I have been having an issue with the truck getting poor fuel economy. I have checked the plenum and it seems ok, but what i was wondering is for the 5.9 what is the vacuum at curb idle? What is the best way to tell if the clutch is stuck for the fan? It has a new cat, rebuilt the engine, sct tuner

 

Sorry the truck is a exended cab, swapped in 5.9, 4x4

 

What's your definition of "poor"? These are basically bricks with an engine. If you are in low to mid double digits, you are doin' pretty good.

 

In the city im about 9 mpg and on the highway about 11.Thats cruse set at 65 That just seems a bit on the low side.

 

Lol that's what I get, just drive it like you stole it because the worst I've gotten in city is 9.4 and best is 10, it's worth .6 mpg just to have fun lol

 

The fan should spin easily when the engine is cold. Other than that they just get crappy mileage lol

 

How old, and what brand O2 sensors? Last time you did a tune up? What kind of spark plugs are in there?

 

1. Did you put new injectors in the truck? If you used anything but stock injectors, then that is your problem.
2. Did you do a tuneup? Cap/Rotor/plugs/wires
3. How is the exhaust? Not sure, but I would figure that the 3.6 exhaust (stock) is a bit narrower than what you need for the 5.9.
4. Do you have a paper filter or cloth filter? If you are still running a paper air filter, I would RUN not walk to autozone and get a cloth HpR filter from autozone for 25 bucks. Instant 1.5 MPGs.

I get 11 MPG city and 16 MPG highway (65 MPH, after that it takes a NOSE DIVE). But I have a few mods AND a cloth filter. Even my wife's Yukon has a cloth filter.

 

Hey you, Not sure on the o2 sensor same on when I bought the truck so i will get a new one and replace it. any sugestions on brand?
Cap, wires and plugs where put in about 3 months ago, used chamion plugs.
Cptafw163, They are the stock injectors, most of the exhaust is brand new as previous owner gutted the cat and it kept throwing the cel. It does have a paper filter so i will poick up a cloth filter. I guessing the truck is getting what it should.
Thank you everyone for all your help

 

If you really want to get gas mileage, but let a bit more dirt by, get this filter:

16 bucks from summit, or about 23 bucks at autozone.
http://www.summitracing.com/parts/EDL-1002/


It is just black foam. But it pretty much flows as much air if you don't have an air cleaner on there. If you change your oil every 3K miles, you should be OK. I would get one from autozone so you can inspect the foam as there are some holes in the corners. Nothing a little RTV won't fix though! Unless the RTV gets through and into your chambers.

I had that on my 1996 5.2 with a mopar PCM and I got 16 MPGs. It was a 4x4 too. But i had 33 inch tires, so that can take a bit off the gear ratio (make it numerically lower).