Hey everyone, I've been getting horrible gas mileage on the highway, around 11mpg. This is in a 4wd 5.7 2008 quad cab with mds. One thing I noticed is that at idle I have great vacuum at 22.8 inches, but on flat road driving 55mph the vacuum reads as low as 3 inches. Anyone have an idea that could relate to this?

 

How many miles on it? What size tires? Has it done better in the past? How much better?

 

it only has 70k miles on it I have 17 inch rims. I pulled the oil cap and didnt notice any signs of blow by

Edit: I have only owned the truck since march. It was better when I bought it, but seems to have declined since

 

Original O2 sensors? Might try changing the front ones first, and see if that makes any difference. NTK or Denso sensors only please.

 

Just ordered a set, they'll be here next monday. I'll let you know if that fixes anything. Thanks for your help

 

When was the last time a tune up had been done?

 

About a month ago I changed the plugs, they were worn down a bit, but in they didnt look too bad, all the same. The MAP sensor was changed at the same time, without any change in performance.

 

Just tested it out on the highways with the new o2 sensors, I'm getting the same

 

How does it run? I only really expect to see good vacuum at idle, when the throttle is closed.......

 

the truck runs excellent, it just gets terrible economy.