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Thread: AFR issues with 408 LS.

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  1. #1

    Default AFR issues with 408 LS.

    Hey everyone,

    So first startup of new LS stroker, having some issues with AFR. The gauge inside the car shows 10.8 to 11 on startup by my atomic dash is showing 20:1.

    Attached are pictures of the dash. Let me know if anyone has some feedback

    Perhaps an exhaust leek or a bad sensor?? Thanks everyone.

    John

    9DBD3303-E266-4C67-B156-607C190CC2F9.jpg07492C39-6F3C-4D97-923E-408E45A8EE2C.jpg9B6C78A2-9B8E-4C72-AB56-6FA866F2557E.jpg

  2. #2

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    Quote Originally Posted by john.tempest View Post
    Hey everyone,

    So first startup of new LS stroker, having some issues with AFR. The gauge inside the car shows 10.8 to 11 on startup by my atomic dash is showing 20:1.

    Attached are pictures of the dash. Let me know if anyone has some feedback

    Perhaps an exhaust leek or a bad sensor?? Thanks everyone.

    John

    Attachment 4553Attachment 4554Attachment 4555
    Update here, swapped sides for both sensors and I am getting the same results.... any MSD help?!?

  3. #3

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    What’s your cam specs and injector size? What is your settings for cam? What sensor are you running for A/F besides the MSD?

  4. #4
    Join Date
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    Default

    If the engine is running, the MSD reading must be wrong.
    The OP has swapped his sensing over bank for bank, so the other A/F gauge must be more correct, and the engine is not the cause of the lean reading on the MSD.
    Gary
    Regards, Gary

  5. #5

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    Engine is running, but according to my other o2 sensor, very rich at idle, like 11:1

    Weird question, but on the original wiring diagram in the MSD installation manual for the o2 sensor from MSD it shows the sensor having 6 wires. When I look at my sensor, I have a 6 plug coming out of the sensor to plug into the EFI ecu, but only 5 wires from the plug to the o2 sensor???

  6. #6

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    I checked mine this morning and it only has 5 to the sensor itself but does have 6 to the plug. Do you have an option of trying a different sensor? I would probably tend to believe your LC2 over the MSD. And it will try and run rich if the MSD thinks it’s lean at 20:1. It’s trying to add fuel. But I don’t run my settings on performance either it gave me all kinds of odd readings.

  7. #7

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    So cam is a comp 227/243 113 lsa. I am set at performance. I have an innovate LC2.

    Injectors are stock LS3

  8. #8
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
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    Quote Originally Posted by john.tempest View Post
    So cam is a comp 227/243 113 lsa. I am set at performance. I have an innovate LC2.

    Injectors are stock LS3
    227 at 113 would be fairly mild in a 408.
    Short timing, low overlap for large capacity.
    Hence the high vacuum of 17 inches.
    For a performance street car, I would be running in the the 250s at .050 for 400 plus cubes.
    Gary
    Regards, Gary

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