks, Dave.

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