it's funny my car runs fine during the day. but at night it runs lean. why is this and how can i fix it? is it a temperature thing? it's been like this for the past week.

 

cold air is dense. dense air = more power. more power requires more fuel.

 

to help you guys out have a better picture, i'm running a drag 3 kit on a b16a only boosting 5lbs. fuel management is a MSD fuel pump and a 12:1 fmu. car was running fine for three months now nite and day it was all good. just this past week it runs lean at night. i live in HI and the temp change isn't that big from day to nite, maybe 79 in the day and 65 at nite. could it be my spark plugs or sumptin cuz i gots oil in the spark plug holes wen i pull my wires. thanx for any help.

 

the oil in your spark plug holes is from bad valve cover seals that enclose those holes from the rest of under the valve cover...
I had the same thing going on with the oil and the lean-out during the nights. All it takes is 15 degrees difference to throw things off.
why do you htink people spend $300 on a cold air intake? cus it draws in colder air making more power(2 or 3hp)(and its also why most retailers sell the fpr and computer chips along with kits to compensate for the colder air temps).
Ya this was way to long. Do a search reguarding "More boost when cold?"
Or something...there was a huge speel about that...

 

How do you know it's ruing lean? You cant trust aair/fuel ratio gauge thats hooked up to your stock o2 sensor.
Detonation?

 

if the stock o2 sensor is showing lean, then you're leaning out to 14.7:1 in boost, which is something i wouldnt do even at a modest 5psi.

 

of course, you could have a poorly powered/grounded gauge, and its the addition of the headlights as an electrical load which makes the gauge think you are getting lean.

 

Wouldn't that be stoich? lean for a turbo car though. I just stated that the air/fuel ratio gauge hooked up to a stock o2 is not that accurate....hell if it was mine would have done some nice dancing when i was runing richer then 10:1 but insted it read bairly rich

 

so if the cold air is making me run lean how do i compensate for it. lower the boost at nite? i'm running a inline fp and fmu for fuel i thought that was ehough fuel for 8lbs. and i'm only running 5lbs. as for the poor ground i'll try gas it with my lights off in the nite to see if i have a poor ground. thanx for the help so far any others? could something be mechanically wrong because it ran fine just until this past week.

 

is this something that happens to a lot of people? cuz I've never run into this before.

 

I doubt it's due to the cold weather....