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

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.

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.

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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Originally Posted by EagleMark

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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I ran into the same issue and this corrected it for me.

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Originally Posted by RobertISaar

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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I agree, my LM-1 takes at least 20 seconds just to heat up and start displaying.

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

Quote:

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Originally Posted by EagleMark

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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Thanks - I'll give it a try!

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Originally Posted by PJG1173

I ran into the same issue and this corrected it for me.

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Removed some fuel from that table - now doesnt stumble when cold. Thanks all!

:happy: