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Thread: Idle AFR changing whilst Idling

  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.

  8. #8
    Fuel Injected! Terminal_Crazy's Avatar
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    I bypassed the cooler and ran the car.
    Oil started weeping out of the cooler pipe so i’ve Deleted it for now.
    The coolant recovery tank was also full of oil so it’s all been flushed out and cleaned.

    I’ll log the idle next time I play with it and get back.

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

  9. #9
    Fuel Injected! Terminal_Crazy's Avatar
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    Ran and logged the car today.

    Still running OLSD with flat AFR at 13:0.
    This log was just from cold startup & idle.
    2017_11_19-001.jpg
    2017_11_19-002.jpg

    O2's and plugs only have about 1k miles on them.

    In my previous log it showed similar results so in this I've increased the rhs cyl trims from 1.03 to 1.047.
    However this could be a wrong assumption on the rhs being lean.

    Measured exhaust temps 1" out on header
    FRONT
    165 163
    196 182
    183 169
    171 153

    EEHAck idle cylinder test
    cyl 1 28.2
    cyl 2 29.2
    cyl 3 27.9
    cyl 4 28.3
    cyl 5 28.2
    cyl 6 28.5
    cyl 7 29.6
    cyl 8 28.5

    Where next?
    Do i change plugs & O2 Sensors anyway as I'll have to remove them to check them anyway.

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

  10. #10
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    There might be some mechanical problem with right side. Cylinder misfiring or injector problem. Number 8 seems a little cold.
    Exhaust leak is also a possibility.

    Right side o2 goes flat and it also shows lean at same time on the wideband. So sensors should be ok.

  11. #11
    Fuel Injected! Terminal_Crazy's Avatar
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    I'm running out of ideas.
    Since rebuilding the motor I've checked everything multiple times.
    Pretty much everything is new except the pan and block.
    It's had split BLM's and had O2 differences.
    It's on it's 3rd set of injectors, 2nd set of NEW o2's

    I'm pretty certain the manifold (Edlebrock LT4 performer was) passing air underneath, the ports were wet when i emoved it.
    I've remachined it (bought a mill to do it) but not 100% convinced it's sealing the ports.
    If I end up removing it I'll have to re mill it and cut down some of the larger sealing areas.

    Exhaust leak is pretty unlikely, been over them many times, including the egr ports. ** Might just recheck the M22? plugs i fitted to the headers 9 years ago ***

    Cylinder misfire possibly but Steveo's EEHack disdn't highlight any issue with the cylinder test which was straight after the uploaded datalog where the RHS has pretty much flatlined.

    Odd how both sides drop around 300Secs and by 550 the RHS has recovered until 1200 secs when it starts to drop again.

    Weird !

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

  12. #12
    Fuel Injected! spfautsch's Avatar
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    One of kur4o suggestions was cylinder misfiring - wouldn't that generally cause a rich condition when running open loop?

    Are the m22 plugs you mention blocking off the AIR ports?

    Can you reproduce this symptom from cold startup?

    As you say this really is odd. I would think the lazy right narrowband reading could be indicative of an open heater circuit, but that doesn't explain the very distinct event around the 5 minute point in the graph that's clearly effecting the wideband as well.
    Last edited by spfautsch; 3 Weeks Ago at 02:49 AM.
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

  13. #13
    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by spfautsch View Post
    One of kur4o suggestions was cylinder misfiring - wouldn't that generally cause a rich condition when running open loop?

    Are the m22 plugs you mention blocking off the AIR ports?

    Can you reproduce this symptom from cold startup?

    As you say this really is odd. I would think the lazy right narrowband reading could be indicative of an open heater circuit, but that doesn't explain the very distinct event around the 5 minute point in the graph that's clearly effecting the wideband as well.
    Hi
    I think Misfire causes it to run lean as it measures the O2 content which has just jumped by 25-30%
    The M22's block off the AIR ports (1 per header) ...seem OK

    Reproducible with tonights log. The dip is there around 4-5 mins but isn't important as motor is only 50c then.

    Not as odd as tonights log.
    Does anyone want to have a laugh at this.

    Checked the M22 bolts in the headers. Seemed OK, no blowing.

    Previous: LOG a30 idle: RHS O2 sensor dropping LEAN & WB AFR rising to 16-8...

    LOG a30-2_idle
    Ran another idle test & used EEHack to play with the timing & AFR
    Graphed with EEHack
    Top graph AFR Target & Wideband O2 AC Pressure
    Bottom graph Left O2 Oxy Sensor mV & Right O2 Oxy Sensor mV



    Warmed up car on same bin till 90c | same as previous log
    Both drop around 4-5 mins | No idea but not important as car is on 50c here
    |
    log @ 9k dropped 5 degrees timing 32 ish | no observed change
    |
    9k8 AFR 14.7:1 | Both O2's drop off the scale
    10k2 14.0:1 | O2's pick up slightly
    10k6 13.0:1 | as normal
    11k 12.5:1 | better
    11k5 12 :1 |
    |
    12k4 timing +5 degrees (37) | no real change
    12k7 timing -5 degrees (32) | no real change
    13.1 AFR 13.1:1 | both O2's bouncing about
    |
    15k1 cut cylinder 1 - flat lined BOTH o2's ??? |
    15k2 cut cylinder 2 - flat lined BOTH o2's ??? |
    15k3 cut cylinder 3 - flat lined BOTH o2's ??? |
    15k4 cut cylinder 4 - flat lined BOTH o2's ??? |
    15k5 cut cylinder 5 - flat lined BOTH o2's ??? |
    15k6 cut cylinder 6 - flat lined BOTH o2's ??? |
    15k7 cut cylinder 7 - flat lined BOTH o2's ??? |
    15k8 cut cylinder 8 - flat lined BOTH o2's ??? |
    |
    16k5 Settling back |
    |
    16k6 AFR 9.1:1 | stable
    AFR 10 :1 | stable
    17k5 AFR 11 :1 | stable
    18k AFR 12 :1 | slightly eratic
    18k5 AFR 13 :1 | back to very eratic


    Weird results, but I don't know what it tells me other than it likes fuel.

    The only thing i'm aware of in the bin that's not correct is the Injector Flow rate I've lowered to 37 to scale the VE tables down.
    Injectors are Now 42lb Bosch III Blue Demon (EV1 plug EV6 style) from FIC
    Also had previously
    30# VENOM Rated at 30 lbs/hr @ 43.5 psi
    and (Bosch III FIC 312.6 / 10.2 = 30.64)

    Why would cutting 1 cylinder flatline both O2 sensors or is 100 data logs not enough to recover ?

    The two EEHack data files are in the Zip


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

  14. #14
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    I need to see some cruising logs at constant speed, load to confirm some ideas.

  15. #15
    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by kur4o View Post
    I need to see some cruising logs at constant speed, load to confirm some ideas.
    Thanks, I’ll post up the last run that I did tomorrow.
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

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