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Thread: Startup Enrichment - DA2/DA3 (1992/93 Corvette)

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    Startup Enrichment - DA2/DA3 (1992/93 Corvette)

    (1992 Vette, LT1, 236/246 cam, LT4 heads/intake, 9:1 CR and V7-YSi, open-loop tune)

    I am trying to improve initial startup performance on this car - it cranks and fires just fine but after a few seconds it struggles to maintain idle and threatens to quit. AFR on my wideband shows 12-13:1 during this time so I believe it's too lean. On a 80-degree day the car will usually idle like a pig for about 30-45 seconds and then settle down, after which it runs great.

    Question is - how soon does the startup enrichment table (startup enrichment vs. coolant temp) time out, will it cover this initial 30 - 45 second window? ..or should I fix it in the open loop tables (Open loop enrichment vs coolant temp).

    Thanks!
    Andy

  2. #2
    Fuel Injected! gregs78cam's Avatar
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    Actually 12-13:1 is rich and for a cold engine at startup is close to normal. It may be that the idle speed needs to be increased to go along with the start up enrichment.
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    RIP EagleMark's Avatar
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    With that cam the vacuum would be lower and already be enriched, so 12-13 AFR may be low at cold... so being OL I think Id give "Open Loop %Change to Fuel/Air Ratio Vs. Cool. Temp. " a shot.

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    widebands CANNOT be used to accurately determine AFR so soon after startup... reason being that there is a lot of raw fuel that is still getting sent out of the combustion chamber that may or may not combust in the exhaust.
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    Fuel Injected! PJG1173's Avatar
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    Quote Originally Posted by EagleMark View Post
    With that cam the vacuum would be lower and already be enriched, so 12-13 AFR may be low at cold... so being OL I think Id give "Open Loop %Change to Fuel/Air Ratio Vs. Cool. Temp. " a shot.
    I ran into the same issue and this corrected it for me.
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    Fuel Injected! gregs78cam's Avatar
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    Quote Originally Posted by RobertISaar View Post
    widebands CANNOT be used to accurately determine AFR so soon after startup... reason being that there is a lot of raw fuel that is still getting sent out of the combustion chamber that may or may not combust in the exhaust.
    I agree, my LM-1 takes at least 20 seconds just to heat up and start displaying.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

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    RIP EagleMark's Avatar
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    Well there's 2 reasons a WB is no good for start up...

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    Quote Originally Posted by EagleMark View Post
    With that cam the vacuum would be lower and already be enriched, so 12-13 AFR may be low at cold... so being OL I think Id give "Open Loop %Change to Fuel/Air Ratio Vs. Cool. Temp. " a shot.
    Thanks - I'll give it a try!

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    Quote Originally Posted by PJG1173 View Post
    I ran into the same issue and this corrected it for me.
    Removed some fuel from that table - now doesnt stumble when cold. Thanks all!

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    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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