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Thread: DFCO airflow?

  1. #1
    Advanced Tuner
    Join Date
    Oct 2004
    Location
    Huntingtown, MD
    Posts
    200

    DFCO airflow?

    On my 2001 Silverado 1500HD with 6.0L gas engine, I just rebuilt the heads and installed a mild aftermarket cam for good measure. Anyway, while redialing in the tune, I took my family on vacation (in the truck) and left DFCO disabled for roughly 3000 miles. During that time the truck barely used 1/8 of a quart of oil, which is great for one with 273k miles. Anyway, I got home, dialed in the tune and enabled DFCO to find that oil consumption picked up, so I'm thinking the extra vacuum under DFCO is sucking oil in the PCV value.

    I was poking around in HPT and under idle->airflow there are a few parameters related to "DFCO airflow". "Idle DFCO Entry hold time" says time delay before entering DFCO airflow. Is there a DFCO airflow table that we can't see? Does the PCM target that table under DFCO? Anyone played with "Idle DFCO Entry hold time"? I'm curious if I crank that value up if the truck will still go into DFCO, but maybe not close the IAC or whatever it's doing.

    I plan to do a bunch of logging this week, but would love to learn if someone has already played. Thanks again.
    Phil K.
    02 Camaro SS 5.7L LS1
    01 Silverado 1500HD 6.0L LQ4 4L80E 78/75 turbo with Flex Fuel

  2. #2
    Advanced Tuner
    Join Date
    Oct 2004
    Location
    Huntingtown, MD
    Posts
    200
    Well I tried three things 1) DFCO on with stock DFCO airflow rates, 2) DFCO off, and 3) DFCO on with zero DFCO airflow enter rate. Logging all three and looking at MAP and IAC values, there must be some DFCO airflow table that we can't see, because the IAC was closed a lot farther in 1 than 3. With the zero airflow rates, the IAC counts are basically the same under deceleration than with DFCO disabled.

    The engine braking effect under 3 is reduced, from the reduction in manifold vacuum. Honestly, I like the reduced engine braking so that I can stay in DFCO longer. From the IAC staying more open, I had to significantly change my MAP exit values. Overall, having DFCO on with zero DFCO airflow enter rate has giving me what I want, now I have to drive around and monitor MPG's.

    My last comment is when playing with the DFCO airflow timings (delay and enter rate), the delay says it's in seconds. However, when I first tried just increasing that value to 30 seconds and leaving the enter rate stock, I could still see the IAC closing much faster than 30 seconds (more like a 3 second delay). It's not a big deal because I just zeroed the rate, which accomplishes what I want. However I thought I would mention that the DFCO airflow delay timing units don't seem correct.
    Phil K.
    02 Camaro SS 5.7L LS1
    01 Silverado 1500HD 6.0L LQ4 4L80E 78/75 turbo with Flex Fuel

  3. #3
    Potential Tuner
    Join Date
    May 2017
    Posts
    5
    I know this is an old thread, but I agee that there must be some sort of parameter we don't have that controls the airflow during DFCO. It would be nice to be able to change that. My DFCO airflow settings were all zero stock on my 05 silverado.