Results 1 to 5 of 5

Thread: KPA vs Absolute Manifold Pressure reading discrepency

  1. #1
    Tuner in Training
    Join Date
    Feb 2020
    Posts
    14

    KPA vs Absolute Manifold Pressure reading discrepency

    Hello,

    Have an 04 Silverado 2500
    LQ4
    SS2
    Deka 80's
    3 Bar
    GT45

    My boost gauge has always read more than my MAP, (but Sunpro Ebay special doesn't exactly mean accurate). I had the EFI source MAP, switched to the Camaro MAP. Both of these ended up reading about the same under boost.

    The turbo seems to either be pumping hot air, my IAT's rise insanely fast, despite the sizable intercooler, or it's actually pushing more boost than the MAP is telling me.

    Either my MAP is reading incorrectly, and I actually am humping about 15-17lbs through, or this turbo is out of it's efficiency range at like 7-8lbs as per the falling boost curve.

    I am also curious as to why my absolute manifold pressure is telling me over 30lb (minus 14.5), but my KPA is telling me 7-10. This is the standard 312.50/11.25 offset unit.

    Anyone shed some insight? A few pulls attached as well as my current tune.



    100 pull.hplbc up pull.hpl1-2.hplfans screwing around.hpt

  2. #2
    Tuning Addict 5FDP's Avatar
    Join Date
    May 2012
    Location
    Rogers, MN
    Posts
    13,533
    You can't log more than 1 MAP sensor channel. You have the SAE map sensor channel for the 1 bar sensor and you also are logging the 3 bar sensor channel.

    The 1 bar MAP channel must be removed. The log shows the MAP maxing out at 105kpa and it could skew other readings in the scanner when logging both.

    The tune needs some help. You really should turn off the long term fuel trims, those are dumping in a ton of extra fuel and it's carrying over into PE/BE.

    I'd put this in open loop only while you fix the VE with your wideband.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Tuner in Training
    Join Date
    Feb 2020
    Posts
    14
    Quote Originally Posted by 5FDP View Post
    You can't log more than 1 MAP sensor channel. You have the SAE map sensor channel for the 1 bar sensor and you also are logging the 3 bar sensor channel.

    The 1 bar MAP channel must be removed. The log shows the MAP maxing out at 105kpa and it could skew other readings in the scanner when logging both.

    The tune needs some help. You really should turn off the long term fuel trims, those are dumping in a ton of extra fuel and it's carrying over into PE/BE.

    I'd put this in open loop only while you fix the VE with your wideband.
    Thanks. I know it's pig rich, but I thought because it's in open loop under full throttle, it wouldn't matter.

    About half way down you see the 3 bar absolute manifold pressure? I will disable the 1 bar and see if anything changes. I am perplexed as to what boost I actually am seeing.

  4. #4
    Advanced Tuner
    Join Date
    Feb 2014
    Location
    Sydney
    Posts
    295
    Your closed loop fueling is running too lean, the long term fuel trims are adding at WOT this is why it is "pig rich"
    Tune with actual data not simulated data!.....Applied Road/track Tuning

  5. #5
    Tuner in Training
    Join Date
    Jul 2019
    Posts
    12
    My snow kit is what i use for my in dash boost reading and it always shows a few psi higher than the scanner map shows. I think it's two things together that skew what you see, but the pcm is actually getting the correct info. It's just that when you look at the scanner I will increase boost faster than the pid can update the data in the scanner so you see it lagging behind some, it just skips from 105kpa to 165kpa to 220kpa and doesn't flash any other readings in between sometimes. The boost gauge updates in real time to its display much better. Also, the 3 bar os resolution is crap and scales in 20kpa increments past 100kpa which is 3 psi. So you have to go past the 3psi, 6psi, 9psi, 12psi, etc...increments to get into a new VE cell. Same fuel cell for 9psi and 11psi. It only sees 1/3 of what your gauge sees.