I recently replaced my oxygen sensor because I got a code 21. The code went away but my fuel economy dropped to 15 and 16 mpg. I unplugged it and drove with it unplugged and got 35 mpg. Does anyone know what my problem is?


1994 Toyota Pickup, 2wd, 22re, std cab, swb.

 

Dang 35mpg?!? Leave it unplugged! lol

Rob

 

Yeah it's going to stay unplugged until I figure out what my prob is.lol. I have a loss in power too though. Has anybody replaced a oxygen sensor and had similar probs?

 

What brand O2 sensor did you buy?

 

35!? Wtf! I should unplug mine! LOL

 

It was a Denso O2 sensor.

 

Something else is wrong. When the O2 sensor is unplugged the computer goes into limp mode, which means it makes guesses as what all of the components should run at given the very little info it has.

Have you pulled any codes from the computer yet?

 

35 wow! i thought when the o2 was disconnected the computer ran it rich, not lean

 

that's a good point. It would appear that your vehicle is running very lean. I would definitely stop driving it as this can be very bad for internal components.

 

It's been a while since I have been on here but I wanted to update this. I bought an aftermarket AFM which I think might have been my problem so I took the cap off and adjusted it. I now get 23-24 mpg on highway and due to my driving habits I can hit as low as 18 mpg around town still. I also installed an OEM toyota O2 sensor from the dealer which helped as well. I'm going to stay away from aftermarket emission components from now on.

 

Good point.
What did the OEM O2 sensor run you?

 

I don't know exactly it's been a while. I'm pretty sure it was like $150 or so. It wasnt cheap. The first one I bought was $50 and it gave me all kinds of probs.

 

Can anyone offer advice? I have a 94 22re motor I just put in my truck. I was test driving it and as I recall I think it was running ok. Then all of a sudden it started running rough. When I got home I noticed that I had forgotten to secure the wiring harness to the o2 sensor off the ground. The insulation to one of the wires to the o2 sensor wore away on the pavement and the wire then wore through, so I assumed it was'nt working for about 30 miles. When I got home I used a wire nut and reconnected the wire but the truck is still running rough. Like I say, I drove it about 30 miles with the o2 sensor not working when it first happened. Did this burn out the o2 sensor when it couldn't work in the loop like it's supposed to for 30 miles?

 

Probably not.

Just test the sensor circuit directly. http://personal.utulsa.edu/~nathan-b...01heatedox.pdf Your rewiring may not be quite right.