I've got 65k on my truck now, and up until about 50k I could easily get around 18 mpg's going back and forth to work (60 mile commute). I started noticing a decrease in mileage around the 55k mark, but nothing significant, just figured my foot was getting a little heavier which it does from time to time, however it continued to decrease, and then I got a couple of tanks in the 14's.

I took it into the dealership they suggested a couple of things, change spark plugs, injector cleaning, and I believed they flashed the computer also. Anyway, I allowed them to do the injector cleaning, but not the plug change as I had changed the plugs at 45k, and didn't think they could be bad already.

I drove for a couple more tanks, no change in mileage. I decided to humor the thought, and changed the plugs myself, also I pulled the TB off and gave it a good cleaning, and pulled my K&N off and cleaned it up.

Nada, zip, nulch... No increase.... I'm starting to get a little concerned. That extra 100 miles that is coming out of my tank is starting to cost me.. You guys got any other ideas for me to check???

 

My mpg also went down after I changed my plugs, and I have done all the items you have mentioned and I 'm still not getting any where close to my old mileage numbers with the old plugs.

My only thought is try a new gas staion, or switch brands, or go for a good cruse on the highway, ie blow the carbon out ...

 

well wut kind of spark plugs are you guys usin? supposedly the higher end spark plugs hurt your truck more than help it out... i think we're supposed to be using the copper headed plugs

 

I use OEM Champion copper plugs... Same as what the factory put in..

My gas mileage didn't go down right after I changed plugs the first time. Actually I saw a little bit of an increase if I remember correctly... I actually hadn't done anything as far as mods or maintenance from the 50k mark to just recently (well, other than oil change here and there).

I used to get this kinda mileage with a trailer behind me using tow/haul and that was understandable. I'd hate to see what I'd get with a trailer behind me now.

 

I have also been getting terrible mileage. When I bought my truck I was getting around 14 to 15. Not good but better than it is now. As of now I'm getting about 10 and a half! I don't know if those fancy new E3 plugs would help me or hurt me but I'm thinking of trying them.

 

when you changed the plugs ...did you gap them ALL to spec or just throw them in??? if one or two are not gaped right... well ther is your problem.

 

Have you considered Ethanol?

I had the same thing occur to me early this year. I had just changed the oil or something .... right around the 40K mile mark. So I started chasing things like plugs, O2 sensors, filters, oil. Then one day I was looking at the gas pump and noticed the ethanol sticker ... then realized it had been there for several months and pretty well corresponded to my loss in mileage.

The only thing I have not done that I will do to kill my curiosity is to check out the EGR valve to make sure all is ok there. I cleaned TB and components, checked air pressures and all. Only explanation I can find is the Ethanol.

 

Ethanol will make it worse -- less efficient than gasoline.

 

A lot of stations are still switching to gas with up to 10% ethanol. If you were getting 100% unleaded and now you are getting 10% ethanol and 90% unleaded that would cause a loss in mileage. I have experimented with two stations, one that has 10% ethanol and one that doesn't. I lose about 1 mpg with the 10% ethanol blend. It sucks because now there is only one station here that still sells 100% unleaded and its on the other side of town.

 

Yes, I did gap all the spark plugs to spec, and the ethanol doesn't come into play as my local gas station does not use a blend. I have tried different gas stations, I'm having the same result with all.... If it was just a 1mpg loss, I probably wouldn't be too upset, however I've lost 4mpgs over the course of about 3 months...