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Thread: Idle AFR changing whilst Idling

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  1. #1
    Fuel Injected! Terminal_Crazy's Avatar
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    Idle AFR changing whilst Idling

    Hello
    I've been running the car all morning flushing out oil from the coolant.
    It's running an OLSD tune at the moment still set at 13.0 :1

    Car starts at 10 and sits around 12.5 .

    Occasionally when i've checked the temp, the AFR is around 15 then later back at 12.5.

    It fluctuates about 0.5 point either side any way, but why should it decide to run leaner for a while.
    It shouldn't move should it?

    I think everything is turned off or shut down that's possible.

    Any thoughts

    '95 LT1 if it'snot in my sig.

    Ta.
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  2. #2
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    A log and a bin should help alot.

  3. #3
    Fuel Injected! Terminal_Crazy's Avatar
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    Typically i wasn't logging then.
    I will when i find out where the oil is getting into the coolant from.


    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  4. #4
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    I don`t want to scare you but if there is no oil cooler in the radiator, the options are very limited.
    A cracked block is one option. In the heads there is no pressurised oil. If it was a gasket problem, it will be more likely a coolant in the oil problem.

    Did you see the actual afr fluctuating at the wideband.

  5. #5
    Fuel Injected! Terminal_Crazy's Avatar
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    It's a '95 Z28 LT1 with the KC4 Oil Cooler (Coolant runs around the Oil Filter type).

    The Oil is fine apart from it disappearing.
    I suspected the Edelbrock LT4 Inlet Manifold but have re machined the port faces.
    It is however leaking oil now from the rear wall since i went to synthetic after the rebuild.

    I've read a bunch of threads about the '95 KC4 leaking oil into the coolant.
    '93 and '94 seem to be better and by '96 it wasn't available.

    Not had chance this weekend to pull it off and check yet.

    Not sure yet also whether to delete it or to just install a full oil cooler.


    Thanks
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  6. #6
    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by kur4o View Post

    Did you see the actual afr fluctuating at the wideband.
    It always fluctuates at idle upto around half a point either side but I'm not to bothered about that.

    It was running for a good hour mainly sat around 12.5 but one time i looked it was sat at around 15:1.
    It never missed a beat, never changed tone or speed as far as i noticed.
    AFR was just up there.
    10 mins later it was back at around 12.5.

    I'll log it next time i run it just to check.
    I just thought it was a bit weird as everything is turned off that can be in tuner pro.

    Thanks
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  7. #7
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    Oil cooler is the main suspect. Extrenal leaks can`t get into coolant flow.

    You can bypass the oil cooler real easy.
    With a hose from radiator to pump and than check for oil leak from the disconnected pipe.

    At idle if you see more than +- 0.1, 0.2 afr change, the idle individual cylinder trims need tuning.
    They are really hard to tune though. Playing only with these trims you can get afr change from 11 to 15.

    You might have a exhaust leak or bad sensor.
    Check with the stock o2 sensor readings to confirm which side leans out.

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