I always check my mileage when I fill up the tank. I've slowly watched it drop over the last couple of months. It used to get about 18-21 just driving it only in the city. I don't drive the truck a whole lot, and very rarely on the freeway. Never drive like a crazy driver and always shift when the shift light comes on. Nothings changed, just the mileage dropping gradually. I know there are tons of posts about tune-ups and such, but just don't know where to start. (obviously cheap though). I'm thinking it could be a O2 sensor or some other sensor (?) Any suggestions would help. I love this truck, it's my baby and want to get the best mileage possible.

*Note: I don't have a lift, or bigger tires, tire pressure is good, fuel filter and pump are good, Oil changed regularly with synthetic, air filter is new, only drive it about 5 miles each day. (to work and back).

151,000 miles, 22 gal. tank

 

When is the last time it had a tune-up (spark plugs, wires, etc.)? Have you ever changed the O2 sensor(s)? They start getting "lazy" around 100k miles. It sounds like you're already on the right track. Also, I've found that different blends of fuel available at different times of year have an effect on my mileage.

 

it could be due to the fact that its starting to get colder out thus taking longer to warm up, and if you only live say 5 minutes from work, your truck is not completely warming up. generally when a car is cold it will run much richer (dump in more fuel than needed) thus being compounded by the fact that its colder out. i too live very close to work and my temp gauge will barely moved from the bottom peg by the time park in my spot at work. I am getting about 13 combined in a 93 v6 reg cab short bed auto 2wd. ive just come to expect it. now granted it has 215k on the clock and is in desperate need of a refresher (this upcoming spring) so my mileage is a little skewed. but another thing to check is the Intake Belly Pan Gasket. basically look down the throttle body with a flashlight while holding the throttle all the way open, if you see pooled oil in the bottom, theres a good chance that the gasket has fail which is all too common on these things. ok im done rambling. happy hunting,
Chris

 

How are you calculating mileage?

Sure those tires aren't a little bigger than stock? They look like it.

Mileage is always worse in the "winter" because of the winter blend gas. Every October I can see my mileage start to go down and it usually comes back up around April. It isn't surprising that driving only 2.5 miles at a time results in crappy gas mileage

 

Tom A:
I haven't ever done a full tune up because the wires and cap and rotor don't really look that old, but I'm just not sure because I didn't put them on there. So I really can't be sure. That's a really good suggestion though to do a tune up on everything. Thanks! Don't know about the O2 sensor, that's what I thought it might be. And what kind of fuel mixture would you recommend for winter time? I just always put in the regular 87 octane, I think here in Utah.

Dodgeman1990:
I'll have to check that Intake Belly Pan Gasket sometime. Thanks for the advice. And that definitely makes sense that it's not warming up because I don't drive it very far, thus making the engine work harder and using more fuel. Thanks.


Hahns5.2:
You are correct, I forgot to mention that my tire are just a little bit larger, but not by a whole lot. Not enough to throw my odometer off. And with the stock tires I had on there before I still got the same mileage with them as I do with these. (Back when I got between 18-21mpg). Yeah the colder weather for sure makes it go down, but this has been happening for a couple of mouths now, so I don't thing the weather has all the blame. Thanks for you response.

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Hope I answered everything, and I forgot that every winter I put on a tonneau cover (bed cover) and that helps my mileage a bit and I don't have to deal with snow in my bed. But that only makes maybe 1-2 MPG increase if I'm lucky.

Thanks for the replies!!

 

i have never got as good of MPG as others. so iam really not one to tell others about MPG.. BUT DO plug the vent hole in the cap. JB-weld works good. trust me. took me 5 years to figure this out.

 

besides keeping moisture out, what purpose does plugging the dist cap vent provide?

 

The DC vent is meant to let moisture that might get in evaporate. I spray the inside of the cap with WD40, it drives moisture away from the contacts. I don't see how having it sealed would do any good. Moe7414 I expect you may have unknowingly had a bad wire connection at the cap and fixed it when you reconnected them after sealing that hole. They used to make all caps sealed and moisture was a problem hence my habit of spraying the WD when installing a new one.

I changed the cap, rotor and coil then added a can of seafoam to the 1/2 tank of gas and it made a huge difference in how my 94 3.9 runs.

 

if YOU have never done a tune up DO IT NOW before complaining about mileage or performance. From the outside they usually do "look" good... how corroded are the terminals in the cap or on the rotor? How worn out are the plugs? DO NOT use Bosch or anything gimmicky.
A tuneup is required MAINTENANCE not something to be :afraid to spend the money on"

 

all that said, tahts about what I got from my 94 2WD shortbed with its V6
Since I bought my 93 clubcab, I rarely get less than 17 MPG from it...
yet my 90 (pre Magnum) longbed (my 1st Dakota) I got 16 in town/combo driving and 20 on the road... I get 20 on the road with my V8... so why have a 6 when you get more power and better economy out of a (maintained) V8?