terrible gas mileage 3.4L v6

just getting used to the new truck and gas mileage sucks!

it runs good and smooth except first thing in morning it idles a little rough at first until I tap the throttle then its smooth and stays that way.

I replaced the fuel filter, cleaned the MAF sensor, did an oil change and new air filter and only just because its a new to me truck, well the air filter was filthy dirty.

my first tank averaged right about 15 mpg but I don't recall the numbers

my second tank I went 190 miles and needed 12.75 gallons so that comes to 14.9 mpg (not great but reasonable)

my third tank I went 144 miles and it needed 15 gallons so that comes to 9.6 !!!! (wtf) conditions didn't change much as I recall but maybe I was driving more aggressive this time. but I also was playing with fuses so maybe I reset the ECM by mistake?

there is no gas smell in oil and everything seams fine with no restart issues so I don't think its leaking injectors or anything like that.

I need to replace the plugs and I still have to keep monitoring and get more tests to see if this was just a fluke but what mpg "should" the 3.4 get on average?

im not expecting the moon here but I was at least thinking I should get 17-18 mpg from it so im just wondering if its supposed to average 15-16mpg or should it do better?

 

I generally get around 15-18, Depending on how I drive... Those first two tanks don't look too abnormal but that last one looks really bad. Less than 10mpg is a problem. It may just be a fluke like you said. I'd monitor it for a couple more fill ups and see how she does.

 

I drive mostly city(about 50 miles highway and 230 or so city) and average 18mpg. I am a manual so I know that helps me a mpg or two, but still.

I don't know much about your new truck. Lift, tires, any upgrades?

 

its all 100% stock, no mods, no changes, its a prerunner with 265/70/16 tires brand new all around with right amount of air and the alignment is great, goes straight by itself forever.

my mileage is 95% highway 5% city so I was expecting to see at least 18 average with it.

maybe the new plugs will help, it was idling rough just now going to the store but only when in gear, sorta like my old 2.4 used to do lol.

do these things take special plugs? I saw something somewhere about double electrode plugs but I don't recall the subject talked about.

 

Yea it's a dual electrode plug... I believe they're made by Denso or NGK. If I were u I'd just get them from the dealer. They're not expensive.

 

ok, will do

are they hard to get at to change? the DIY thread shows a 4runner with a bunch of crap in the way

 

Not really hard to change, just make sure you have a swivel, spark plug socket, and a couple extensions. The hardest one to get to was the drivers side one closest to the firewall. It took me a little while to get that one back in. Just be careful not to cross thread them and use a little anti-seize on the threads.

 

https://www.tacomaworld.com/threads/the-truth-about-spark-plugs.152726/

I recommend either Denso or NGK. Both are OEM. I am going with NGK when I switch mine out this week.

You should be getting more MPG than 15. I get 22 all highway on 31 10.5 15.

 

OP whats the mileage on the truck? I know u said it idles a little rough, have you cleaned the throttle body? does the idle RPM seem normal?

 

idle rpm seams normal but I never noticed what it was idling at

mileage is 115k

and visably the truck seams well cared for other then the air filter looked like it was never changed in a long time so while the truck interior may have been taken care of, I have no idea how well maintained it was.

I cleaned the MAF sensor but when I took it out it already looked clean so I took that as a sign the intake system wasn't dirty

 

Well I wouldn't rule it out considering how dirty the a/f was, I would also do an induction service, something like seafoam or other top end cleaner you can run thru a vacuum line into the intake manifold.

 

yep, I haven't had it long enough yet to even replace all the burnt out light bulbs and replace the faded headlights but I will slowly get to it all.

timing belt needs doing as well but that will have to wait a while for now, they always recommend changing things long before they wear out so I think it should make 150k before it becomes a priority to do so im thinking I have time

 

I thought timing belt was 90K miles? Am I thinking of another vehicle.

 

I went on business it was 280 mile one way I averaged round trip right at 22mpg. City driving I average 18-19 mpg.

I would reset the computer, see if that helps.

 

Yea the suggested interval is 90k... I did mine at 85k because the truck was 12 years old.

 

I used to get 14 average but 15 now with a new muffler and 32s. Should I try a few of these things?

 

it is, im basing my thoughts on most dealer recommendations are to replace parts at 75% of their life expectancy so it assure no break downs for cases where it might run out of life sooner. so based on that I "assume" real life expectancy of the belt is 120k so yes I am pushing it but im not going to wait until it hits 150k I was just exaggerating using that number but some people do go that long, im just waiting until I have the time and money to do the job with all the other pressing matters going on right now so maybe in the fall after I put another 5-10k miles on it.

by the way it got decent mileage today just based off how far the needle moved so I think im averaging 15 now and that other reading was a fluke because I drove 80 miles with the computer reset to defaults so it wasn't optimized. I went 145 miles on a little less than half a tank burned

 

Ive got 170 k on my original timing belt. I get around 22 mpg if i drive nice. 98% freeway speed. I got 350 out of a tank recently..! Shocked me. Id do plugs definitely. Just get oem from the dealership. Dual electrode (i think electrode) cant hurt.. Its new to you than definitely do em. Or at least clean em. Wire brush and carb cleaner.

 

been there done that, cleaning plugs helps but its an exercise in futility and not worth it.

I will change plugs with oem dual electrodes even though I don't believe there is any benefit from an extra electrode but perhaps a slight minutia of longer life based on the idea if one side wears and the gap widens, the other can take over, that's about the only benefit I can think of since you only get one spark no matter how many electrodes you have

 

15/19.

http://www.fueleconomy.gov/feg/Powe...2004&make=Toyota&model=Tacoma 2WD&srchtyp=ymm

Many scoff at EPA estimates. Since their last formulary revision, I have found them quite accurate across 3-4 marquees. In fact, occasionally a bit lower than I actually got on a regular basis. So on a stock truck, they make a reasonable baseline.