Bad Gas mileage (O2 Sensor?)

[NViejeP]

Hey guys, I've been having bad mileage. I drive mainly ALL city, and I'm getting like 10-11 mpg, and 150 to the tank.

I filled up my tire PSI to 35. So I dont think its my tires.

Someone mentioned an O2 sensor, whats the symptons for this? My Check engine light is NOT on.

I just got the car about 1500 miles ago.

Is it the O2 sensor? Is it normal?

 

[Northof49]

How many miles on the truck?

Usually a bad O2 sensor will throw the CEL on.....but not necessarily. If it has higher mileage and the original oxygen sensor, it most likely IS had, light or no light.

Between an 02 sensor and a set of plugs I would hope to see some noticeable improvment. Do whichever is cheaper first. Check the air filter while you're at it. Stuff like tire pressure is great for fine tuning mileage, but a few PSI here or there isn't dropping you 7mpg.

 

[NViejeP]

My air filter is clean, I check it often.

Truck is at 69500. I bought it at 68000.

I drive ALL city. So I dont know.

 

[Northof49]

You're not measuring it by the gas guage per chance? Because the guages in those years have problems....some will show empty when you still have a pile of fuel left. Disregard that if you're measuring it with pump volume.

Anyways, 150 miles to a tank sucks. I have the same V6/gas tank in my Tacoma and I'm getting EASILY 250+miles 90% city, in the mountains, with a 600 pound snowmobile permenently in the back. So there's gotta be some room for improvment on your rig.....provided you're not measuring with the guage.

 

[NViejeP]

Its consistent, I usually fill up, dirve like 150 miles or so, and then I pump up, dont top off. And with however many gallons I fill up, I do

150 (or whatever miles) divided by however many gallons I fill up

totally to like 10-11 miles per gallon.

Note that I have a 2000 T4R. Our tank is like 18 or 17 or something like that. Don't know how big yours is.

 

[greasefingers]

The output of this sensor is a sinewave. It changes from 0.1 to 0.9 rapidly. So the ECU looks for an average value something like 0.45 volts. If the sensor drifts then the ECU will constantly record a lean or rich mixture. This is where no code is thrown. If it stops working then it always throws a code.

You can look at the O2 sensor as a fine tuning device for the air-to-fuel ratio. It is one factor the ECU uses to determine how long to hold the injectors open. The ECU does not use the O2 sensor input during warn-up, acceleration, or deceleration. It is only used during constant speed. This is why I call it a fine-tuning devise.

Something that would affect the air-to-fuel ratio more would be the MAF sensor. I would suggest removing it and spray it with electrical cleaner to remove the carbon from it. O2 sensor should last 100,000 miles. But it is also one of the most unreliable sensors on the vehicle. If in doubt replace the upstream O2 sensors.

 

[NViejeP]

How much would an MAF be? Could you throw me an estimate? Also an estimate for the O2 sensor?

 

[greasefingers]

Both sensors are around $ 80. (Rockauto.com) You may need two upstream O2 sensors if you have the 3.4 L v6.

So instead of shelling out $ 280 for three sensors, I would pick up a spray can of electrical cleaner from your local parts store and remove the 2 screws for the MAF to clean it first. If your vehicle also has a MAP (manafold absolute pressure) sensor then I would clean it the same way as well.

Then observe the gas mileage and take it from there.

 

[NViejeP]

Are there any tutorials to this MAF? Sounds like a good idea. I have no expeirence working with my car by the way.

 

[99t4rweos]

Greasefingers hits the nail on the head:bash: explaning how the 02 sensors work. If someone has a scanner that can display a data stream from the ECU, monitor the 02's sensors wit the eng. warmed up , during cruise and idle , the voltage should vary from just above zero to .09 of a volt. The ECU is constantly looking for changes to precisily obtain the correct air fuel ratio. If the volts do not vary, rapidly, and you don't have any thing inducing a lean condtion. I then would suspect a 02 sensor.
To clean the MAF, remove the 2 screws, take q tip with some brake or carb clean on it and gently clean the thin wire you see in the sensor.

 

[jtreibick]

Same Situation

It seems that I too am in the same situation as you. I recently bought a 2000 4runner w/ 65k miles and also get about 150 miles to the tank and average about 10 MPG based upon fillups. Is this a common problem to occur in aging 4runners?

 

[NViejeP]

Re: Same Situation

It seems that I too am in the same situation as you. I recently bought a 2000 4runner w/ 65k miles and also get about 150 miles to the tank and average about 10 MPG based upon fillups. Is this a common problem to occur in aging 4runners?

Do you drive all city? I dont know, but it could be normal. Good to find someone in the same boat as me however.

 

[NViejeP]

Also, does anyone know how much a O2 sensor cost to get replaced at the dealership or wherever? Or how much yours cost?

 

[NViejeP]

Anyone that has have a bad O2 sensor or can relate?

 

[jmtreetop]

I had a bad O2 sensor on my 98 4runner. My MPG went from 18+ to 9 MPG. The engine will run rich, hence the bad MPG. This did not throw my CEL because the O2 sensor intermittently worked. I don't remember how much it cost but the $300 range sounds familiar (dealer installed).

 

[NViejeP]

Holy $300 for an O2 sensor. Sigh.. maybe I'll ask my Dad. But this definately can explain it. I should be getting better mileage than this.

 

[NViejeP]

I had a bad O2 sensor on my 98 4runner. My MPG went from 18+ to 9 MPG. The engine will run rich, hence the bad MPG. This did not throw my CEL because the O2 sensor intermittently worked. I don't remember how much it cost but the $300 range sounds familiar (dealer installed).

Oh and on your MPG estimates, were you driving all city or mixed highway/city?

My CEL did not come on.

 

[NViejeP]

I had a bad O2 sensor on my 98 4runner. My MPG went from 18+ to 9 MPG. The engine will run rich, hence the bad MPG. This did not throw my CEL because the O2 sensor intermittently worked. I don't remember how much it cost but the $300 range sounds familiar (dealer installed).

Do you have an AIM or e-mail I can talk to you through?

 

[greasefingers]

You may be wasting time & money if you replace the O2 sensors without cleaning the MAF sensor first. Two Philips screws hold the sensor in place. Very easy to get to as well. An aerosol can of electrical cleaner (found in any local auto parts store), is all you need. Remove the sensor and spray the inside of the housing. Do not touch the wires inside the housing as they are fragile. Let it sit in the sun for several minutes and re-install it. The MAF (mass air flow sensor) has a much more dramatic affect on fuel economy then the oxygen sensor.

 

[trdtoyotaguy]

same issue here

i just bought a 2000 ltd with 82k i get about 200 out of a tank my dad with a supercharged 099 gets 260-280 what gives ?