I have a 98 dakota with 118K miles the big V8 etc, I noticed the milage was poor (around) 14 or less on some days, so I replaced the Ox sensor, I'm now getting 15.5 MPG, I think I should be getting better, I've always taken Very good care of the truck, as far as oil changes and etc, how can I get better MPG, I heard cleaning the Throttle body would help, it's due for a tune up.
Oh yeah, after replacing the Ox sensor it's cold blooded, and tends to stumble untill it's warmed up.
would replacing the after cat sensor help?

 

Are oxygen sensors that expensive? Seems like they should be replaced in pairs, eh? I'd go ahead and swap it out ... I mean, If 1 new oxygen sensor gave you +1.5 mpg, then 2 should give you +3 mpg, right?? [sm=confused06.gif]

Anywho, run some Lucas Fuel System Treatment thru, finish the tune up and see where that puts you.

Also, if you do mostly city driving, you probably won't get too much better mileage!

Good luck [sm=icon_cheers.gif]

 

o2 sensors can be expensive $60 bucks for the pre cat.
I think unless the computer gives me a trouble code, I'd rather not replace the post cat, course I haven't had the truck on the diagnostic since I replaced the O2 sensor, so It could very well be giving me more codes.
I put some injector cleaner and water removal in the tank, as I let the truck sit for a few months, next will be the wires and plugs , pcv and possibly the throttle body injector, last time I went from 14 or so to 18-19 MPG when that got cleaned, it lasted 5-6 months, but hey
with gas almost 3 bucks a gal now, it's worth it.

I yearned for the days I got 21 MPG with this truck, course it was on a trip to cal and that's downhill from here, Pacific Northwest LOL
didn't do that well on the way back HA (it was uphill what do you think)?

with a 5.2 L V8 I was delighted, course now I'd have an orgasm

 

The first O2 sensor tells the ECU what the A/F ratio is. The second O2 sensor just tells the computer if the cat converter is working properly, it doesn't adjust the mixture at all.

And your 98 should be MPFI not TBI, unless I'm mistaken.

 

Your right it's MPFI, I just looked.

So what the heck did the tech clean out the last time I took it to the dealers for a tune up (years ago)
I vaguely remember him saying throttle body, maybe he meant the rail system, as it took some special solvent and a few hours to clean it, I do remember it gave me better MPG for a few months.
I really love this truck, it's so comfortable, sound system is great, not a lot of problems, although I had that wiring crossfire when I first got it, I found a recall notice, and had their tech do a complete reroute of the plug wires, but this system is extremely high voltage
and it still does a miss once in a while, I'm gonna try those bosch plat 2's, so I don't have to worry about getting the gap exact.

 

even though your motor is MPFI it still has a throttle body. The throttle body does not have any injectors just throttle plates to control the intake airflow.

 

Man, I'd be happy with 18mpg. I do mostly city driving and regularly get 14 - 15mpg with the 3.9 in my 2003 Dakota. It's been that way since it was new. On the highway, I can get 18mpg. Once last year I calculated 21 mpg, but I'm thinking that was a calculation mistake. I've never got close to that again.

 

Dodge trucks arent exactly known for good mileage.

 

I think it may be an altitude setting, my engine should get 18 21 MPG, if set right, I checked the plugs and it's running rich
it may also be a fuel injector issue, I know it has a miss , just can't figure out what's causing the miss.

at one time I got 21 MPG on the way to california even 22 MPG, on the way back it still got 18, course that was when the truck was pretty new to me.

So my question is this, is there an altitude setting that allows for different elevations, or is that completly controlled by the Engine computer

 

The tech probably cleaned the throttle blades in the throttle body itself.

The ecu should control A/F and adjust for altitude by reading the MAP iirc, if the air is less dense then the pressure is going to be lower, right? Anyway it's going to be a function of the ECU.

Have you done the obvious and replaced the air filter?