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

[djxib]

(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

[gregs78cam]

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.

[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.

[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.

[PJG1173]

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.

[gregs78cam]

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.

[EagleMark]

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

[djxib]

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!

[djxib]

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!

[EagleMark]

:happy: