That would have been nice......... I know I would certainly have appreciated it.

 

Well I don't think your missing much. I'm running 285 75 16's and only averaging 11.3 with no power. the only time my tires spin is if theres sand in the road, and I've tried.

 

A tuner is called for then.

 

I'd like to but can't really afford it right now. I checked the plenum out and it seems to be ok, pvc was not. I do however need to but a front o2 sensor on it. Original owner cut out the cat and the sensor with it.

 

I have the same truck you have but with 4:10 gears my gas mileage sucks but I do better than 8 and over 95% is city type driving BUT I am now getting almost 12....Heres what I did...K&N CAI system, Flowmaster 44, new cat (mine was busted up) and the biggest help I installed a Vacuum guage and watch it all the time and it has really helped!! Try these items and see if it helps I also have a set of headers that I am going to put on soon I hope that helps also with gas at almost 4$ a gallon I need all the help I can get......Good Luck

 

Have you corrected the odo/speedo for the larger tires? No? In an ideal world, you travel roughly 12% FURTHER per tire revolution with your new tires (34.4") as compared to stock tires (30.5").

Don't use the low fuel light to determine MPGs. These low fuel lights come on when there can be up to 6 gallons of gas left. Always fill the tank completely, then run it down and refill the tank full again and divide the number of miles traveled during that tank by the number of gallons needed to refill it on the pump.

So recalculating with the above data,
240 miles * 112% = 268.8 miles (due to the larger tires)
268.8 miles / (34 gallon tank - 6 gallons left "Low Fuel" light) = 9.6 mpg

Just how accurate are you in your calculations? 9.6 mpg isnt good, but it's 20% better than your original calculation. Do the other things posted by others to make it better.

Most people don't correct their gauges. I recommend doing so.

-JT

 

That's most of your problem right there.

 

sounds like you have an air leak, was the O2 voltage in the lower range when they where switching and compare the two sides against each other to see if it is a bank specific problem. check spark plugs and injector o-rings for a leak, spray some brake kleen around them and if the idle changes then you know where the leak is. also check leaks around the throttle body gasket and vacuum hoses

 

my speedometer is not corrected, and i have 3:55 gears

if i install a vacuum gauge, what is the best vacuum to stay at for best mpg

im going to run a tank threw it again and see what mileage i get, the tank i had now my credit card cut out before it was full, (stopped at 100 dollars) and didn't let me pump the tank till it clicked

also the truck is burning/using NO oil so i don't think my plenum is blown,

also i constantly smell antifreeze but i am never low on coolant

also i cant fix is after driving the truck for 20-30 minuets the belt starts to chirp, it becomes quite if the truck is placed into park, but R,N,D,2,1 it chirps. i have replaced idler, tensioned p.s pully because it wobbled, and tried 4 different belts cant get it to go awap

i don't know if this is a cause of anything but let me know

 

Higher the vacuum, better the mileage.

Have a look down your throttle body, just to be sure.

does the smell get worse when you turn on the heater? any evidence of leaks anywhere?

Clean the remaining stock pulleys. A bit of dirt makes a lot of noise.