MawneeC5

iTrader: (12)

I've been getting the tune dialed in on my Turboed Z06 and about 2 days ago it seemed like I had the lower portion of the VE table looking good(error within a couple points). My AFRs were sticking near 14.7 idle/cruising and PE areas were still fat, but working as intended. Car was running great, idling perfect. I was just starting to tune pushing into boost so I could trim the VE table down up there.

For most of my tuning its been cool and dry down here in florida, 50s at night during tuning. Now the last couple days driving to and from work its been 80s, raining and humid.

Suddenly my AFRs are roughly 1 point leaner across the board. Cruising I'm getting 15.5-16.5 and can definetly feel it buck as it leans out. If I push the throttle to roll it into PE its going to 12.9-13.5 whereas before it was mid 12s. I dont detect any missing or leaks. I checked plug wires and connections. The car is running fine but I can tell it is lean. It smells hot, though coolant temps are fine. I can smell my header wrap again and that was pretty much done burning in a week ago. I even tried flashing back a couple of days in my tunes which should be a touch richer, and it was pretty lean.

Could the weather really have that drastic of an effect or am I missing something stupid?

Car is 2003 Z06
228R
TC76 custom top mount(similar to hinson)
60lb siemens
SD 2 bar tune, no maf, O2s disabled(no fuel trims)

MawneeC5

iTrader: (12)

I just compared my IATs to earlier that day before the rain got here. They seem about the same. But look how close my tune is on this log.

DMM

I have had the same experience to a degree, although I kept the O2 sensors and still have LTFT's enabled. One day I'll be +/- 2 LTFT's and two days later I am +/- 8. I have been told this happens to a varying degree, granted a full point leaner seems excessive. I have been told by a few people this is why a scaled MAF is the way to go.

ACCLR8N

If you have no fuel trims, that could do it. I see variations in my fuel pressure depending on ambient temps. Also system voltage. Both will throw off how much fuel is actually squirting into the cylinders. The voltage is compensated for, but might not be accurate enough. I can't imagine running through those kinds of weather changes without O2 feedback.

MawneeC5

iTrader: (12)

I think I have traced this back to the voltage offsets table. I was able to reproduce this issue last night after taking a few people for a quick ride in the car. I would take them for a few minute ride, park the car and turn it off. After doing so the car went lean again. I noticed that my battery volts were down to just over 13v where normally I am just above 14v.

This would also explain why the other night it kept going leaner. Because I kept turning off the car and reflashing the battery got lower and lower.