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90 CRX Si
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Discussion Starter #1 (Edited)
So i went to the track the other day and made some DL'ing passes (2 i recorded anyway). I noticed that theres a big spike down to around 10:1 AFR when I hit 3rd gear, then pulls back to around 12.5:1 within 2 seconds, so I know its hurting my time. I did a 2nd gear pull yesterday, from ~3k to rev limit (7800), and noticed no such drop. The only thing I'm thinking is that my VTEC engagement is at 5500, and disengagement is ~4800, and it may be that my rpms fall to right around 5K, lower than engagement, but not low enough to go back to the low cam maps.

Oh, and also, my car seems to be richer in 3rd gear than in 2nd, where it stays right around 13:1 in 2nd, its ~12,4:1 in 3rd. I got to figure something out, i lost .6" and 3mph the other day versus my old time. Partly b/c it was 100% humidity and track prep sucked, but my tune's different too.
 

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Have you recorded enough to know exactly where in the map this spike happens?
Try setting your vtec low (say around 3k rpm) then DL the afr sweep from there onwards.
Then reset your vtec high (to around 7k rpm) then DL the low cam sweep.

Chances are you might see where the spike is coming from (lowcam or hicam) since your suspicion on vtec transition point seems kinda valid.
 

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90 CRX Si
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Discussion Starter #5
Got to DL at couple of 2nd gear pulls to find out the where the spike is, and on the High Cam maps (vtec was set to 3500), around 5K it spiked down to around 10:1 the first time. I pulled some fuel around there, and only seemed to spike to 12:1, better, but still my fuel is not high there, its relatively lower than above 6K.
 

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Maybe you could pull a little more there (3.5-5k) so that transition can be smoother once you switch back to your usual 5.5k vtec.
Who knows, somehow the ecu might be interpolating by a fraction of a sec from the high cam side just prior to vtec switchover so the higher fuel values pull down afr around <=> vtec region..
I feel 12 is still rich and could still be trimmed a bit.
 

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1990 civic 4 door LX
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You are running into an issue on the second turbo Vtec car I ever tuned... and understanding the interpolation is awesome at full throttle. Partial throttle whil slightly climbing vac. pull makes it hard to interpolate the differences.
 

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So i went to the track the other day and made some DL'ing passes (2 i recorded anyway). I noticed that theres a big spike down to around 10:1 AFR when I hit 3rd gear, then pulls back to around 12.5:1 within 2 seconds, so I know its hurting my time. I did a 2nd gear pull yesterday, from ~3k to rev limit (7800), and noticed no such drop. The only thing I'm thinking is that my VTEC engagement is at 5500, and disengagement is ~4800, and it may be that my rpms fall to right around 5K, lower than engagement, but not low enough to go back to the low cam maps.

Oh, and also, my car seems to be richer in 3rd gear than in 2nd, where it stays right around 13:1 in 2nd, its ~12,4:1 in 3rd. I got to figure something out, i lost .6" and 3mph the other day versus my old time. Partly b/c it was 100% humidity and track prep sucked, but my tune's different too.
Your car is richer in third due to the increased load. In really low gears, especailly if you have any amount of wheelspin, AFRs are leaner.

Is this car NA? Do you have datalogs you can share?
 
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