Help! Terrible Fuel Economy

Hi, I bought my Tacoma (V6, 3.4L) a few months ago with 89k (now 91k) on it and have been fighting check engine lights for the majority of that time, which I believe I have finally fixed but won't know until my OBDII scanner comes in from Amazon.
To the point:
I have read about people with my same model getting up to 24MPG! On a good run, I'll average 14MPG. Now, I realize that 24MPG is pretty crazy and I'd be ecstatic just to get 20. The highest I've ever seen was 17 and that was right after a friend and I changed the sparks. The most recent runs have given me that 17, then 12.6, then 13.5, and now that I'm trying some hypermiling techniques, I'm on the path to get 15.3. Still, I should not have to go through so much trouble to approach figures that are still 10 mpg less than the listed manufacturer maximums.

What I know and have done:
- changed spark plugs, originals were factory (yikes)
- cleaned MAF sensor twice, once with MAF sensor cleaner, once with isoprobyl alcohol (after the dealership guy freaked out that I cleaned it at all)
- added coolant (P0125 code)
- shut my filter box which had mysteriously opened (probably the cause of the 12.6mpg)
- changed both my O2 sensors, which I now realize was probably a waste of money, but those related codes don't show up anymore so idk
- replaced all cabin lights with LEDs (rear, top brake light having issues I just noticed, but I can deal with that)
- Filter was cleaned out with a compressor when sparks were replaced

- Oil was changed right before I purchased.
- Exhaust seems rather hot and very moist, no matter if I have just turned on the car or driven it several miles.

I have been briefly looking into getting a cold air intake system thinking that maybe it will help by a couple MPG (even 1mpg would be worth it), but I want to know what others think before I spend more unnecessary money. I also looked into HHO, but it seems to get legitimate results, you need a programmer, and those are way too much $$ for me.

Again though, I shouldn't need aftermarket mods to get close to manufacturer specs, right? Please give me suggestions - what I can clean, what I can look into checking for replacement, etc - this has been driving me crazy (no pun ), as part of the reason I bought this truck was to get better fuel economy than my Ford Ranger.
Thank you guys

 

Have you actually replaced the air filter?

 

15 to 18 is more average for my truck. The best I ever got was 20.5 on a mostly highway run.

Are you doing city driving? Lots of short trips? What size tires?

 

I have not replaced the air filter. This may be a naive comment, but it looks new.. still white and everything.

 

I do almost all city driving, maybe a max of 10% is on the highway. If I could see consistent 18mpg, I'd be satisfied. Does 21 sound right for the tires? They are 204, 60H, W21 and All-terrain

 

City driving kills MPG.

 

I'm aware of that. I have made all highway trips and the numbers aren't significantly better, unfortunately. Any idea why it would spike right after the spark change?

 

I'm wondering if maybe the MAF is bad and that's why the cleaning isn't helping.

 

Possible I suppose. Is there any way to tell before I spend $50+ on a new one?

 

That I'm not sure of. May be some way with a multi-meter but that's above my pay grade.

 

Well that's actually more my forte. I'll look more into it and report back. Thank you

 

Congrats on your purchase! Though, there is definitely something wrong with your truck. Start with basic stuff first as always....Check for unattached hoses and look for large noticeable cracks. Make sure both hoses and connectors are plugged in. Check all fuses in the truck, both under the dash and under the hood. When you get your scanner, be mindful of pending codes and report back all the codes you read. If you dont find anything there, start changing basic stuff (which isnt a bad idea to do when you first buy a vehicle).

-Oil Change/Oil Filter Changer
-Transmission&Transfer case Drain/Fill (If its an auto and it fluid is brown/smells burnt, drop the pan, clean magnets, and replace filter if necessary)
-Differential(s) Drain/Fill
-Brake Flush/check (check the pads and shoes, then bleed brakes.. brake fluid is cheap and its just good insurance to know your fluid is good)
-Clutch fluid bleed (If you have a Manual of course)
-Grease Driveline (check for torn boots)
-Replace Air Filter (just do it... lol, dry paper filters are easy to maintain and you dont have to worry about getting oil on the MAF)
-Replace Fuel Filter
-Seafoam engine through intake
-Fuel additive through tank
-Clean throttle body
-Check PCV Valve, replace or clean if necessary
-Change coolant with correct stuff. Dont mix colors (https://www.tacomaworld.com/threads/toyota-red-antifreeze-coolant-aftermarket-selection.300926/)

Rockauto.com has great prices. Just watch where parts are coming from and try to get parts from one store only so you only pay shipping once. I like to order extra parts so ill get like 3-4 air filters, 3 sets of spark plugs, 3-4 sets of windshield wipers, brake pads/shoes, extra bulbs for all the interior and exterior lights (super cheap there). I would also includ a timing belt kit as I will eventually have to do one that (probably). Standard intervals for the timing belt are 90,000 but I believe most (or at least alot) of people go well past that. There are a few trucks with 250K+ miles on the original timing belt. I'm at 145K with original timing belt. I'm not sure I've heard of one breaking. Also, the 3.4L on our trucks in a non-interference motor so IF it breaks, your valves will NOT get smashed by the pistons. You'll just need a tow from wherever you are, and a new timing belt of course. Be sure to get a new waterpump, drive belts, thermostat, and oil seals too. Check this link for reference below. Oh and grab a clutch kit too just to have on hand if you have a MT.
https://www.tacomaworld.com/threads/best-timing-belt-kit-recommendations-pls.378817/

As far as the cold air intake, do a brief search in the 1st gen forums on the "deckplate" mod. It essentially cuts a whole in the stock airbox before the air filter to allow more air flow. The stock intake and the deckplate setup both grab relatively cool air. You may want to look at doing a Warm Air Intake however if you live in a really cold climate. Generally, a CAI (colder denser air = more oxygen) will get slightly better power, while a WAI (warmer less dense air = less oxygen) when get slightly better economy. The ECU will adjust fuel trim based on the amount of oxygen the motor receives so, less oxygen = less fuel used and vice-versa. The deckplate mode will allow you to return your airbox to a stock setup by screwing in a cover, it also allows a access port to send warm air off the exhaust manifold to the airbox by way of a dryer vent or similar.

I normally avg 17-18 on my 3.4L 4x4 MT. City or Highway driving doesnt affect me too terribly much. I did manage to get close to 22MPG from a tank, mostly highway with cruise control set at 50mph.

 

What plugs did you use? Toyota recommends only 2 types for your truck the 3.4L 5VZ-FE engine. I wouldnt use anything else other then the two below, if theres something else in there, I'd recommend replacing them regardless how new they are. They are super cheap on rockauto.com
DENSO

$18 K16TR11 Spark Plugs, Pack of 4

K16TR11
NGK

$6 BKR5EKB11 NGK Spark Plug Stock # 3967

BKR5EKB11
Gap both to 1.1mm or 0.043in

Did you use Denso O2 sensors?
DENSO Part # 2344162 Upstream; Automatic trans.
DENSO Part # 2344161 Upstream; 4WD; Standard trans.
DENSO Part # 2344153 Upstream; RWD; Standard trans.; DLX Model

 

If you are battling with check engine lite and fault codes then instead of throwing parts at it get your scanner, read the codes, determine the cause and repair as needed and for the price of an air filter just replace it. CAI, throttle body spacers, will not help enough or at all to justify cost As for tires A 60 series at tire is not conducive to good mileage and has your odometer been calibrated to the tire size? you may not be calculating mileage using accurate numbers. Last but not least Taco's are not noted for stellar gas mileage especially in city driving.

 

bawilson21, wow that's a lot haha.. I probably wont be changing the belt anytime soon, but you're right, I probably should pick one up since I plan on driving this to the ground. As for spark plugs, I got the cheap coppers from O'Riley. I'm totally willing to get the recommended ones, but what should I do with the ones I just got (literally like 2 weeks ago)? Is it really that important to stick with OEM parts like on the O2s?
I live in Arizona and the highs right now are creeping over 110F, so...just so you know.
Everything to do with brakes should be fine, I just had them checked out a month ago.

I'll definitely look up that mod and whirl through all the stuff you've listed. It's gonna take me a while though haha, half of it I've never heard of

I have no idea if the odometer has been calibrated. The previous owner had next to no paperwork for me and I hadn't the knowledge to ask of such things. How would I find out?

 

Spark plugs kinda are important, but they are cheap (if you know where to go). Try and return then but I doubt you can.. It would be neat to see how they affect your performance after you make the switch to the Densos or NGKs. From what I've gathered, it really is important to stick with OEM plugs and sensors. At the very least, make sure your plugs are double tipped.


To save money, I recommend shopping online only. The markup at the auto parts store is pretty substantial so I would only go there if you need a part ASAP, or you want something with a lifetime warranty. or no other place can source your part. Occasionally however, sometimes youll find a part cheaper at the local parts store. I get oil, brake fluid, windshield washer fluid, transmisssion fluid, and additives(marvel mystery oil & Seafoam) from Walmart. Otherwise, my goto places are: Amazon.com Rockauto.com Ebay.com
Do a search and compare the prices. If you dont need it right away, you can save money buy buying online. If you're super cheap. Copy the link of any item you want to buy on Amazon, and paste it into camelcamelcamel.com and it will show you how the price of that item changes. It may help to wait a few days (or months on an item you wont need for awhile) to save some money.

I was stationed in Tucson for a few years so Im familiar with the heat. I wouldnt worry about doing a WAI, but I would look into the deckplate mod to get comparable CAI results. Its about $10 and you can revert back to stock in about 30 seconds if you wish. I agree with @bubbabud, in that you should read the codes off your truck, and go from there.

I promise you your speedometer needle is off. Most Tacomas report 2-3mph slower at 60mph. Your ECU (and odometer) should read the correct speed however if you run stock size tires or you've re-calibrated. Get your phone or GPS and compare your GPS speed to the OBDII speed. Or do it oldschool and time your run at a speedometer check section of the highway. This

for Android Phones ONLY - Wireless Bluetooth Diagnostic OBD2 Scanner Car Code Reader and Scan Tool for All 1996 & Newer Vehicles ELM327 Compatible OBDII

bluetooth OBDII reader can connect to your phone using the free android Torque App and will give you all the readouts youll need. If your ECU/OBDII readout is off from the GPS, you may want to recalibrate your speedo, which i know nothing about. Compare your GPS to your speedo at different times incase the GPS accuracy is momentarily off (can happen due to solar events, but not usually)

 

First of all, thank you.
I don't believe that the spark plugs I bought are double tipped, so I will definitely order some from rock auto ASAP. Almost all I do is online and those 3 sites you've listed are my go-tos.
That's a good plan with the smartphone and the OBDII I have coming is of bluetooth variant for that exact purpose (Torque). Next time I'm buying from Amazon, I'll pick up one of those 4" deck plates.

 

Excellent. Im curious to see what CEL codes you have.

 

OK, so the OBDII adapter I ordered did not work so I sent it back. It would connect to Bluetooth, but not read the protocol no matter what I tried so I will order the more expensive one that was suggested. I want to order everything at once so also ordering the 5" deck plate, spark plugs, K&N air filter, 16oz fuel additive Seafoam, fuel filter and oil filter (what brands or part numbers on rockauto??), replacement tailgate cables (one is broken),

Additional questions:
You mentioned Seafoam through intake as well. Is that a different Seafoam product?
I'm assuming that the transmission fluid stick is the red one with a lock on it. If this is the case, it is very slightly browned and smells like almost a sweet metal...not really burnt. Should I replace anyway and add transmission fluid to my list?
Can you provide a good article on performing your recommended maintenance on the Differential(s) <- Still not exactly sure what these are or if I have more than one.
With the PCV valve, what am I looking for to determine if it is in need of cleaning or replacement? What would I clean it with?

Some more info about my truck: automatic, 2WD, TRD, came with a metal camper shell, I added green coolant to what appeared to be green coolant

Also, forgive me. I am 20, this is my first self-bought truck, my dad/uncles know little about cars' internals, and I only have a couple friends that do so assume all of this is new to me. I'm on an extremely low income but I'm a big DIY guy, and I have a feeling doing all of this is a good start to begin filling in the knowledge hole that revolves around cars for me.
Thanks guys

 

when working on the engine or replacing engine parts, it's best to stick with OEM as no one around the forums seems to have good results with anything else.

As far as seafoam goes, it's not really worth the money IMO. I have used it before and used to swear by it, but some more knowledgable people have said that its just snake oil. If you want to clean out your fuel system, Chevron Techron concentrate seems to be the most recommended with very good results. Depending on your mileage, you could try water decarbonization through the PCV valve to clean the top end of your cylinders. Look it up if you want to do that.

As far as your O2 sensors are concerned, you seemed to have cleared some errors which is good. However, replacing the fuel/air sensor may also do you some good. You should be able to get Denso brand sensors from local auto stores. I got mine at Advance. Good luck OP.