Extremely Bad Gas Mileage

What’s up guys, don’t post much at all on here but occasionally come on to look around.

Anyway I have a 2006 Tacoma, 4 Door Prerunner 4.0L, and I’ve had it about a year. Got it as my first car, few months later engine light came up and head gasket was failing, water pump, etc.

$5-6k later and it’s fixed but over the last few months I’ve gotten average of 11 MPG which is f**king insane for an 18 year old.

Oil and filter is done, spark plugs new, entire top of the motor basically redone, fuel hasn’t been weird in the area, etc. Nothing comes to mind when it comes to what’s making my mileage suffer but I need something done.

Does anyone have any suggestions? I don’t drive it crazy, but I drive it a lot. Stock wheels/suspension.

Anyone with some knowledge of what could be making this happen, please help haha. Anything I need to check? things that go bad on Tacoma’s that will cause poor mpg?

Thanks, much appreciated

 

What kind of tires? Have you checked to make sure you dont have a dragging brake? Any armour added? When the HG was replaced were the injectors checked?

 

Breaks fine, were done not to long ago. Again, stock wheels and rims with the 06 Tacoma.

And yes, they basically checked the entire motor and put it through lots of testing before it was sent back to me.

 

Possibly bad or close to failing cats. O2 sensors. My 15 4.0L gets 22-23 mpgs with 80K miles. Is the air filter new? Clean your throttle body and mass airflow sensor. Don’t assume all that was done on the engine rebuild.

 

OP, how did you calculate your mpg?

 

https://www.tacomaworld.com/search/8508142/?q=gas+mileage&o=date&c[title_only]=1&c[node]=5

 

OP, I would suggest that you get a scan tool on the thing and look at the short- and long-term fuel trims (STFT, LTFT) and see what they show. You may have excess air (small leak) or something else that may be revealed by the O2 sensors pointing toward bad cats, injectors, etc.

 

ARB1977
How do you find out if your O2 sensor’s and cats are going bad? I have a 2010 and I get 15mpg

 

I've seen many people mention this but what are you looking for as far as fuel trims? What numbers are considered acceptable?

 

I get 10 - 12 mpg with 33x12.5x20 and a 6" lift. Stock I was getting a consistent 18-20 mpg. Check your spark plugs, coils, spark wires, timing, TB, air filter, fuel filter, and ensure correct oil levels and what not. Make sure your tires are inflated correctly. Do you experience a power loss? If so, that may explain the bad mpg. Check your entire exhaust system as well and ensure you muffler and cat are in good shape. If your cat or header pipes are glowing you have a combustion issue. Happened to me once in my old 3.4 taco

 

Haven’t checked cats or 02 sensors, I cleaned MAF sensor few months ago throughly, was gonna get on the throttle body soon.

Past 4-5 months I have been calculating every tank on how many gallons I’ve put in vs how far I’m able to drive. Simple stuff

In an auto class, ran scan every month with a very high end device. No codes for anything whatsoever, it’s odd

18-20 mpg would be a dream in my truck, I use it a lot and getting back into motocross so with this mpg, it makes me want to sell the damn thing. Near 5k deep in gas this year oof

Thanks for the info I’ll check all that

 

Charlie,
Where do you live? My commute is a lot of hills and then stop and go traffic so my mileage also sucks. It also doesn't help being young and hitting the throttle hard. Not to say you are a hoonigan, but it takes a while to learn how to drive mpg conscious.

 

Another thought - since the whole top end was R&R'd, it's also possible you have an issue with cam timing. That's an awful lot of mpg loss for it to be a small issue.

 

Here is quick and dirty and intended only to get you started:

Basically what you are going to do is hook up the scan tool with the engine warmed up and watch for a minimum of about 30 seconds each the short- and long-term fuel trim values at idle, 1,500 rpm and 2,500 rpm.

The STFT will be bouncing all over the place as it is constantly sending correction signals to the ECU but ideally you would like to see the numbers frequently flashing around 0 plus or minus 10%. So you will see things like +4, -1, -1,+2, 0, +1, -8, 0, +10, -3, -10, -1, +1, 0, -1, -2, and on and on.

The LTFT is the accumulation of all these rapidly changing values of the STFT and will show a a more stable number not rapidly dancing all over the place, but again ideally you would like to see the LTFT around 0 plus or minus say 5-10%, but the closer to zero the better.

And finally you want to know the Total Fuel Trim. Add the STFT and LTFT numbers to get the Total Fuel Trim. If the STFT is +2% and the LTFT is +4% that would be a total of +6% again near 0 is good. But watch the signs, if the LTFT is +10% and the STFT is -8% the total fuel trim is actually +2%.

Here is a much more thorough discussion and a good place to start understanding this on our trucks: https://www.tacomaworld.com/threads/understanding-o2-signals-and-fuel-trim.259164/