Bad gas mileage

Hi all, I'm new to the forum.
I have a 2002 Taco sr5 preRunner 2 wheel drive 4 door quad cab. I have owned the truck 4 years. Got it with 120k miles from the original owner and she has 160k now.
I usually get about 18-20+ miles per gallon. All of a sudden I started getting poor gas mileage...10-12 miles per gallon city driving.
Changed oil and oil filter, Replaced spark plugs (dual electrode ngk), pcv valve, air filter, cleaned both air flow sensors with air flow sensor cleaner, replaced fuel filter, tire pressure is on point and always checked....I'm lost...
Help!

David

 

Maybe something wrong with the fuel injectors or ignition coils? Seems like you already addressed all the other usual suspects.

 

Yeah could be, no codes and drives sounds good and as it always did before...
This is driving me crazy!

 

Possible someone is borrowing your gas??

Pretty sure you would smell a leak.

Did you happen to put a dent in the tank??

Added larger tires or more weight in the truck??

How long has the mileage been like this now??

 

I don't think anyone is steeling my gas.
Dont think it's a leak, like you said I'd probably smell it.
Tires are the correct size, no extra weight.
No dent on tank.
Been like this for about 5 or 6 months now.

 

Did anything Change ??

Commute changed completely ??

Different gas station high speed pumps shut off faster.

Math errors??

Have you pulled any codes or is your Engine light on??

 

None! That's what bothers me most. Nothing has changed...

 

Have you driven through any water lately? Could be a cracked exhaust manifold.

Or perhaps a bad o2 sensor.


Is the check engine light on?

 

No water, im in Dallas TX its dry as can be. Were in October and it's like July here.
No check engine lights. I've had Autozone and a major shop with a much higher computer run codes to see if anything was in there...clear, nothing!

 

off the top of my head... verify that the handbrake and its mechanisms on the rear baking plates aren't stuck. the handle can be fully seated but the parking brake mechanism could still be partially "on". take a look at the throttle body for oil build up too. If so, the rings could be starting to wear... less compression/more oil consumption and less "bang" per firing cylinder. A leak down test will either confirm or deny my last suggestion.

 

When was the last time it was given a tune up?

Cleaned the MAF, IAC, throttle body?

 

If you're mpg math is correct, that is a 40-50% drop. That's huge. That's like when you get an MIL and ecu goes into safe mode and runs rich. A drop like that I don't see being a spark plug or air filter tune up thing. I could be wrong of course but I'm looking at bigger things, but it's always good to eliminate the cheaper and easier possibilities first.
When you turn the key in ign to on without starting it the MIL illuminates right? Do you have an OBD2 reader you can plug into the port and get some AF numbers? Does the truck run and accelerate the same? If so, and you verify fuel trims are good, I'm looking at physical things like someone mentioned above with the park brake and it's linkage etc.

 

You did write "no codes" but that doesn't really tell us anything. Could be that your CEL is burned out . Could be that there are stored codes that haven't (yet) reached the point that triggers the CEL.

 

I also wrote up above that I had Auto Zone read it and a bigger shop with a nicer computer read it as well....no codes

 

Kinda sorta off topic,......does the Bank 1 Sensor 2 effect gas mileage??

 

Two separate times the mileage on My 1998 v6 dropped to about 10 mpg, crappy performance too. I was thinking my o2 sensor was bad.

1. no check engine lights come on when one of my fuel injectors went bad, or was going bad. the electric component on it is what was failing. Took it to a shop for diagnosing and repair. Poor mpg and performance which went back to normal after replacing the #1 injector. I went with a new one ($50 more) instead of used. I believe the metal fuel lines feeding into the injectors needed to be removed as part of the job, it was a few years ago. The part was about $250.

2. the check engine light was on. Mileage and performance significantly improved by replacing the charcoal canister assembly. If you do that, I recommend buying the assembly which includes two vacuum switching circuits. That’s an easy swap too, take pictures so you can get the hoses connected correctly when installing the new unit. That was a little over $200 for parts.

 

NO. Sensor 2 reads how much oxygen is left in exhaust gas after cat, No oxygen GOOD KITTY! High oxygen BAD KITTY $$$.. Sensor 1 is a wide band air fuel sensor responsible for fuel trim. On your 03 that is. Earlier models had 2 O2 sensors.

 

That's a good point. A non-op or partially failing injector wouldn't necessarily throw any DTC and could affect mpg pretty heavily.
OP you could use a dowel or screwdriver to try and hear if any of the injectors sound different front the others

 

Good information! Thanks

 

I would check that each wheel is freely turning with no brake drag. Yodas are notorious for rear E brakes stuck on and front brake caliper lock.