My fuel milage woes, faulty o2 sensor?

[JDMMA70]

So i get roughly 16.2mpg ON THE FREEWAY, before anyone says boost leaks, checked em ZERO. Now i have zero codes as well, car runs smooth and great just gets shitty milage. I am auto as well but even i know it shouldnt be THAT bad. Now i know my car runs rich occasionally when on the highway and i boost a little to pass a car as soon i let off i get a nice pop out the exhaust. This pop is coupled along with black smoke. I also get a little black smoke under boost, a friend who was following me pointed it out. Now im hoping the problem is something stupid simple like a o2 sensor as mine is the original that came on the car. However i also wonder if its because the engine has a upgraded turbo on stock fuel, but i dont think that should be an issue since the stock ecu should be correcting it. I was told the 20G is the largest turbo the stock TCCS can handle.

Id like some insight please.

Tire pressue is correct, as is the alignment.

Thanks for reading.

 

[Nick M]

A lazy oxygen sensor can cause poor fuel milage. And not much else.

Long term fuel trim also effects milage.

 

[SrBigbutt]

I've been thinking the same thing about mine. Since I did my HG and 57Trim turbo I get like 14-15mpg. I drive mostly city though.

 

[Supra-Man18]

pfft i get about 10 miles per gallon.. : /

 

[supraguy@aol]

I don't really see why turbo size would affect mileage so much. I presume that
The TCCS is simply trying to keep a set stoichiometry during closed loop cruise.
How are you controlling fuel? Do you have an SAFC? AFPR? Lexus AFM?

 

[Nick M]

I don't really see why turbo size would affect mileage so much.

It doesn't. What does is the volume of air through the air flow meter and engine speed. A bigger turbo when pushed does get worse milage than a stock turbo, as the turbo is moving more air through the engine.

 

[JDMMA70]

As I stated in my first post stock fuel, stock everything, my only gripe is I get 16.2mpg cruising on the freeway. Im hoping my new oem o2 sensor fixes the problem, once I install it.

 

[Zumtizzle]

Test The O2.... theres a procedure in the TSRM.

 

[JDMMA70]

I can't test it per tsrm since the plug was cut off. Its hardwired in right now. The plug will go back on with the new o2 sensor.

 

[jetjock]

Yeah, just get a new one. Much cheaper than a pin through the insulation or using the Ox terminal in the diag block....

 

[IJ.]

Yeah, just get a new one. Much cheaper than a pin through the insulation or using the Ox terminal in the diag block....

 

[Nick M]

I can't test it per tsrm since the plug was cut off. Its hardwired in right now. The plug will go back on with the new o2 sensor.

You can check it in the diagnostic box. You can also look at long term fuel trim while there, what Toyota calls Vf.

pfft i get about 10 miles per gallon.. : /

So does my Yukon.

 

[JDMMA70]

Mods are lively today aren't they?

Anyways, i already talked to zumtizzle in flashchat a few hours ago about testing it through the diagnostic box, and i already plan on testing it.

And yes jetjock since i already ordered it a few days ago, it doesnt matter much now does it? My mistake for not checking before i bought it but at least ill have a new one in place.

 

[jetjock]

Will it matter if it's not at fault? Based on the fuel economy figure mentioned you have other problems. Then there's the lack of O2 codes but hey, at least the folks you bought a new one from are happy

 

[JDMMA70]

Will it matter? A little but i have some piece of mind i have a new o2 sensor. Now this thread was to help narrow it down to other possibilities. Of course im going to test the o2 sensor, however i did ask for opinions on what else could be the problem. So do you have some insight you'd like to share (not trying to be an ass but that is a legitimate question)?

 

[jetjock]

I just don't agree with throwing parts at a problem.

O2 sensors are the most needlessly changed parts on cars. Pretty sad when one considers how easily tested they are, at least for use on OBDI vehicles. That said, without going into detail about what the TCCS does when open loop, a dead sensor should not cause fuel economy to suffer to that extent unless there are other problems. I say should because it's possible but unlikely.

You can also check the sensor off the car using a propane torch. Look in my old SME section for the procedure. Kind of moot now though because you went and bought another. Since troubleshooting this symptom should have started by checking the loop anyway you're back to square one. You simply arrived there the most expensive way. Try it, let us know, and we'll go from there.

Keep in mind *accurate* fuel economy can be difficult to ascertain. Everything I'm telling you is predicated on your claim of 16 mpg. You didn't say how you arrived at that or even what your typical mileage is. It matters because say, if your mileage is higher the problem could be the O2 sensor alone. The point is we're trusting the figure you supplied to be accurate. If it's not we're pissin' in the wind...

 

[supraman7mgte]

Bad plugs? Dirty air filter?

 

[JDMMA70]

Bad plugs? Dirty air filter?

neither of those.

 

[jetjock]

On the EFI engine a dirty air filter will not effect fuel economy, only power.

 

[supraguy@aol]

dragging brakes? Bad(really bad) alignment?