I have a 2000 Dakota, 3.9 with 113,000 miles. I drive 55 miles to & from work everyday, all interstate. I’m getting 10mpg 😖. I purchased this truck 6 months ago and replaced serpentine belt, tensioner pulley, plugs (dbl platinum) and wires, distributor cap, air filter, oil change, new Yokohama tires & tie rods. Check engine light displayed small evap leak and #5 misfire…I pulled #5 plug and the gap was very narrow, went ahead and replaced…checked my spark and it’s more yellow/orange than blue. Codes are clear, no check engine light and still 10mpg (I drive with a light foot).
the truck did sit for about a year (outside) and didn’t get driven much by previous owner because of health issues…any suggestions???
all are appreciated.

 

What's the tailpipe look like? Black?

Without more information I'd be saying look at the MAP or O2 sensors.
You'd need a scanner that can read them.
Whatever you do, if you need to replace them, do NOT use Bosch. Dakota's hate them. Go OEM.

 

tail pipe is normal. What other info do you need to narrow down my petro bogarting culprit?

 

Values from the MAP sensor are the primary controller of injector pulse width - think running rich/lean.
Values from the 02 sensors also affect the injector pulse width.

Are the injectors leaking? Poor spray pattern? How's the overall health of the engine, compression?

You didn't mention changing the rotor with the distributor cap.

 

I did not replace the distributor, just the cap.
I’m pretty confident it’s running lean, there has been a handful of times when I can smell a strong scent of fuel while idling.
Going to use my multimeter to test the 02 sensors Millivolt range

 

Not the distributor, did you replace the rotor?
A strong smell of fuel would be rich. Or a leak.

 

Most likely worn/offset upstream O2 sensors (as mentioned, stay NTK OEM) and/or MAP sensor. Any vacuum leak will raise MAP pressure which will command more fuel.

 

For what it's worth, I checked mine and it used 11.3 gallons to run 151 miles, so 13.36 mpg.
2003 3.9 V6 Standard Cab 3.92 rear, 4 speed A/T, 111,573 miles.

 

Dirty MAP sensor, vacuum leak, leaking injector(s), bad O2 sensor, clogged cat, thermostat stuck open, IAT sensor bad, leaking valley pan gasket.

 

Wouldn't any of the above issues create a check engine light/codes?
What is a real life mpg expectation for the 3.9 V6 Automatic?
Mine runs good, I don't really put a lot of miles on any of my
vehicles anymore, so mpg is not a huge concern, but I do want to
know if something needs attention...

1969 VW Beetle
2023 Cadillac XT4 Sport
2003 Dakota 4x4