Results 1 to 7 of 7

Thread: G8 really lean

  1. 07-18-2019 #1
    Srblacks13
    Srblacks13 is offline
    Tuner
    Join Date
    Jul 2019
    Posts
    182

    G8 really lean

    Long story short. G8 has mail order tune that is locked from previous owner. I'm getting a new unlocked pcm in the future to tune myself. I've been getting comfortable with the scanner and such, just playing around in the mean time. Anyways, logging some stuff tonight was scary. WOT commanded afr says .89. It's around there early but around 4800rpms it jumps to like .96 actual, even tho commanded is .89. Why the discrepancy? Not trying to melt pistons here. If not and easy answer, what should I look for and or log to check. Just trying to learn, thanks.
    Reply With Quote Reply With Quote
  2. 07-18-2019 #2
    5FDP
    5FDP is online now
    Tuning Addict 5FDP's Avatar
    Join Date
    May 2012
    Location
    Rogers, MN
    Posts
    13,559
    Assuming you are using a wideband in the exhaust that is pre-cat converter, that is surely an issue if the spread from commanded to actual is that far.

    It could be a calibration problem where the tune is not very well done and it needs work to bring the fueling in. Or it's a mechanical issue like fuel pressure is dropping off above that rpm and causing it to go lean.

    It would be worth it to see what fuel pressure is doing to make sure that is not part of the issue.
    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.
    Reply With Quote Reply With Quote
  3. 07-18-2019 #3
    Srblacks13
    Srblacks13 is offline
    Tuner
    Join Date
    Jul 2019
    Posts
    182
    I will check that. I'm very much a novice but in my short time reasearching I'm think the MAF or VE table are probably not correct which may be my issue. Unfortunately I cannot touch them since the pcm is locked. Looks like no more wot til it gets fixed
    Reply With Quote Reply With Quote
  4. 07-18-2019 #4
    Srblacks13
    Srblacks13 is offline
    Tuner
    Join Date
    Jul 2019
    Posts
    182
    Fuel pressure is 57.9 the entire time. Thanks.
    Reply With Quote Reply With Quote
  5. 07-18-2019 #5
    5FDP
    5FDP is online now
    Tuning Addict 5FDP's Avatar
    Join Date
    May 2012
    Location
    Rogers, MN
    Posts
    13,559
    The scanners fuel pressure channel is not always right. Often that channel does not work in many cars.

    I'd get a real gauge on it to make sure.
    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.
    Reply With Quote Reply With Quote
  6. 07-20-2019 #6
    Srblacks13
    Srblacks13 is offline
    Tuner
    Join Date
    Jul 2019
    Posts
    182
    Hooked up fuel pressure gauge. Solid at 60 psi the whole time. Went back to the logs and it actually happens as soon as I'm WOT. As soon as I see wot, it's .95 when commanded is .89. Must be the tune?
    Reply With Quote Reply With Quote
  7. 07-20-2019 #7
    sgod1100
    sgod1100 is offline
    Advanced Tuner
    Join Date
    Feb 2018
    Posts
    824
    Quote Originally Posted by Srblacks13 View Post
    Hooked up fuel pressure gauge. Solid at 60 psi the whole time. Went back to the logs and it actually happens as soon as I'm WOT. As soon as I see wot, it's .95 when commanded is .89. Must be the tune?
    post the log and tune...sounds like you just need to re-cal your maf
    Reply With Quote Reply With Quote
« Previous Thread | Next Thread »