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Thread: Hard time tuning cold start idle.

  1. #11

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    Quote Originally Posted by 81 TransAm View Post
    What is your idle timing at?
    It's at 30° idle.

  2. #12

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    Quote Originally Posted by cwathne View Post
    It's at 30° idle.
    That seems a little excessive. Try 20° at idle and see how things work.

  3. #13

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    Here's how we got ours to cold-start nicely: (Using a laptop and scrolling live data so you see the "bubble" in the Config File tables.)

    Like said above, first you have to get the base fuel table idle area dialed in, also you want the Closed Loop operating so the system is using it's "CL Comp" (Closed Loop Compensation) to adjust things in order to meet the Target AFRs (which everything keys off of).

    My logic is that the Sniper system is adjusting to whatever Target AFRs you plugged in, no matter how well/poorly they make the engine run. And when cold, those AFRs may well need to be adjusted (offset).
    Therefore, the first thing is to get "Base Fuel Table" dialed in with a warm engine, then get the "A/F Ratio Offsets" dialed in, and THEN you can change the "Coolant Temperature Enrichment" percentages (to minimize the work that the "CL Comp" has to do in order to meet the modified Target AFRs. The examples below are from our stock 350 Chevy, no ignition control (yet).

    1. With a WARM engine (like after a short drive, not just idling until the coolant temp comes up) pull up the "Target AFR" table, and select the cells around where the bubble is appearing (the idle area).
    Make changes to those cells in = or - .2 increments, and watch the bubble. The goal is a Target AFR that the engine 'likes', as shown by a steady 'bubble' and the lowest kPa (highest vacuum). You should be able to find a range of AFRs it likes pretty quickly, generally shoot for the leaner side of the range

    EXAMPLE: Warm engine idles best at 650 RPM and 30 kPa with Target AFRs between 13.4 - 12.8. I'd set the Target AFR table from 600-800 RPM and 20-60 kPa to 13.2, just inside the leanest 'happy' AFR.

    2. Put the auto trans into gear, and watch the RPM drops, and change the Target AFR in those (lower RPM than stable in-gear or neutral idle) cells either leaner or richer, until the RPM drop going into gear is minimized. Find the rich and lean limits that the engine likes, this will help you a LOT later on with a cold engine not stumbling when going into gear.

    EXAMPLE: With Target AFR column at 500rpm set to 13.2, RPM drops clear to 500 RPM before recovering (and datalogs show it spiking lean). After testing various AFRs, engine likes anywhere between 12.5 and 13.0 - RPM drops to 575-600 RPM before recovering, recovers faster, and 'feels' stronger going into gear (and datalogs show much less of a lean spike). Set Target AFR in the 500 RPM column to 12.8, splitting the range difference (and leaving room for cold engine adjustment)

    3. With a DEAD COLD engine (laptop hooked up, datalogging ON), start the engine, wait for the "After Start Enrichment" to decay away (generally 30 seconds?), then make changes (like +/- .5 or .2) to the "A/F Ratio Offset" table at the respective Coolant Temperature points as the engine warms up, noting the engine response by either feel, RPM/MAP readings (or when fine-tuning by watching the 'bubble' moving around in any of the fuel tables). You might have to do this step a couple of times, since you're aiming at a moving target as the engine warms up.

    EXAMPLE: As coolant temps rise from 31°F to 92°F, the engine 'likes' AFR Offset of -.4 (which equates to a Target AFR of 12.8 while cold), then an Offset of -.3 until 123°F, then -.2 at 138°F, then 0° at above temps.

    4. This is a mix of Steps 2 and 3, but kind of a fire drill where a helper is nice. With a cold engine, start it up, put the engine in gear, note the RPM drop, then back into neutral/park, and change the "Target AFR" at the lower RPM or if that would put it outside the range established for a warm engine, change the "A/F Ratio Offset" at that temp. Then put it back into gear and see if the RPM drops more or less. Continue this fire drill as the engine warms up.

    EXAMPLE: Going into gear from 30°F to 60°F, the engine noticeably liked being richer by .4, and from 70-100°F it liked +.2, and above 100°F it was fine. The 30-60°F +.4 value would have pushed the 500 RPM Target AFR when warm to 12.4 (too rich), so I split the 'richness' between the Target AFR table and the A/F Offset, going to new Target AFR at 500 RPM of 12.6 (within the 'happy range') and Offset an additional -.2 below 60F, (giving an offset of -.6 at 60°F and below, or an AFR of 12.0 going into gear when cold, which seems to work well (I also try really hard not to go into gear and drive until coolant temps hit at least 60F, when the dash gauge starts to move.)

    5. Once you have good Target AFRs and Temperature Offsets, then you can datalog with a dead cold engine warming up, and later on make adjustments to the "Coolant Temp Enrichment" table based on the "CL Comp".

    EXAMPLE: This thread and This thread

    Also: Ignition timing is going to have a major part in this as well, but I have no experience with Sniper ignition control (yet). I suspect you would do a similar drill with the "Timing vs Coolant Temp" and "Timing vs Air Temp" tables as well, looking for the settings that the engine likes the best.

    I'll also pass on something I read here somewhere that helped me a lot, and that is: "no matter how bad it seems, you're closer than you think to getting it sorted out."

  4. #14

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    I've never adjusted timing for a cold engine, but I suppose it's another degree of freedom that a tuner has. Perhaps a little extra timing when the engine is cold would help. Something to think about I guess.

  5. #15

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    Thanks for all the answers. Regarding tuning my cold start, this is what I have tried.
    Cold start enrichment has been increased my 2% each day from a setpoint. This didn't take me anywhere.
    Then I reset it back to were I started, then decreased it 2% each day. This didn't take me anywhere.

    When I had my closed loop/learn active in my idle area even when hot, it had a hard time tuning it. My AFR is unstable at idle, engine acts really like you have a really big cam in it. Lumpy/ratty idle. So I tuned the idle with a with laptop connected. I have a CAN extension cable into my glove box, so I can easily switch from handheld to laptop. I tuned it by looking at idle vacuum and listening to the engine. Did the same with timing. So it starts to idle OK to good from 95°F and upwards. Hot idle is set to 750 RPM (that low mostly for that sweet idle big cam sound).
    Second reason I disabled CL, is that when cold and AFR shows lean, but really isn't. CL adds more fuel making it struggle even more. So my thought is that idle area even the rest of the table works great warm. Maybe by tweaking the cold start enrichment would kinda dial the idle better, but the best I get is not what I was hoping for running EFI. But I'm not giving up.

    Last reason for my CL/Learn to be off completely right now, is that one of my last trips with the car. I was on a HUB dyno, and the header gasket on #1 cylinder failed. So I disabled the CL/Learn right away from it to corrupt the fuel map I have today. This was of course after all my tries to get it to idle better at cold starts.

    Now, what it boils down to for me is two things:
    1. Hot idle set to low for the engine setup (warm 750 RPM). IAC seems small, and cannot get it to idle high enough when cold. If I help the idle higher to around 1200 RPM the engine seems to run good cold. But IAC only manages just shy of 900 RPM. So to get around this I can raise my hot idle, but that's something that I don't really want to.

    2. My cam is out of "timing" by a fair amount which results in poor idle performance. Engine is under its way out of the car, still waiting for the cam degree tool to arrive. When I have checked my cam placement and compared it to my cam card, I'll update.

  6. #16
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    Have you tried a spacer under the Sniper? If it's a distribution problem, it may help.

  7. #17

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    No, I have not. I do not have the hood clearance for it either.

  8. #18

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    Quote Originally Posted by cwathne View Post
    Thanks for all the answers. Regarding tuning my cold start, this is what I have tried.
    Cold start enrichment has been increased my 2% each day from a setpoint.
    Are you referring to the "Startup Enrichment" tables (which use coolant temp as one axis), or to the "Coolant Temperature Enrichment" table? Because the first set of tables only matters during starting and maybe 30-60 seconds later, and the "Coolant Temperature Enrichment" table matters after the engine starts and is warming up.

    Note that with Closed Loop turned on, if you're making changes to the "Coolant Temp Enrichment" table before figuring out what the "A/F Offsets" are, then any changes you make there won't matter because the CL Comp is going to be undoing your changes as it tries to get to the "Target AFRs" modified by those "Offsets". I'm still of the opinion that your best option (once you've verified cam timing and other mechanicals) is to turn the Closed Loop on, then focus on finding the Target AFRs and Offsets that your engine likes.

  9. #19

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    That's a good writeup you have above Bruzerbruce. I've been using your method the last few days while it's cold, for Dallas anyways. Mornings in the 30°s-40°s. Car starts real nice in the cold now. Even with a fairly aggressive cam in a SBC, 240°/248° @ .050, .595" lift it idles like a champ from startup to fully warmed up. Thanks for the info.
    Twin Turbo 400 SBC 748 RWHP in 1969 Chevelle.
    Super Sniper EFI, Edelbrock Victor Jr. CNC Ported heads
    Ported 2925 Super Victor Manifold.

  10. #20

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    Quote Originally Posted by bruzerbruce View Post
    Are you referring to the "Startup Enrichment" tables (which use coolant temp as one axis), or to the "Coolant Temperature Enrichment" table? Because the first set of tables only matters during starting and maybe 30-60 seconds later, and the "Coolant Temperature Enrichment" table matters after the engine starts and is warming up. Note that with Closed Loop turned on, if you're making changes to the "Coolant Temp Enrichment" table before figuring out what the "A/F Offsets" are, then any changes you make there won't matter because the CL Comp is going to be undoing your changes as it tries to get to the "Target AFRs" modified by those "Offsets". I'm still of the opinion that your best option (once you've verified cam timing and other mechanicals) is to turn the Closed Loop on, then focus on finding the Target AFRs and Offsets that your engine likes.
    I'm was talking about Coolant Temp Enrichment (my bad). I have also played with Startup Enrichment both in % and decay rates.

    Engine is almost ready to be lifted out, I did take off the headers. The side were my WBO2 was located, there has been two small leaks (very tiny). They were not visible before taking off the header. I don't know how much a tiny leak can influence AFR readings from the WBO2. Maybe small faults from different places might make a big difference in the end when I put everything back together. AFR Offsets might be a better way to tune in yes, when everything is 100%. Then tune the Coolant Temp Enrichment tables for the Closed Loop to work less.

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