Did you check for a plenum leak?

 

12 sounds normal for a 360. what kind of plugs did you use? and is the new o2 sensor the downstream because it may be a bad one, sometimes new parts are defective. and i say maybe cat. get a heat gun and check the temp in front of and behind your cat. if its bad it'll be a lot hotter in front of the cat than it is behind it. and the heat guns are 20$ at advance, never checked lowes but i bet they have them too.

 

Thats my beat.

 

Have not replaced the wires. No misfires on scanner, so I feel like the wires could not cause such a fuel loss . Maybe wrong. Checked fuel pressure today while engine was running- thinking maybe regulator was bad and forcing fuel past injectors. Fuel pressure was a constant 48 even off idle- so fuel system passes the test.

 

you should replace the wires.

 

The wires may not be failing, but if the resistance is to much, they will not be delivering very good spark to the plugs. This could lead to increased fuel consumption and loss of power.

 

Subscribing to thread...

I'm trying to learn more about the 5.9L engines and how to get the most out of them too. (MPG wise)

I'm already getting 20-22 MPG in my Cummins diesel now to figure out how to do it in a 5.9L gasser... I realize I never can hit that high mark like the Cummins But I'm currently around 12 MPG and hoping for at least 16 MPG

 

There is another thread that has some good reading concerning this....
https://dodgeforum.com/forum/2nd-gen...eath-toll.html

I was in the same boat as you, and I just started changing things one part at a time at the beginning of each tank to see if it helps.
1. Plugs
2. Plug wires
3. Cap and Rotor
4. Tranny tune up (Yes, if it isnt shifting correctly, you will lose MPGs)
5. Air cleaner
6. Lower viscosity oil
7. Brand of gas
8. Octane level of gas

After messing with all of these, I saw a greater improvement by just switching to Shell 89 octane gas. Now, I average between 13-14 in the city, and the highest highway was 16.3

 

Pulled the plug wires. Found one out of eight that a slight diff. ohm reading.
Replaced plug wires anyway--- No change !!!
Any more guesses???

 

I'm not reading the whole thread, but 12 mpg is close to normal. Do you have any oil consumption along with the low MPG's? Check the plenum as stated above. http://dodgeram.info/tsb/2000/09-05-00.htm