Derf00

+1 if the mpg returns with the stock airbox then you know the issue is the tuneless CAI.

Nuke

Many things can cause loss of fuel mileage: dragging brakes, low tire pressure, clogged cats, bearing gone bad, higher ethanol content than what you were runniing before.... the list can go on and on. First step is to rule out a mechanical problem or, in your case, I'd put the stock airbox back on just to see how much of that is from the CAI. And since a CAI w/o a tune is near-worthless anyway,...

outlaw08

I decided that I am going to have Ford run a diagnostics on my car, even though it isnt throwing any codes and I will also have them run a fuel system pressure test. My mileage has gone down even more now with the factory air box on. Still have no idea what it could possibly be.

aaquib1992

Interesting. Are you positive you aren't driving it any harder or with more throttle than usual? How many MPGs are we talking about here? Because a few (1-5) MPGs can mean just about anything from different gas (ethanol content, etc. will affect mileage), to a slow leak or something of the likes.

Has the outside temperature changed in your area recently by a large amount since your last test?

SCCAGT

Unfortunetly, this will only serve to empty your wallet even further. With no check engine light on, more than likely, there are no codes stored in the computer. All they can do is LOOK at the readings from the MAF, fuel trims, O2 sensors, etc. If they are within specs, and I'd wager they are, it will be a fruitless endeavour. Excessive fuel delivery has many causes, but the computer would end up limiting injector pulse width, causing misfires since the entire A/F ratio would be getting messed up. That would turn on the MIL. But since the light is not on, the computer is not seeing any problems.
If fuel pressure were low, you would have driving problems as well as a loss of power, and misfires.

Nuke and aaquib1992 are more in the ballpark with what is causing the mileage drop.

outlaw08

aaquib1992-
I use to get 28-30mpg highway, that is 70 with cruz on driving 7 hours. Put the CAI on, it went up to 33. Then it started to drop, and has been dropping since. Just filled up today, and did the math, I was getting 21 highway, same conditions and driving habit. I also just put the factory intake back on and went for a drive after I filled up. I only went 94 miles at 70 mph w/ cruz, but I managed to get 24.7mpg. It went up some, but not to what I had before.

SCCAGT-
I didnt think that taking it to the dealer would be helpful, but i was desperate to get some of those 8mpg's that I lost back. It went up a little with the factory box. Only driving and time will tell.

Do you guys think that it was just this Airaid CAI? It said I didnt need a tune, but would it really cause my mileage to continue to plumett? I will have to drive more to get the computer to readjust to the stock airflow. I hope that is all the problem was.

Thanks again for all of the help

BigDinTexas

CAI = (supposedly) More Air @ given RPM = PCM adds fuel to prevent Lean condition @ given RPM = lower MPG

That is how I see it in my head anyways. Now for it to dip that much is bit strange. Did it seem more peppy with the CAI on atleast? Also, since you were traveling, the ethanol percentage was could have been higher from what you are normally getting causing a loss of MPG. Most around here is 10%, but some can have upto 15% if I remember correctly.

Don

outlaw08

Oh yeah, it was like the car woke up with the CAI. Now going back to the factory box, I can really tell how much it helped with performance. It isn't nearly as responsive, but that's how it should be without the CAI. I just couldn't handle the continuing drop in mpg's at highway as I drive about 2500 - 3500 miles a month. Around town I could care less about fuel, but not on long trips. I am still not sure if taking the CAI fixed the problem or not. I have been talking to every mechanic I know, and I am pretty mechanically inclined. But this fuel problem is over my head.

outlaw08

Sorry about not being posting for a while. I wanted to run some tanks through to see if that would change anything. The mpg has been steady at 24, which is still lower than before. Plus the car feels pretty sluggish especially when getting up to high way speeds. There are two things that I can think which would be wrong, the first being an O2 sensor which is going bad. If it is a bad sensor, I am assuming that it would be one of the two before the cats, is this correct? The second being a clogged cat. Would those two problems make the most sense? I have checked everything else but those. How do I check the cat, and is there a way to clean it?

Hope you guys help me out with this one as I have done everything but those items.
Thanks again, any bits of advice are greatly appreciated.

White05GT

A clogged fuel filter will lower your mileage. You might have got a bad tank or two of gas on your trip.

What brand did you replace it with?