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Thread: Stumbling After Cold Start

  1. #16
    Fuel Injected!
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    Jan 2017
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    I tried leaning out startup, and that didn't help. It wasn't any better when it was cold, and it was a lot worse hot. Is it possible this is moisture related? I realized I kept it in the garage in CA, but with it staying outside here I'm wondering if dew could be causing a problem.

  2. #17
    Fuel Injected!
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    I've noticed the coolant temperature needle is always in the exact same spot when it starts running rough. Does this just point to a bad spot in my closed loop AFR table?

    IMG_20190123_112910.jpg

    What would be the table to adjust for this - "open loop AFR vs temp" (0x45e) or "startup enrichment vs temp" (0x431)?

  3. #18
    Fuel Injected!
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    Lately it's been happening pretty bad, and I've been paying close attention to what it feels like.

    It seems that when I add throttle, I get a momentary surge of acceleration, but then it completely bogs. I've run a few maps with very little timing in certain areas, and that's exactly what it feels like. After a minute, even if I'm just cruising at part-throttle I can feel it surge forward (I assume when it enters closed-loop).

    Yesterday while it was running rough I noticed a pop from the engine bay while accelerating under maybe 60% throttle, which I guess must have been a backfire? It definitely wasn't just exhaust popping like you get under decel. AFAIK, backfiring can be caused by either a lean mixture or heavily-retarded timing, right? It's tough without the wideband hooked up (and I don't have time to put it on right now), but I guess I should just try adding some fuel on the warmer side of the open loop table, unless you guys have some other insights.

    Again, can anyone point me to the difference between "open loop AFR vs temp" (0x45e) and "startup enrichment vs temp" (0x431)?

  4. #19
    Fuel Injected!
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    Here's a new datalog. For some reason I didn't see it running super rough like usual, although right after startup it was wanting to buck a bit when cruising in first/second gear.

    The only change I made was increasing the "Closed Loop Proportional Step Size Gain Vs. RPM" (0x4D8) values by 10% across the board. Interestingly, cells 1600-2400 just reverted to their previous value due to the number encoding. (I also changed the "Injector Flow Rate for Instrument Panel" to fix my MPG readout, but I'm sure that is irrelevant.)
    Attached Files Attached Files

  5. #20
    Fuel Injected!
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    I was able to take a few more logs, and on the first two I'm certain I captured the problem. I haven't been able to log with someone in the passenger seat watching my phone, but I'm almost certain it occurs just before it goes into closed loop. Looking back to a log I took yesterday I believe it was running rich at that point - the O2 sensor shows about 850mV right before it drops into closed loop. This problem did seem to show up when I added headers, so I was wondering if I perhaps needed a heated sensor, but if my sensor were too cold I believe it should be reading a low voltage, not a high one.

    I'll drop the AFR a bit around 120 F and take another log as soon as I can. Although the weird thing is it's already tuned to run a bit lean in open loop - the table reads 97.3% change to AFR from 20 C all the way up to the top of the scale, which would mean it should be pulling fuel? I wonder if I have an exhaust leak that's throwing my O2 sensor off; I have been noticing my exhaust tips getting really sooty lately.
    Attached Files Attached Files
    Last edited by 90Vette; 02-03-2019 at 10:55 AM.

  6. #21
    Fuel Injected!
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    I once had an exhaust leak at the header collector coupling, because both my narrowband and wideband sensors were mounted near by they were being effected by the leak

  7. #22
    Fuel Injected!
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    Quote Originally Posted by Kitch View Post
    I once had an exhaust leak at the header collector coupling, because both my narrowband and wideband sensors were mounted near by they were being effected by the leak
    That's what I'm wondering. When I'm driving with the windows down, if I pass something that reflects my car's sound back to me it sounds like I can hear an exhaust tick coming from the left side.

    Exactly how much are you supposed to tighten the bolts on a header ball flange? I got them fairly snug, but I wasn't able to find a torque spec online, and I didn't want to risk crushing the ball flange.

  8. #23
    Fuel Injected! CDeeZ's Avatar
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    Crawl under it with it running and feel around the flange with your hands to see if you feel a puff of air indicating exhaust leak. If it's that bad you can probably hear it though.

    Sooty black indicates rich condition. What do the plugs look like? I've had to clean/replace a couple sets of plugs on the TBI I'm working on dialing in.

    And definitely get that WB on there. Will make it easier on you. The first time I put a WB on something I mounted it really close to the end of the tailpipe. The readings on the WB were all over the place from the atmospheric air that was getting to it.

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