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Thread: 7747 ECM what BLM target number for Stoich 14.13 AFR?

  1. #1
    Fuel Injected! babywag's Avatar
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    7747 ECM what BLM target number for Stoich 14.13 AFR?

    So if stoich AFR 14.7 in bin has a target ~128 BLM...

    What would the BLM target be if you change stoich AFR to 14.13 in the bin?

    Searched a little, but when you add BLM to any search it brings up a zillion unrelated posts.

  2. #2
    RIP EagleMark's Avatar
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    Search has never worked for 3 letters and I'm working on a cure!

    Your still shooting for 128.

    In theory a stoichiometric mixture has just enough air to completely burn the available fuel. No fuel left, no air left.

    Contrary to most everything on Internet a narrow band O2 sensor does not adjust to 14.7 AFR and a Cat Converter does not work best at 14.7 AFR. Narrow band 02 Sensor adjusts to Stoich and Cat Converter works best at Stoich. Just happens that when these vehicles came out gasoline with no E or Oxygen enhancers was Stoich at 14.7 AFR

    Now most fuel everywhere is E10. A safe AFR for starting point of a tune is 14.1, there's still some controversy in my eyes as Internet has estimates from 13.8 to 14.3. Testing my fuel here showed 13.9

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  3. #3
    Fuel Injected! babywag's Avatar
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    What would cause BLM numbers to not coincide with AFR?
    Would an exhaust leak cause this?
    If I go off data logged BLM numbers and target to 128 on corrections to VE then it goes too lean.

    I've just about had it with this truck, it's become a major PITA to tune.
    Using known good parts, and now a WB controller to verify that it's too lean.

    I have 2 Jeeps both are AMC 360 engines.
    The other one runs fantastic and was real easy to tune compared to this one.

    Doesn't seem to matter if I use a NB or a WB o2 sensor if I target 128 it's too lean.
    Fuel pressure is rock solid @ 13psi, and the injectors are new.
    WOT and AE afr are acceptable, so seriously doubt it's a fuel delivery issue?
    I've checked for vacuum leaks several times, and can't find any.
    This is a 1227747 fuel only system that I'm trying to smog.

  4. #4
    RIP EagleMark's Avatar
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    Stop using AFR and start using Lambda! Make sure your wide band controller is set up for 14.13 AFR then set AD channels to Lambda on a 1 volt scale. Innovate LC-1 is .50 volt = .5 lambda and 1.5 volt = 1.5 Lambda. When your in closed loop you shoot for 1.0 Lambda. At WOT shoot for .84 Lambda. Lean Cruise 1.10 Lambda.

    0 to 5 volt scale will drive you nuts in Lambda or AFR.

    Lambda is the same for any fuel. AFR is not!

    For instance if your fuel is E fuel and your using the WB with factory settings the WB will say 14.7 CL. It's not, it is Stoich/Lambda 1.0 but closer to E fuel AFR rating of Stoich 13.8 to 14.2... see why AFR sucks and Lambda is King!

    Use the factory NB sensor to ECM. DO not use the WB simulated sensor for it.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  5. #5
    RIP EagleMark's Avatar
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    Would an exhaust leak cause this?
    Yes!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  6. #6
    Fuel Injected! babywag's Avatar
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    Quote Originally Posted by EagleMark View Post
    Yes!
    Well then there I have it(hopefully).
    A few months ago I noticed the familiar noise that may be a leak on the driver's side manifold.
    The o2 sensor bung is ~3" down from the manifold.

    I'll pull it/get it resurfaced, and see what happens.
    If that's not it, not sure what else the cause would be?

    I've got it tuned by fudging the numbers, so @ least the engine runs right and won't melt a piston.
    It was pretty damn lean! when I logged it on Sat. & much better this morning.
    Basically I converted w/ 120 BLM for a target, and it went from ~16.x AFR to ~14.x AFR
    Since I can't get the WB into the datastream have to guess a little.

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