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Thread: Fuel dynamics mafless?

  1. #11
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    I have a customer with an E38, Maffless in a Nissan Patrol, it is used in competition and has a manualised Auto. The vehicle is perfect except for in tight trees where the throttle is opened and close repeatedly rapidly, under these circumstances it will lean out to the state of a missfire, I played with the dynamics for a day with no result, I suggested the customer refit the MAF as it was my feeling that the SD was the issue, I'm glad to see that seems correct even if there is no SD optimum fix.


    Joel

  2. #12
    Lifetime Member mr.prick's Avatar
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    I wonder if re-enabling the MAF would cure this for the LS1.
    The dynamics stuff didn't help at all and I wondered if it could be injection timing or
    because the exhaust flow across the WBO2 slowed down too fast for the sensor.
    It only happens when TPS% decreases quickly.
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  3. #13
    Lifetime Member Tre-Cool's Avatar
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    as promised, 3 logs from the night.

    the attached tune isnt the exact tune we ran, but it will give u an idea on the dynamics that we were running.

    stock ls3 with springs and 71c thermostat and twin turbo 2871r.
    Attached Files Attached Files

  4. #14
    Joe (Moderator) joecar's Avatar
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    Simon, nice write up of your observations...

    What would happen in CL-SD...? Would you get the same MAF-less limitation on dynamics, but with return to stoich aided by STFT's...?

  5. #15
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    Simon, this is some cool stuff... I've seen all this before, but I usually have attributed the AFR spikes on shifts to a fuel system. I still believe it's partially correct, as I've seen improvements after the fuel systems were upgraded, especially to return systems. Have you noticed anything similar?

  6. #16
    Lifetime Member swingtan's Avatar
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    L31Sleeper: There are no calculations in the VVE that use MAF airflow. The VVE is a theoretical map of predicted airflow, so there is no need for any actual air flow figures to calculate it.

    4wheelin: Exactly the point I was mentioning. Any time you have repeated and rapid on/off throttle events when in SD, you get the lean out. However, for a full race vehicle, I'd just up the stomp factor a bit to mask the effect as well as richen the VVE during off throttle events. If fuel consumption doesn't play into the competition, it shouldn't worry too much.

    mr.prick: If you are referring to the "rich on throttle close" issue, there is a table in the E38 B2011 - Wall Wetting Asymmetry Factor. This can be used to balance the throttle open vs throttle close events. It doesn't appear that the LS1 has this table, or it may not yet be defined. Looking at the log though, I don't think it would worry things too much.

    joecar: Yes, I think you are right. CL-SD would have the dynamic control issue, but the O2's would help to control the return to CL. This may help to stop any lean out on throttle close but you still have to compromise the settings for throttle open ( entering PE mode ).

    redhardsupra: I've not altered the fuel system in my car so can't comment on that. What I have noticed is that
    • The bigger MAF is no hindrance to power
    • If the VVE is set correctly and the tune is good, running the MAF feels better in a daily driver than running full SD ( due to the dynamics I think )
    • Running CL helps greatly with the fueling and lean cruise does not seem to work quite as well in the Gen IV.


    What I would like to try though, it to get the O2 switch point settings to work in the E38 and try some adjustable CL fueling. I think that that would have some very interesting results.

    Simon.

  7. #17
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    swingtan, when you say 'OL-MAF' and 'CL-MAF' is that full maf or maf + tuned VVE

  8. #18
    Lifetime Member swingtan's Avatar
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    I guess that will depend on how the tune is set up......

    If you alter B2804 / B2805 to switch over to MAF only air flow very early, then the VVE will have no effect on fueling. In this case there would be little need to adjust the VVE as it's not referenced. This would be an option for CL-MAF as long as you trust that the MAF will not drift too far. The O2's will compensate for minor differences in air flow when cruising, and the PE mode airflow can be set up and left.

    If you leave B2805 and B2805 so that the VVE is still referenced, then you will need to optimise the VVE for the area where is is used. This is because under the "High Speed Air Mode", the VVE is used as a "rationality test" for the MAF to ensure it's reading correctly. If the VVE is off, then the ECM will alter the MAF reading, skewing it toward the VVE setting. This is probably the major reason why SD tunes appear to be better, as most "MAF" tunes do not address any VE or VVE errors. As many have mentioned, to do a "proper" MAF tune, you still need to dial in the VE / VVE where it is still referenced.

    I've tried both and found that switching to MAF only air flow readings works very well. I have B2804 set to 1000 RPM ATM.

    Simon.

  9. #19
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    Is it safe to assume that you're failing the MAF in the stock OS to get SD functionality? Does this same limitation exist in COS?

  10. #20
    Lifetime Member 5.7ute's Avatar
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    Quote Originally Posted by LinearX View Post
    Is it safe to assume that you're failing the MAF in the stock OS to get SD functionality? Does this same limitation exist in COS?
    It would.
    From what I have researched the "pump shot" which would prevent this condition is disabled when the maf is failed.
    BTW a great write up Simon.
    The Tremor at AIR

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