Seriously Decreased MPG - what to check/replace??

[WhiteHoeZ71]

Ok when I first got my Hoe at 20k miles, it was getting like 18+mpg in the city and 21 or so on the highway. Since purchase, the only mods Ive done that could affect mpg is bigger tires, (285's I think), Magnaflow muffler, and a Spectre cold air intake. Obviously the tires dropped the mileage some as did the muffler but it still stayed around 16.6mpg city. When I first installed the CAI it went back up to around 18 in the city. The intake has been on for about two months now and the mpg's have dropped to a ridiculous 11-13mpg in the city and 16mpg on the highway with cruise set at 74mph.
I know the first thing you're thinking is that Ive gotten a heavy foot since the CAI install but I assure you that is not the case!! These are the mpg's with me or my wife driving with our two toddlers in the car most of the time. I live in Louisiana so, my air conditioning has been on since early March not just recently. The hoe now has 69k miles on it and has nothing but Mobil 1 synthetic oil. Also, I use seafoam or the like in the tank every other oil change or so.
Besides the hard to access fuel filter, what would you suggest I try to regain some lost mpg's? Were taking a 1k mile trip to Orange Beach next week and really want to get something figured out before we leave. Thanks in advance!!

 

[hassoun]

thats what our trucks do. 11-13 city and 16-18 highway. your calculations were probably wrong. with cruise control i get like 20 on the highway but thats about it. maybe your 06 gets a little better i dont know. i have a 6.0

 

[My01yuk]

I'm coming up on a year of ownership next month so I may not be the best person to spew this out but here goes. Have you cleaned the MAF and TB? I don't know of anyone getting 18 in the city with these rigs. I avg based off of my hand calculation between fill-ups and not an on board computer because I don't have one about 13-14.5 in the city. I have a 4wd slt yukon sitting on 265/75/16 with new plugs, wires, fuel pump, drop in K&N, MAF and TB cleaned and can still only manage 13-14.5 in the city. A BB tune will probably be mentioned by others as Justin from what I hear is the man at getting the top performance out of our hoes and kons. Can't wait to get one myself. What year is yours? Mine is an 01. Hope that helps

---------- Post added at 09:56 AM ---------- Previous post was at 09:55 AM ----------

Never mind on the year of your truck, didn't look at your sig first time around.

 

[WhiteHoeZ71]

Thanks for the fast replies! I'm stating mpg from the DIC. I know 18 in the city sounds far fetched but it originally got that (according to the DIC). I test drove many Z tahoes before finding this one and it's the only one that had that kinda mileage. I did forget to mention that when I installed the cai, I did spray cleaner on the Maf and TB. Bb tune is outta the question for now unfortunately. It's a 06 5.3 btw

 

[almightys]

Try cleaning the air filter?

 

[M.M. 700]

I swear they put something in them at the dealer, that makes them get awesome mileage
I had an 02, traded that for an 04 with 29K miles. WHen I drove it home I reset the onboard fuel mileage deal. And was shocked it was getting (what it said) around 20-21 doing 60 mph.

Now with 73K miles it av. around 14.5-15 on the highway.....


You might try a tune up. Fuel filter,plugs, and plug wires......that is what I will be doing very soon.
Are you using the same type of gas? I know my mileage goes to chit when using ethonal......

 

[WhiteHoeZ71]

Try cleaning the air filter?

It's only two months old. Same gas as always unless Valero has changed theirs. I'm thinking I may try plugs and wires but according to the manual I'm 30k premature on that..

 

[TunasTwins]

Change your oxygen sensors, they're the bottom line to fueling. Your PCM will adjust fueling base on what they see. At 70k, you're due. Also, has the area you're in recently changed to E10 gasoline (10% ethanol)?? That will effect MPG also.