Originally Posted by midiwall

Nope, driving at less than WOT (Wide Open Throttle) is _ALL_ about the front O2 sensor. This is how it works...

When you're generally cruising around town, the ECU (computer) is in "Closed Loop" mode. This means that the ECU is using the front O2 sensor to make a lot of it's decisions on how much fuel to dump into the engine. In Closed Loop, the ECU will do what it can to get the engine to run at a air-to-fuel ratio ("A/FR") of 14.7:1. This is called Stoichiometric Conditions, and is the optimum ration of air/fuel for complete combustion (but fwiw, not optimum power).

When you slam the pedal to the floor, the ECU kicks into "Open Loop" mode and basically ignores the front O2 sensor in terms of worrying about fuel delivery.

Okay, back to closed loop...

The O2 sensor will read each "puff" of exhaust as it comes by, and it reacts pretty quickly. By the normal nature of these engines, the cylinders really don't run the same fuel mixture, and as such, the O2 sensor will read a different A/FR for each exhaust cycle. That causes the ECU to see a varying number, and as a result, it will react constantly and adjust the amount of fuel based on the last O2 reading. If you were to watch this with a A/FR meter, you'd see it swing pretty widely.. mine runs from about 11:1 (lean) - 16:1 (rich). The best that the ECU can do is to react along with the O2 sensor and try to hit a value that will place the engine at 14.7:1 on average.

Now... if the front O2 sensor is clogged, "tired", old, etc. then it will be slow in reacting to the changing A/FR, or not react with it's full swing of voltages. If that happens, then the ECU will tend to push the engine to run rich, and over the course of a tank, that causes pretty poor gas mileage.


In short... The O2 sensor is often skipped over when trying to fix poor gas mileage.

Originally Posted by gwhayduke

Or better yet...Anyone have a part number off a 2nd gen front O2 sensor so we can check to see if Gadget does have a replacement? Just checked mine out and it ain't workin' correctly according to the manual.

Originally Posted by tomrunner

My 1995 SR5 12mm O2 sensor braket nuts...

I took my front 02 sensor off a few days ago without anything but alittle leverage as they weren't rusted up too bad.

After removing from the exhaust I cleaned it out with some solvents with quite a bit of junk come out of it..... I just filled up with gas today and will report back if I see an obvious increase in MPG.

I dind't feel like buying a new one since they're fairly pricey so I thought why not experiment with cleaning it first to see if that does anything...

Tom

Originally Posted by tomrunner

*********I actually have a 1996 with 12mm 02 sensor bolts*********
not a 2ND generation 1995!

Sorry for the typo in my previous message/quote...

Anyways

I first used denatured alchohol and then Acetone after the alhohol didn't remove very much junk. I filled a very small cup up and let the solvent soak into the holes of the sensor, then used and old tooth brush to remove as much junk as possible. After the first few steps my final was to put fresh solvent in the cup and resoak the sensor remove any remaining junk.

I don't much about the componets/structure of an 02 sensor but maybe I was able to clean the majority of the buildup giving an increase in MPG.
My Factory sensor had 102K miles before cleaning...

I will report later this week with my results!

Tom

Originally Posted by tomrunner

I have increased fuel economy from an absolute maximum MPG of 15.9 to 17.6.