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Thread: Idle too lean when warmed hot? also help logging boost.

  1. #1
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    Idle too lean when warmed hot? also help logging boost.

    1998 ws6
    5.3 engine
    t70 turbo
    60# injectors
    320lph pump

    2bar map OS with 2 bar map(of course)


    the car runs pretty good and smooth at the moment but ive noticed that after its been running for a while(hot) the idle starts to lean out in the 16.+ range.

    what could be causing this lean out at hot temp?



    also how are you guys logging boost with 98?

    from my search it says that i simply keep the map sae.
    Ive tried making custom pid with the
    [PID.11.IMP]-14.5

    but it shows 22ish psi at idle.


    ive attached a log that shows the idle leaning out.
    Attached Files Attached Files

  2. #2
    wasn't that a pretty common problem on the f-body's? Has to do with the placement of the IAT above the radiator in the intake tube. The real fix would be with the cylinder charge temperature bias table but it seems no one has figured out a good way to adjust that table. The common fix is move the IAT sensor out of the engine bay. Also you have a '98 wasn't that a bastard year for f-body pcm's? Doesn't everyone suggest a '99+?

  3. #3
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    Quote Originally Posted by joshmith View Post
    wasn't that a pretty common problem on the f-body's? Has to do with the placement of the IAT above the radiator in the intake tube. The real fix would be with the cylinder charge temperature bias table but it seems no one has figured out a good way to adjust that table. The common fix is move the IAT sensor out of the engine bay. Also you have a '98 wasn't that a bastard year for f-body pcm's? Doesn't everyone suggest a '99+?
    I wasnt aware that the IAT had to be placed outside of the engine bay when doing turbo conversion. all pics ive seen have them planted where oem distance is at. I thought the IAT had to be as close to the TB as possible for the best accurate reading?
    where did you find that discussion of moving the IAT?

    yes but ive seen plenty run the 98 pcm and had no issues. people that took the time to tune them says they are more than capable. with a mild setup like mine i dont think a 99+ is needed
    i mean other than that lean out issue im having i say the pcm is plenty capable for what i need.

  4. #4
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    I think the issue is along the lines of heatsoak. I've been dealing with this on my build. Both my fuel lines and my IAT sensor were heatsoaking and causing leanout, mostly due to underhood temps. Here's what has helped alot: Cylinder charge Bias set to 1 across the board. This uses 50% iat and 50% ect for heat compensation, so a more stable change with less response to IAT fluctuation. The other thing that has helped is keeping fuel as cool as possible. Don't run 2nd fuel pump all the time , make sure lines are not too close to exhaust , use lots of heat shielding.
    2001 Z06 : 856/830 : Built LQ9 403ci : D1SC 17psi : Self-built , self-tuned.

  5. #5
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    Quote Originally Posted by nkautz View Post
    I think the issue is along the lines of heatsoak. I've been dealing with this on my build. Both my fuel lines and my IAT sensor were heatsoaking and causing leanout, mostly due to underhood temps. Here's what has helped alot: Cylinder charge Bias set to 1 across the board. This uses 50% iat and 50% ect for heat compensation, so a more stable change with less response to IAT fluctuation. The other thing that has helped is keeping fuel as cool as possible. Don't run 2nd fuel pump all the time , make sure lines are not too close to exhaust , use lots of heat shielding.
    underhood temp doesnt feel too hot thought. but my ect does read 230*. so perhaps thats whats causing my heat soak. all exhaust piping are wrapped untill halfway in the car(so all engine up to the driveshaft.

    I only have 1 pump. aem 320lph. and stock fuel lines.

    I guess i will attempt to move the iat out of the engine bay.
    ^^ will this affect my tune much?

    edit where is the cylinder bias located?

  6. #6
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    If you are boosted , you want your iat in your intake piping before the throttle body or in the intake manifold. This is so you get an accurate reading of your boosted air temp. Very important. ECT is high , I would consider 230 overheating. If I see 200 on my car , I start getting worried. Something might be wrong with your cooling system or you might need a lower temp thermostat. Cylinder charge bias is under engine -> airflow -> general. If you change the bias you will need to retune your ve.
    2001 Z06 : 856/830 : Built LQ9 403ci : D1SC 17psi : Self-built , self-tuned.

  7. #7
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    yes the car is boosted.

    interesting I always thought these car ran in the 210 range. atleast thats what the gauges always run at before I even turbo the car. it still run at around 210 but hptuners log shows 230.
    the fan doesnt even kick in until around that range

    I see where its located. thank you.

    edit I just looked at the stock temp fan is turned on and hptuner shows fan 1 on at 226 fan two at 234...

    I guess ill lower that and see if that helps
    Last edited by tuned2boost; 04-08-2015 at 10:34 AM.