Really Bad Gas Mileage: O2 Sensor?

N

NViejeP

New member
I posted a topic on this a few months back and was not really able to get a steady/good answer.

Basically, I drive a 2000 SR5 and ever since I've bought it, its been getting 11 MPG or less. And its been getting gradually worse. I calculated this by filling up the gas tank till the pump stopped, recording how many miles I drive by the odometer, and than filing up to the top again.

I drive basically only city miles. I stop at a lot of red lights, stop at lots of stop signs, and seldom go on the highway. I get like 11-9 mpg driving all city.

So basically, I'm getting terrible gas mileage. I've had so many mixed opinions, I don't know what I think. Some people have said that its completely normal for such a big car, and some people have said that it's not normal.

I have been suspicious that its been the oxygen sensor gone bad, I'm at like 75,000 miles right now.

Can I get some feedback? Normal or not normal? Change the O2 sensor or not?
 
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Is your check engine light on? When's the last time you gave her a tune up (plugs, wires, ect.) and checked the ignition timing? Is it running rich? You could smell unburned gas coming out the exhaust if it runs rich. Give us a bit more on the way the truck runs and double check the engine tuning. You could also have something wrong with the drivetrain like something rubbing or a bad wheel bearing or who knows what else. Tell us more!
 
TheBlueWave said:
Is your check engine light on? When's the last time you gave her a tune up (plugs, wires, ect.) and checked the ignition timing? Is it running rich? You could smell unburned gas coming out the exhaust if it runs rich. Give us a bit more on the way the truck runs and double check the engine tuning. You could also have something wrong with the drivetrain like something rubbing or a bad wheel bearing or who knows what else. Tell us more!
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My check engine light is not on. I gave her a tuneup about 3,000 miles ago. They checked everything and did all the basic tuneup things. I don't really notice unburned gas, maybe if I try to smell it tommorow, i'll pick it up.

I've got bigger tires than usual, (31x10.5 to be specific) but there's no rubbing or anything. I realize that the odometer may be off by a little bit, but from what I hear, its very minimal.

I havne't really had any problems driving her, my only complaint is that it gets terrible gas mileage.

I drive mainly city, and I never get more than 150 on a tank. It all adds up to less than 10 MPG. Of course this number goes up on the highway, but it still seems low to me.
 
So I called in the dealer, and he seemed pretty confused, but he did mention that the mileage I was getting seemed pretty normal. Any opinions?
 
I drive a lifted 2004 with larger tires than stock and a V8. Around town I get an average of 15 MPG and on the highway I get about 18. Something sounds goofy. The only time I ever get near 10MPG is if I'm towing my 2500 LB trailer in the mountains.:confused: :confused:
 
i avg 14/15mpg...idk..mayb everyone else does alot of highway miles, i do alot of city driving..but meh i love the truck..savin some cash for a nice couple of days at the mechanic of some precautionary maintnence....
 
So when you guys get like 15 MPG city? Thats still a hell of a lot better than 9-10 mpg. What do you guys think? O2 sensor? any help?
 
I noticed that your location says san frans....i visited your lovely city last summer.....and the food ...woow....anyway. I also noticed how steap your roads were around downtown as I was walking to site see... you think the road condition is play a role.. also emission on cali vehicle should be over par...meaning that in most cases if something was really wrong ...your check engine light would go on with a rich condition code..
 
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I really don't know what could cause that large a difference. I would seriously have to be driving with my foot to the floor to drop the milage to that level. Maybe O2 sensor but i would think you would be throwing check engine error codes if they were that far off.

Sorry, I can't help. I haven't seen this before.:confused:
 
Tucson T4R said:
I really don't know what could cause that large a difference. I would seriously have to be driving with my foot to the floor to drop the milage to that level. Maybe O2 sensor but i would think you would be throwing check engine error codes if they were that far off.

Sorry, I can't help. I haven't seen this before.:confused:
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:iagree:

The hills may have something to do with this, but the town I went to college in (Duluth, MN) has very steep and long hills and I never got milage that bad in any vehicle I drove there, including my friend's out of tune 2000 Explorer. Even during the extreme wind and cold of winter combined with the hills didn't yield milage that bad. You said it was at the mechanic so even if your check engine light didn't work (it comes on for a few seconds when you start it, right?) the mechanic would have found the codes. Check the engine control system (computer). I'm all out of other ideas for ya, sorry, that really sucks. So Gay
 
If you are willing to spend the money and haven't come up with any other solutions, find a local Dynojet and do a dyno run with Air/Fuel ratio.

If your engine truly is out of tune, you should see some problems there in both HP and Air/Fuel ratio.

The other thing to do is go ahead and replace all the O2 or Air/Fuel ratio sensors. They do degrade over time even without triggering the CEL, and with new ones you should see at least a small improvement in mileage and driveability.

Beyond that, I think that hilly SF probably has a lot to do with your poor mileage. Short trips with a cold engine and lots of frequent braking will really do you in. I'll bet a hybrid vehicle with regenerative braking would be just the ticket....
 
Hum.. I see.

Well I mainly use my car to drive to school and back. And yes it is hilly. And I do stop a lot of stop signs and red lights.

I don't really drive slow, but at the same time i'm not really ramming the pedal.

The CEL does not ever come on, I havne't seen it on since I bought the car.

I reall don't know what to do. I have people telling me that its normal, and other people tleling me its not.
 
I dont think you are calculating it correctly -as you are now driving a different size tire -your tires most likely need less revolutions to equal a mile. your odometer is off -more than you think.

Im wiling to bet if you put the stock tires back your mileage will go back.
 
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NViejeP said:
Really? From my understanding, the change is neglible. Anyone else have an opinion?
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Measure how much extra diameter your new tire/wheel comination is. Then figure out the distance travelled by one revolution of the combo, and then compare that to your old setup and see the % difference. I can help you with the math if you need it, PM me.
 
Right now I've got 31x10.5x15 tires.

My old stock tires are 225/75/15

The tire size calculator doens't have an option for 31 x 10.5 tires.

What hsould I do?

thanks for the help by the way, appreciate it.
 
According to the tire size calculator posted above, your stock tires at 225/75R15 is 28.3" overall diameter. Without knowing what brand your new tires are, I got 30.7" overall diameter according BFG's data for their 31x10.5R15/C All-Terrain T/A KO tires.
 
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