outlaw08

I have a 2008 4.0, and I always got decent mileage with it on the highways, usually 27-30mpg. I drive to PA and MI and KY all the time, so I am pretty easy on my gas. About 2 months ago I put an Airaid CAI on, hoping to boost my mileage. My first trip to MI i was getting 32. On the way back down to KY it dropped to 28. Since that trip, it has been dropping steadily with no signs of stopping!! Just took a trip to PA to my fire house this weekend, when i first filled up I was getting 25 mpg highway. Next fill up 24, next fill up 23. I have dropped to 22 mpg in one trip! and have dropped about 8mpg in the past 2 months. What is going on?? I cleaned the mass air flow sensor and it did nothing. Is it an O2 sensor. Thanks for the help.

So_Cali

When was the last time you replaced the fuel filter?

outlaw08

About 3500 miles ago. And I also just replaced the factory plugs with OEM motorcrafts and gaped them to .054. The plugs were about 1300 miles ago.

Chromeshadow

How many miles are on your 4.0? What did the old plugs look like? Did you oil the filter with the proper oil? Is there a chance you used too much oil? Do you have any air leaks in the CAI?

aaquib1992

You said you put a CAI on it? Did you install a tune for the CAI? Even the ones that advertise "tuneless" usually make the engine run lean so your car is probably pumping more fuel to try and account for the extra air flow. Try removing the intake and running the car for a few tanks of gas.

ALWAYS get a tune before you go with a CAI, as that intake adds almost NOTHING in terms of power by itself. If you wanted better mpgs you should have gotten a SCT tuner with a mild tune (bama, brenspeed, etc.) and run that.

Chromeshadow

btw, if you remove the battery for a while the computer will go back to the factory defaults. It should take about 15 minutes of running after hooking the battery back up for the car to try to retune itself. I'm not sure if this happens when you get a "tune" . You can tell if the engine is running lean, the plugs will be white not light brown. If the plugs are dark, engine is running rich.

outlaw08

Chromeshadow- I have just over 41xxx miles on it. The old plugs were a little white. I will probably pull one of the plugs now to see what it looks like. And seeing as i have only had the intake on for about 4000 miles i didn't think i needed to oil the filter. And I also have tried the battery trick a couple times, and it hasn't seemed to do anything.

aaquib1992- I didnt want to put a tune on my car so i got the CAI seeing as many people say they have had no problems and didnt need a tune. guess i am the unlucky one, haha. I just took the intake off like you said and put the stock on back on. I know that it could have made it drop mpg, but i didn't think it would be that much. Would not having a tune cause the mpg to continue to drop? And if i did get a tuner, would it bring my mileage back up to what it was?

Thanks for all the help guys, I really appreciate it.

outlaw08

Oh yeah, I only care about fuel on my long trips at highway speeds, usually 10+ hours each way. And going from about 30 average to 22 is kinda a huge problem for my little wallet. I am spirited when around town though, use to get 14mpg. Or if running fire calls, 9mpg

aaquib1992

A few people on here do run tune-less CAIs but I cannot attest to their helpfulness. The tune is what will give you better MPGs BY FAR, it changes your timing/air to fuel ratio/etc. to give you some more power and better response with the transmission if you have an auto (changes shift points).

You should really look into the tuner to go with your CAI, overall a much greater benefit than just pumping more air than the ECM knows what to do with.

outlaw08

So if i understand right, if i put a tune on my car now, it would bring my mpg at least back to what it was before and hopefully more? How is the Bama SF3/X3 tuner off of american muscle?