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Thread: Open to close loop PE weirdness

  1. #1
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    Open to close loop PE weirdness

    Working thru tuning my Gen 3 turbo 2 bar build.

    Failed the MAF and setup OL
    Tuned the VE tables to a reasonable point up thru ~10psi (street tuning)
    Flipped the MAF back into play and left it in OL
    Touched up the MAF freq table to a reasonable point
    AND here comes the weirdness
    Put it back in CL took it out for a ride and when I hit boost it remains lean. This was not what was going on when I was in OL. This is my first tune and I was feeling pretty good and could not wait to set it to CL as I thought it might clean up the tune a bit more. Guessing I did something wrong, any tips on what to look for/change/??.

    I have enclosed my tune and log. You can see the condition occur in the first minute of the drive, you can also in the second minute if I roll into the boost soft it seems to be better.

    Any advice would be appreciated.

    ve9 maf3 cl2.hpl2005 Chevy Express 2500 - baseline Step4 ve maf cl.hpt

  2. #2
    Tuning Addict 5FDP's Avatar
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    I think your PE settings need to be changed to work better.

    Raise the MAP kpa from 55 to 90kpa, raise the boost kpa to 110kpa. Lower the enable torque to 50% and get rid of that 3,000rpm delay and .5s time delay. Change it 0 seconds and 1,500rpm. Increase the enrichment ramp in rate to 2.000 and lower the pedal enable some at lower rpm. I think it's easier to use the KPA settings to enable PE and BE than it is to wait for a rpm and pedal percentage.

    It should dip into PE much quicker and then down into BE when you want and stop a lean spike getting into boost.

    The VE could be a little smoother and that timing curve needs some help too. The LS can handle way more than 25-28 degrees of timing at part throttle. And it should be a smoother transition from top to bottom and left to right, no stair steps.
    Last edited by 5FDP; 08-04-2020 at 06:07 PM.
    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
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    Thanks for the PE tuning tips. I just added them and will check it out tomorrow and see if it helped the transition lag in PE/BE.

    I went with conservative timing and will get after that in a bit, need my balls to grow a bit larger first. I'm heading to a dyno in 4 weeks so the more I figure out now the better. I'll also smooth out VE once I get a little more experience too.


    Appreciate the help.

  4. #4
    Senior Tuner kingtal0n's Avatar
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    I would not try to use a maf in the forced induction application unless you are a maf sensor expert. The flow through a maf needs to be extremely linear, and a compressor wheel causes perturbations to the airflow which are anything but linear during throttle transitions and pressure changes. It can be done but you need to be a maf tuning expert to do it well. Anytime you lift from the throttle for example the air between the compressor and maf needs somewhere to go, the factory turbo cars which uses maf sensors all have a bypass valve which recirculates air from the compressor outlet back to the compressor inlet in order to prevent the compressor from surging and sending air back through the maf.

    and etc

  5. #5
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    Certainly not a MAF expert but I'm gonna run a MAF. This is a daily driver and I'm shooting for the whole experience. I get there are tons of guys running SD out there and super happy with it but I made the choice and I want to stick it out until I reach a reasonable failure point which ain't just yet.

    Made a pull with the new configs, still lagging but does not appear to be as bad. I do see it catch up on the graph in about a second but the gauge scares the crap out of me as I feel like it's lean for way longer than the graph is telling me so I always back off. I upped the enrichment ramp in to 2.5

    I also noticed I'm going rich after I hit about 170kpa so I pulled a little BE eq out, I know it's a hack but I'm learning so I figure I'd give it a try and see how the truck reacts. I also know I'm getting into areas of the VE I didn't hit previously so I'll need to tone it down a bit.

    I'll toss the tune/log up later tonight after a few runs and tweeks.

  6. #6
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    Guess I'm being stubborn and stupid at the same time.

    After a few runs I didn't get too far with eliminating the lean spike on PE/BE transition. I'm pretty sure that condition was not present when I was OL so I'm going to revert back to OL and maf fail to touch up a few more regions in the VE and see if that cleans up the lean spike. Then re-introduce the MAF while in OL and see how that impacts the lean spike.

    2 questions:
    Do I keep PE/BE enabled when I clean up the boost regions of the VE and just set the EQ's where I want them and tune VE accordingly? I assume yes but figured I'd ask.
    Also I tune out CL AND use the scanner to force OL by using the vehicle controls by disabling CL, disable LTFT Learn, and reset the LTFT, is that the right way to do this?

  7. #7
    Tuner in Training JoshuaGrooms83's Avatar
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    My understanding is yes, you want to still keep your PE/BE enabled when cleaning up boost. Its how im am tuning as well. If you are having an issue with certain regions, you may want to specifically target your lean/rich areas in the VE by RPM vs KPA vs AFR/LAMBDA. For me, I was having a massive rich condition in the middle of my VE due to an over conservative initial tune. In the 3400 rpm region in my tune, i would get 9.0 AFR and nearly stall trying to get anything over 40% throttle. After a while, i decide to specifically adjust those regions that i know by the scanner was over rich by adding -2 or -4% to that area, removing fuel in the process, and actually leaning out that area, where i actually was starting to see 10.5 afr finally. I was experimenting with this when i noticed the opposite was happening when i was doing the copy paste special method, and my idle region was getting too lean and my idle was getting rough to terrible. So i did this targeting the idle area in the VE and added about 4% and finally got my AFR to about 15-16 around that area. Now im actually seeing +/- 5% in a lot of ares where before it was 20 to 30% afr error in the cells before.

    As for open loop, yes you need to disable closed loop, disable/fail out maf and unplug it if you can, and disable LTFT, so you dont have anything else trying to adjust anything. Make sure to check out ChopperDocs VE tuning video or Goat Rope Garage VE tuning video to give you a really good reference of what to disable and and modify for speed density tuning.
    and you point is?