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Thread: AFR issues with 408 LS.

  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

    Default

    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
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    1,545

    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

    Default

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

    Injectors are stock LS3

  6. #6

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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???

  7. #7

    Default

    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.

  8. #8

    Default

    Quote Originally Posted by frostchevelle1 View Post
    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.
    So, update, got another o2 from MSD and problem is fixed. Just bad sensor.

    Why don’t you run in performance? My camshaft is definitely in that performance range.

  9. #9

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    My cam specs are below. This is a custom cam for a turbo 5.3. I tried running mine on the performance setting and it had stumbles and wouldn’t run correctly. Set it on mild and updated the software and works much better. I’m running 80lb injectors and 15psi at the moment. About to add water/meth and turn it up. LS engines are more efficient and the cams we are running are not really that aggressive.

    Lift .613 .617
    Duration @ .006 277 281
    valve timing @.050 INT 4 42 EXH 52 1-
    109 centerline
    Duration @ .050 227 231
    Lobe lift .361 .363
    Lobe sep 113
    Rocker arms 1.70

  10. #10

    Default

    Quote Originally Posted by frostchevelle1 View Post
    My cam specs are below. This is a custom cam for a turbo 5.3. I tried running mine on the performance setting and it had stumbles and wouldn’t run correctly. Set it on mild and updated the software and works much better. I’m running 80lb injectors and 15psi at the moment. About to add water/meth and turn it up. LS engines are more efficient and the cams we are running are not really that aggressive.

    Lift .613 .617
    Duration @ .006 277 281
    valve timing @.050 INT 4 42 EXH 52 1-
    109 centerline
    Duration @ .050 227 231
    Lobe lift .361 .363
    Lobe sep 113
    Rocker arms 1.70
    So I have a little bigger cam then you but very similar.

    After changing to mild, helped straighten things out a little, but car is still running fairly rich at idle, around 12:1. Can I change my MAP or TPS? I wanna lean it up.

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