Wanted to get some ideas as to what may be causing a recent drop in my overall gas mileage. I have not changed my basic driving habits ( no hard acceleration, jack rabbit starts etc). I can see no difference in overall operation or performance. There is no indication of an issue, no CEL indications nothing out of the ordinary, but my milage has gone from around 300-340 miles to a tank to around 225-240 a tank. Could one or both O2 sensors cause this? Any other things I should be looking at or checking for adjustment/replacement? Thanks for the inputs!

 

Did it suddenly get very cold?

That's a pretty big drop. I'd check plugs/wires first. Others might have more suggestions. Consider this a bump

 

Could be your O2 sensor?

 

Winter here in the northwest has been anywhere from low 30's to upper 40's but nothing really unusal. Some rain/snow at lower elevations (where I live) will give the plug wires a go over. Thanks for the thoughts.

 

Thats what I was thinking too, but is there anyway to check, test or determine if or which of the two O2 sensors could be contributing to the issue?

 

Depending on your regional EPA regs, this is the time of year (March 1 here) when refiners switch to Summer blend fuels that are reported (by me and others) to increase fuel consumption by about 10%.

That doesn't explain your 33% drop fully, but it's a start. I'd check the obvious first like tire pressures and air filter, then go to the harder, more expensive stuff like plugs. O2 sensor maybe, but wouldn't that throw a code?

 

I'm in the same boat- I'm attributing it to winter fuel+other cause. The Plugs and Wires are due- overdue- and I was hoping a MAF/throttle body cleaning would fix the low mileage when my day off+nice day arrives. I've been considering Seafoam too. (would have to do that BEFORE the plug/wire swap though...) I've been loathing the thoughts of an O2 sensor problem...

 

Maybe you suddenly got better at math? You don't mention what's a tank either. 15-16 gallon fill up?

Consistently getting 300-340 miles out of 15-16 gallons is kind of far fetched to begin with.

 

o2 sensor can easily do this...send signals to make ecu think it's lean and end up dumping more gas in

have exhaust gas analysed... that will answer a dozen questions right there

 

It's a Washington State thing... Senate Bill 6508 (http://apps.leg.wa.gov/documents/bil.../6508-S.SL.pdf), all gas stations to have a 10% ethanol blend, but it can be as high as 20% (even though the pump is labled as 10%). Your gas station probably just switched over.

We can thank the corn lobby and the uneducated greeners who think that the blend is reducing emissions.

If you change your thread title to Washington State Drop In Gas Milage, I bet tons of people are experiencing the same thing (I know I am).

Write your state senator and representative (http://apps.leg.wa.gov/districtfinder/), I already have... there was a bill to provide at least one pump with non-ethanol gas (for marine and avaiton use - ethanol does bad things to fiberglass, and it's a safety issue in aircraft), but Washington state is a feel-good-go-green-say-wa state so the bill was swiftly killed.

 

i got 250 miles on a good tank. testing O2 sensor are very easy with a multimeter, find a service manual and get the specs based on your vehicle. i don't know if there's california emission or no on your year 4runner.

 

oh, that blows. i watched a TV program just last week on the this issue, it said most gasoline cars' fuel system are not designed for ethanol specially the seals. it will cause premature leakage for sure. basically all the rubber based seals need to be replaced with nylon based material to prevent this.

 

Well lets see,
15 gallons, 300 miles is 20 mpg
15 gallons, 350 miles is 23.3 mpg

15 gallons, 225 miles is 15 mpg
15 gallons, 250 miles is 16.6 mpg

So how is this far fetched as you said to get 23 mpg?
On my trip to California just this past July, driving I-5 @58 miles per hour using cruise control, not romping it, power passing, running 70mph just because you can legally, I got anywhere from 21-24. Around town here at home, I normally get 18-20. I was consistantly going 300 miles on 15-15.3 gallons in town driving,(20.00-19.6078 mpg) so I did the math ... when I fill the tank, I fill the tank. I normally will not let the tank get too far below 1/4, don't like to see that little gas pump light come on.

 

Good tip, will have to check that out, thanks BBM

 

I have the FSM for my 98 so I will need to look that up, would be easy to I'm sure as I know how to use DMM. Washington state vehicle, not Calif emissions (thank God for small favors) thank you

 

Please post how the testing goes.

More on my ethanol tirade - Ethanol doesn't store well either (absorbs water), after it was in my motorcycle for 4-months I could no longer get my bike to idle. I went to the local airfield and filled it up with 100LL (100 octane, low-lead, NO ETHANOL) and it now idles like a dream.

 

california emission vehicles were sold nationwide, not just within california. why i ask? because on a ca spec 4Runner, the first bank1 sensor is an Air/Fuel ratio sensor, not an "Oxygen" senor, thou they look the same. one way to find out is to call a Toyota dealer service dept. foreman, give your VIN, they can pull it out of the computer.

 

I get the same question all of the time. First check your basic... air filter, tune up, and check the air in your tires. Then see if you can get a scan tool with the O2 sensor parameters and fuel trim (not sure if Toyota goes by FT numbers though). The O2 sensor should vary when in closed loop from 20mV up to 800mV on the pre converters.

 

Sounds like a good project writeup Ritzy! Mine has gone down as well a few mpg inexplicably.

 

my mpg is down to and the check engine light was on and off for awhile and now its stuck on so while i was getting all my new parts for my tune up i got the check engine light checked and my o2 sensors are out... and i wasn't sure if on a 4runner if it mattered.. but now that i read this i think that i will fix em...

i had a 98 eclipse rs and my o2 sensors going out actually helped my gas mileage it went from 30mpg to 36mpg on the hwy...

but i guess its a totally different thing for my runner