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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
    Tuner in Training
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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; 5 Days Ago at 05:42 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
    Tuner in Training
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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