Back in May I installed a K&N cold air intake on my 03 Yukon (5.3L, 2wd, Corsa Exhaust) as a birthday present to myself. Ever since I've noticed that the gas mileage hasn't been that great. I thought it might have been the heavy foot, so I started watching how I drive, with gas being $2 a gallon and all. But even on trips, with the cruise set between 75 and 80, I'm only getting 16 to 16.5 mpg on the highway. Before the intake, I was getting between 17 and 18. Any ideas?

The only performance mod I have is the Corsa cat back exhaust. I'm interested in mods that increase HP and mileage, which I thought the cold air intake would. The Yukon is an every day driver, so I'm not interested in having a race truck. I just want it better/faster than stock. What other mods are good for hp and mileage? Besides superchargers. Most normal driving is around 2000 to 2500 rpms, so what gives more hp down low?

I just reinstalled the factory intake yesterday, and mileage apears to be better. I'll know more after a few days of driving. Thanks for the info.

 

I have seen a dyno run before and after a cold air intake install and the HP increase was only, and not quite 2 HP. At over $200.00 this seemed to be a shame to me. Poll a few dyno shop owners and you may hear some similar reports.
I run a K&N filter element just for the convenience of getting a consistent air flow, and perhaps a little CFM increase, and long intervals between servicing. Paper elements start loosing CFM from day one. When subjected to wet weather moisture, they dry and harden some. Just like a bullet out of a gun barrel, dropping and loosing speed the instant it leaves the lands and grooves. The K&N elements filter and flow better when dirty than a paper element does new.
I would figure the Corsa system to lower the mpg. Maybe it doesn't flow too much more than OE. I put a Gibson single in & out Cat back on a 97 Z71 5.7 and it was a drastic mistake. I lost low end that was noticeable immediately, and gas mileage dropped 2 to 3 mpg. And advertised as the quietest Cat Back on the market, it still resonated too much for me in the cab. They would not make good on it. It hit the dirt and I lost $$ and learned. Too much flow for what kind of HP you are generating will make you suffer.
I have a Nelson 93 octane tune (see my signature) and it is the best money I have spent for a performance mod for my application I have. It runs much stronger now. It also increased my mileage by at least 1 mpg highway. I have electric cooling fans and they helped my tight city driving by 2 mpg and keeps my AC nice and cool @ stop lights and bumper to bumper traffic.
Note: Before installing a new K&N element I let is sit out indoors, covered, on some news paper incase there is too much oil in it. Then after I run it a couple of weeks I remove my MAF sensor and carefully clean it with contact cleaner. Any oil build up on it will make the MAF lie to the pcm with negative results. After that it's good to go until it needs servicing.

 

The air intake flows more air, so wouldn't the computer sensors measure this and increase the fuel to match??? I've always thought this, but i've been wrong before and i'll be wrong again.

 

With mine i saw a 1-2 mpg increase but ive heard that it takes up to 100 miles for the computer to adjust itself. I dont know how long you had it on there but that might be it.

*edit* just realized you got it in may. so nvm

 

I tried a FIPK,it cost me power and mileage,took it off after a week .i like the UPD

 

I would say that there is something going on with your PCM. K&N FIPK's are made to make power. And that power may be costing you the gas mileage. I would have your PCM checked out as it is probably sensing something that it is having a hard time adjusting to. Just my opinion mainly because what I know of K&N and their FIPK's.

 

The FIPK doesnt seal against the hood,it sucks in hot air from the engine and the tin box heats up, also
i do belive a lot of people that use them think they are getting more power from it because it make more noise.

 

That is really odd. My mileage went up 1 mpg in the city and 1-2 mpg on the highway. The only other mod I have is a single flowmaster 3" muffler

 

Sometime the filter oil from the K&N gets on the MAF sensor.Might want to check this out.Have herd you should let a new K&N drain on a news paper for a few days before install.
FWIW

WP

 

I personally think it's ALL in the stock airbox.

I noticed a lack of tip-in, or off idle throttle responce when I started modifying my stock airbox, or running aftermarket intake boxes. The throttle responce got soft, indicating that fueling was not correct.