AFRs 20% lean for 5 - 10 min on startup
09-29-2005, 12:58 PM
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AFRs 20% lean for 5 - 10 min on startup I am tuning my '98 C5. AFR heads, G5X3, LS6 intake, long tubes, 30 lbs SVO injectors. Recently hooked up LC-1 for some SD tuning.
All is going well except the wideband is reading extremely lean AFRs for the first 5 - 10 mins. after a restart. Happens when car is hot or cold. Happens with my SD tune and with my full MAF tune.
I wasn't too concerned about this - i've learned to let the AFRs stablize and richen up before beginning any serious logging. However, I start working on my idle trims. After making adjustments, the cats began glowing as the trims worked down close to 0. I have rear O2 sims so no COT richening.
I've put the idle values back to keep it artifically rich for the time being. After talking to some other folks, I am learning this 5+ mins of extremely lean AFR is not normal.
Wracking my very small brain here.
Any ideas?
All is going well except the wideband is reading extremely lean AFRs for the first 5 - 10 mins. after a restart. Happens when car is hot or cold. Happens with my SD tune and with my full MAF tune.
I wasn't too concerned about this - i've learned to let the AFRs stablize and richen up before beginning any serious logging. However, I start working on my idle trims. After making adjustments, the cats began glowing as the trims worked down close to 0. I have rear O2 sims so no COT richening.
I've put the idle values back to keep it artifically rich for the time being. After talking to some other folks, I am learning this 5+ mins of extremely lean AFR is not normal.
Wracking my very small brain here.
Any ideas? 
09-30-2005, 01:14 AM
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99 C5 here. Mine does the same thing. I like the air system suggestion. Seems to make sense because it is not a gradual transition, it is somewhat abrupt. I will try to confirm this weekend.
09-30-2005, 10:31 AM
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Originally Posted by SideStep
RESOLVED!!!
Do not get overly aggresive in the base spark closed throttle tables. The cats don't like too much initial timing.
Also, it's good idea not to take someone else's table and do a heavy handed paste without reviewing things first.
Thanks for the input and assistance!!