So I'm consistently getting around 16 mpg on my dodge dakota. It's a 3.9L, and I spend a decent amount of my miles on the highway. Considering other peoples reports on herethat I am reading of around 19 mpg, I'm boggled about why I'm getting the results that I'm getting. I'm not even running my air conditioning to be getting 16mpg!

I've completely cleaned out the intake, and replaced the plenum gasket, did a custom CAI, went with synthetic oil, changed the filters all around, put in nice spark plugs, new spark plug wires, a new distributor cap and rotor... the list goes on.


So what's the story? What else could be responsible for my low milage? I'm not burning oil, I've got pretty good throttle response. I noticed my fuel injectors were a bit dirty. I purchased sea foam a while back to run through my engine, although I'm waiting to run it through right before my oil change. I'll also run it through a full tank of gas before I change my oil.

 

What spark plugs did you go with? I know the Magnum motors don't take kindly to plugs like the Bosch+2/4... good reports about some NGK's, and the plain-jane Champions.
Also, replacing the O2 sensor(s) may help. I know... their supposed to throw codes when they go bad, but you can't always rely on that.
What speed are you running at, on average, on the highway?
My trucks got the 3.55 axle ratio (and, extended cab, 4x4, 4 speed auto) with the same tire size as stock (235/75R15 in my case), running at proper tire inflation, I seem to get around 17MPG at 75MPH, with A/C on, and seem to addmaybe 1MPG with A/C off. My mileage seems to increase about 0.8MPG for every 5MPH I slow down.*
City, I average 12-13MPG, A/C doesn't really make a differance.*

*Figures are subject to change at any time, without cause, prior notification, or stated reason. Averages are shown, actual experiances may differ.

 

I'm a mixture of city and highway, probagbly 60 highway 40 city lately. I tend to be going 70 ish on the highway.

I went with some mid grade bosch plugs. Interesting to hear that others have had wierd results with them.

I'll consider replacing the O2 sensors. At $25 a wack or so, with 4 of them, that's a lot of sensors to be replaced!

I've got an OBD2 reader. If I posted a full readout would anyone maybe be able to decypher the information a bit more? I'd be interested to see if that's possible, and learn what made it possible.


I gotta go to work. I'll be back later.

 

$25 for an oxygen sensor? Where are you getting them, sign me up!! NAPA lists at least $50 for 1, and AutoZone ain't any cheaper.

 

I would love to see $25 O2 sensors too!!!!

I would have to guess that is the problem though.

 

Word, I guestimated off the top of my head. So... $200 to replace all 4 oxygen sensors, and not even a guarantee of better milage? Argh!

 

My 2000 3.9 regular cab gets about 18 average combined. Thats with the 3.92 rear gears through the 4-speed automatic with the stock size tires. I've heard a lot of bad things about Bosch spark plugs, never seemed to run well in any vehicle I have had. Prefer either NGK or Champion for a Chrysler product.

 

I think I would first pull those Bosch spark plugs. Seems like any vehicle I have used them in has had emissions or just plain running problems.

My 2000 Dakota automatic with 3.92 gears gets about 18 combined so you are not really that far off. One the highway, my trip computer shows it is reading about 25mph at 65 and about18-20 at 70. So combine your freeway mileage with your city mileage and I dont think your are doing too bad. Aveage fuel mileage is just that ..... average. Could be your driving habits, could be a maintenance problem somewhere. It's hard to say. I would try slowing down to 65...... if you can without becoming a semi trator grill...... for one tankful and see what effect it has on your mileage. I am willing to be that you'll get 18-20.

 

how did you "notice" your injectors were dirty?it would be microscopic dirt pluggin the end of the injector

 

i get about 19-20 on the highway w. AC on, but running 150 miles onm the highway and then 100 around town my mileage went down to the 14 range so your probably fine