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Thread: Help: Idle / Cruise Lean Issue

  1. #1
    Potential Tuner
    Join Date
    Nov 2017
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    3

    Help: Idle / Cruise Lean Issue

    Hello! First time poster, long time lurker. I have been having pretty decent success with tuning my first Gen 5 car. I have previous experience using Megasquirt on my Turbo Buick. I have a 2016 Camaro SS with LT Headers, no cats, Ported IM/TB, and a Rotofab CAI. I had a track rental in April where I ran 11.66 at 120mph. After the rental, however, I have been having this odd issue. At first I thought it was maybe bad gas, but after three full tanks, I decided that couldn't be it. The car will warm up normal with lambda climbing from 0.85x to 1.0 as idle rpm lowers. After a few minutes, it starts to go lean, sometimes climbing up to 1.15 lambda. Trims are all over the place with Bank 2 typically being much higher than Bank 1. Bank 2 seems to be pegged rich. I have replaced this sensor with a brand new AC Delco unit and the car has brand new plugs and wires. I thought it may be a misfire issue, hence the plugs and wires. It still COULD be I suppose.

    All plugs and wires seemed in good shape when they were pulled. I didn't notice anything abnormal.

    Before this issue, I had trims pretty close, being within 2% on either side. Fueling seems to be okay under throttle, but I have not been stepping on it much since I noticed this issue. Trims do not seem to change with VVE. Putting the car in open loop at idle, it goes even more lean. My WB was seeing 1.20 lambda. I shut it down quickly. I tried MAF only and Speed Density closed loop and nothing seemed to change.

    I am posting a tune and a log. If you have any thoughts, I would really appreciate any and all input. I am lost on what to do next.

    6.6.19 new o2.hplZNix Stock VTT Tables, VVE Adjusted Version 2.hpt

  2. #2
    Advanced Tuner
    Join Date
    Aug 2014
    Location
    Central, LA
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    363
    Which bank is your WB in?

    I'd swap the o2 sensors bank to bank to see if the problem moves. The way the bank 2 sensor is operating is odd.

  3. #3
    Potential Tuner
    Join Date
    Nov 2017
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    Quote Originally Posted by sevinn View Post
    Which bank is your WB in?

    I'd swap the o2 sensors bank to bank to see if the problem moves. The way the bank 2 sensor is operating is odd.
    The wideband is in Bank 1.

    The sensor in bank 2 is brand new from AC Delco, but I will switch it when I get some decent weather.

  4. #4
    I'm very new but did you change injectors and if so did you have good data? I had similar issues when I installed large injectors with little to no data. I was chasing my tail until the minimum pulse width and injector flow rate was close. Just sharing my experience in the hope it helps

  5. #5
    Tuner in Training
    Join Date
    Mar 2018
    Posts
    47
    It could be an exhaust leak or intake manifold lead or a bad injector.
    It is not tune related if you adjust maf to correct and with no effect.

  6. #6
    Potential Tuner
    Join Date
    Nov 2017
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    3
    Thanks for your thoughts everyone. The injectors are the stock ones that came in the car. I tested for IM vac leaks by spraying some starter fluid around the seals. I didn't hear any change in idle. Ill check the exhaust for leaks and swap the sensors when it stops raining this week. I was hoping I missed something in the tune, it would really suck to have a mechanical issue...

    Thanks
    ZNix