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Thread: start up afr richer than commanded

  1. #1

    start up afr richer than commanded

    cammed 99 5.3 olsd, 226/232 113lsa 95# fic injectors with there data. my problem is only for a couple of minutes after start up (hot or cold) my afr is richer than commanded and i believe its causing me an idle issue because most of the time i have to stay on the throttle to keep it running untill it leans out to commanded afr. After idling for 3-4 minutes the afr climbs quickly (5-10 seconds) to commanded numbers. the only thing i can find is people saying the ve table is off, but it never switches to any other ve cell when it goes from rich to commanded. It likes to idle in the 800rpm and 60-65 kpa cells, and wile never leaving those cells, it goes from -11% for the first few minutes after start up to +-3% for the rest of the time the truck is running. turn the truck off and restart then it goes through the process again no mater if its hot or cold. olfa table is set to 1.0 after 50*
    I've spent a lot of time looking for a solution but I'm having no luck

    the below log doesn't show the transition from rich to lean because i ran out of time, but it shows it commanding 14.2 but running much richer.

    1red log.hpl
    1red v2 transient.hpt

  2. #2
    Tuning Addict 5FDP's Avatar
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    Is the IAT sensor working?

    Have you tried cutting the minimum fuel milligrams in half if you are having rich idle issue?
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  3. #3
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    i think it might be afterstart enrichment issue, (warmup enrichment/choke)

    edit: one way to solve it is to enable the closed loop and long term fuel trim at lower coolant temp like maybe at 93 instead of the stock which might be 149, keep in mind you need more fuel for cranking and warming up for the first 30 second at least
    Last edited by QTR FMS; 02-11-2019 at 04:42 AM.

  4. #4
    I haven't tried messing with the min fuel milligrams. I know in the tune it says stft are enabled but I normally leave ltft and stft off until I'm done with the ve table. I enabled stft just to see if it would help with my problem and it didnt.
    I'll have to double check the IAT sensor. But I will note, the initial adder vs iat table is zeroed out.

    As for after start, the decay delay, it has 32 revs in the operating temp range, and if my math is correct that should only last 2.66 seconds 720rpm/60=12 revolutions per second, 32/12=2.66 seconds. Even though that isn't adding in the decay steps I still dont think that's causing it to be rich for 3-4 minutes after startup. I Could be wrong though

  5. #5
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    Quote Originally Posted by LOWnEASY View Post
    I haven't tried messing with the min fuel milligrams. I know in the tune it says stft are enabled but I normally leave ltft and stft off until I'm done with the ve table. I enabled stft just to see if it would help with my problem and it didnt.
    I'll have to double check the IAT sensor. But I will note, the initial adder vs iat table is zeroed out.

    As for after start, the decay delay, it has 32 revs in the operating temp range, and if my math is correct that should only last 2.66 seconds 720rpm/60=12 revolutions per second, 32/12=2.66 seconds. Even though that isn't adding in the decay steps I still dont think that's causing it to be rich for 3-4 minutes after startup. I Could be wrong though
    check initial adder vs ect

    on gen 4 there is a table offset vs inj temp

    those are the only two tables i could think off , if your issue disappear in open loop i dont think its min fuel milligram

  6. #6
    Advanced Tuner uarperformance's Avatar
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    What about ECT adder after start enrichment

  7. #7
    back on to this problem, i zeroed out a good portion of the ect adder after start enrichment and still does it here is the newest tune and a good log of whats going on. (ignore the first 25 seconds of the log, as the wideband was still warming)
    redrocket 2019.hpt
    redrocket 2019 log.hpl

  8. #8
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    Quote Originally Posted by LOWnEASY View Post
    back on to this problem, i zeroed out a good portion of the ect adder after start enrichment and still does it here is the newest tune and a good log of whats going on. (ignore the first 25 seconds of the log, as the wideband was still warming)
    redrocket 2019.hpt
    redrocket 2019 log.hpl
    Im not looking at your tune as i dont have my laptop handy but is your PE table seting more rich in that area. I dont know 100,%but ive heard it will use what ever table has the more rich value.
    Again i dont know for sure but worth a look id say
    1997 30th SS. Torqhead 24x, TFS heads, 234/244 cam, 4l80e, Dana 60.

  9. #9
    No PE kicking in, this problem is at idle only. My pe enable is set at ~65% tps in the lower rpm ranges. When its having its problem, commanded afr is 14.2, wideband shows 10's-12's and then after a wile of idling commanded is still 14.2 and the wideband magically jumps to 3-7% of commanded. I dont belive it to be in the ve table, due to the fact it stays in the same rpm vs kpa cells during the transition from rich to stoich. Also i dont belive it to be a problem with the wideband because if I put it in gear wile its rich, the truck will stumble and stall 99% of the time. Put it in gear after it leans out to were it should be, then all is well.

  10. #10
    Any other advice?

  11. #11
    Advanced Tuner Lakegoat's Avatar
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    Under Fuel--General--your offset vs volts vs VAC table is set up like a dead head system instead of like a return like your IFR table.
    2005 GTO, TrickFlow 225, Magnuson 2300, 4L80, 4 link 8.8
    2013 Silverado 5.3, 6L80

  12. #12
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    After 1 minutes of running and 140 Degrees ECT your STFT goes from 0 to -32% Try reducing your VE table at idle and see what happens.

  13. #13
    Quote Originally Posted by Lakegoat View Post
    Under Fuel--General--your offset vs volts vs VAC table is set up like a dead head system instead of like a return like your IFR table.
    that is the data fic sent me, and there is only one set that matches my table.

  14. #14
    Quote Originally Posted by Davem3261 View Post
    After 1 minutes of running and 140 Degrees ECT your STFT goes from 0 to -32% Try reducing your VE table at idle and see what happens.
    good catch, now in the scan it looks like the o2 sensors start pulling fuel the same time it starts to lean out to stoich, now the question is why are stft's playing a part when there disabled in the tune?

  15. #15
    Turns out closed loop was still enabled. Thought I had it off but I didnt, so the stft were still active. shut it off and redone the ve table with the wideband and all is well. Thanks everyone.

  16. #16
    Senior Tuner cobaltssoverbooster's Avatar
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    Quote Originally Posted by LOWnEASY View Post
    that is the data fic sent me, and there is only one set that matches my table.
    these injector dealers assume you know enough to be able to modify the data to work with both systems.
    they give you constant pressure data because the boost referenced data only requires you to choose once column of data from the constant pressure field in order to populate the whole table.
    if you dont understand the different between calibrations for each then i suggest some more reading on injector calibrations.

    your ve table is going to be complete shit until you get the correct injector data so you need to fix this injector data issue first.
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  17. #17
    Tuner Boost's Avatar
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    Quote Originally Posted by 5FDP View Post
    Is the IAT sensor working?

    Have you tried cutting the minimum fuel milligrams in half if you are having rich idle issue?
    which table(s)
    GM dealer tech since 2005
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  18. #18
    Senior Tuner cobaltssoverbooster's Avatar
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    Transient section - min fuel mg
    It's just a single field parameter, no table

  19. #19
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    Quote Originally Posted by cobaltssoverbooster View Post
    Transient section - min fuel mg
    It's just a single field parameter, no table
    Kinda piggybscking this. I had 24lb injectors but now 36lb. Would i have to touch the min fuel mg away all?
    1997 30th SS. Torqhead 24x, TFS heads, 234/244 cam, 4l80e, Dana 60.

  20. #20
    Senior Tuner cobaltssoverbooster's Avatar
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    Only if your idle stays rich and doesn't change with ve adjustment. Some users just disable it instead of worrying about it. Up to you which way you want to go