Low mpg?

My '03 6 cylinder (I've had it a couple months) gets 15-16mpg. The cat doesn't meet threshold, are the two related?

 

that mpg is average.

I get SMILES PER GALLON

 

Maybe, but probably not. (yet)
A partially clogged cat can cause mpg loss.
As the engine has to work harder.

But the reality is, it's a 22 year old truck with a 3.4 engine.
The 3.4 never has, did, or will, get good fuel mileage. 16 mpg isn't bad.

You might look at the fuel trims on a scan tool, just to see is you are running lean/rich.

 

Is this 15-16 MPG mostly city driving? If so that's pretty normal. If its nearly all highway, then perhaps its a bit low. But don't expect phenomenal fuel mileage from a 5vz

 

Yes, possibly

Look for an intake leak. Like a broken vacuum line or leaking intake manifold gaskets. Check the intake duct between the maf and throttle body and make it isn't split open. What do the long term fuel trims say while driving around? Are they over 5-10%?

 

My 3.4 5 speed was used as a Truck Load in the bed and towing.

My normal mileage was between 10 and 12 mpg.

 

my 98 5 speed gets that in town. A little better when traveling below 70mph. The only reason I watch mine is to monitor engine components. If it goes out of wack something is amiss.

 

Have you done any basic maintenance on it?

Air filter
Plugs?
Throttle body cleaning
MAF sensor cleaning?
Fuel filter? (under driver side cab) mine was filthy.
What's your tire pressure ?

 

This came out of the fuel filter at about 120k miles.

 

This^^^^^. Then what ever mpg you get is what you’re going to get.15 to 16 mpg sounds good to me for your truck. Also we don’t know anything about your driving - mostly city? Mostly highway? Do you drive like a bat out of hell? What tires and size do you have. But in any event it’s a truck, trucks get shit mpg. No one buys a truck for mpg.

 

Out of curiosity, what mpg were you expecting to make you think 15-16 is low?

 

I had a '93 4 cylinder that got 20-21. Then an 05 that averaged around the same (4 cyl), and an 8 cyl. big F that got 18. I'd like to get 18-20 out of the o3. I'll start with the suggestions given here but like the truck so much that if nothing works then I'll just live with it.

 

please use some common logic here when calculation mpg. Don’t assume a v8 gets better has mileage, I can guarantee it has a much larger fuel tank size. Even the 05 has a 21gal tank vs the common 17gal for the 03 Tacoma.

 

that is filthy!

 

It is what it is and 15 - 16 is not that bad. I have a 2024 Frontier with less that 5k on her since I bought her new 7 months ago, 19.5 mpg freeway @ 55 mph and this is with all of the latest technology that is out there.

 

automatic 4speed transmission?

 

The DCs are all AT.

 

are they 4speed or do they have an overdrive gear
i have an MT 5sp so i am clueless

 

I can't remember. I had an Xcab 5 speed manual.

I test drove a used DC once, and IIRC, it is a 4 speed plus the ECT or whatever button that, in my test drive up a steep grade at freeway speeds unloaded, did...diddly.

That was the day I realized I was doomed to a 2nd gen DC, and because I could not deal with the idea of a SB, had to get the LB which ONLY CAME IN AT!

 

4 speed and 4th gear is OD