Greedy

Just wondering if someone could tell me the location of the O2 Sensor on a 1999 4runner.

jimbo74

i dont know the location, but seeign as its an obd-II vehicle, i am sure that there is more than 1 sensor, you probably have a minimum of 3

Greedy

Damn. I recently have had a big drop in gas mileage and thought that cleaning the O2 sensor might help. (I also recently did the seafoam)

jimbo74

do you have a code reader? is there a cel present? have you done a tuneup recently? also what type of gas? that can majorly affect mileage as well... what kind of mileage numbers are you having? also what makes you think that you have actually had a huge drop in mileage?

Greedy

No code reader... I've always got about 230 miles per tank and after I did the seafom treatment, I am getting about 190. I pulled my plugs and they were filthy - cleaned em and my mileage improved to about 215 miles per tank. After seaching the forum I found that some people have also pulled and cleaned off their O2 sensor after seafoaming as it gets dirty from all the burnt crap that gets loosened up.

Greedy

Found It......

14thegipper

where??

pics?

MTL_4runner

No, there are only 2 and they are located in front and behind the catalytic converter.
It is usually the front one (closest to the engine) that gets dirty.

X-AWDriver

My truck is a Cali truck and I'm hoping the rear cat can be removed since I don't think the 2nd one is doing anything except robbing HP so hopefully I can remove it when I do the exhaust.

calrockx

so after the seafoam and cleaning the o2 sensors, you end up with a net loss in milage? that doesn't sound good.


also, for anyone reading this thread, here's a write up on changing the 02 sensors, also relevent if you want to just clean them. http://www.4runners.org/articles/02sensor/

calrockx

what did you use to clean them? anything in particular i should know before doing this? i think i read it just takes intake cleaner...

theryanator

Greedy

We have the exact same truck almost. I have had the same problems you have described. Except my mileage is worse than yours...do you live in a cold winter climate? Are you still getting 190 or over in the winter? I am currently getting about 180 a tank or 12.5 a gallon...terrible.

The 02 sensor was on my list of things to clean/do today with the truck...can you tell me exactly where you found it...was it eay to dis-assemble and clean? I would really appreciate your help as I have been hesitant to do this step as I have no experience working with things like that UNDER the car.

Thanks.

MTL_4runner

Here are some good documents for you on O2 sensors:
http://www.kemparts.com/TechTalk/tt07.asp
http://www.gnttype.org/techarea/ecms...O2sensors.html

This refers to a boat engine but the sensor is essentially the same (explains a bit on cleaning):
http://www.boatsetup.com/O2sensor.pdf

Here is another document on testing:
http://auto.howstuffworks.com/framed...s.com/o-21.htm

The sensor can be cleaned but I usually don't recommend it. You should do a bench test first to see if it is even the sensor at all. If you do want to clean it you can use a top end cleaner like seafoam, but I prefer to use the GM top end cleaner for this. Soak it until the tip comes out clean and then soak it in an electrical contact cleaner to be sure there is no film left on the sensor itself (the actual sensor is inside the perforated metal tube). If there is film on there when you reinstall it, you could permanently damage it and require you to buy a new one (sometimes for whatever reason the cleaning does not work either). The sensors can wear out eventually giving you a slow response so this is why I usually just suggest people get a new one instead. Be sure to bench test the sensor before you put it back in after cleaning to be sure it is still good. Again I always suggest that if you bench test it and it is bad.....just pony up the bucks and get a new OEM one.

Greedy

theryanator,

The O2 sensors are directly in front and in back of the catalytic converter on your exhaust system. If you crawl under there, follow the exhaust back from the engine untill you see a rectangular box with holes in the outer casing. It is in line with your exhaust pipe that eventually goes to your muffler. The o2 sensors are mounted directly into the exhaust pipe and have wires coming out of them. The write up in the tech section explains how to take them out.

I took mine out and cleaned them and also replaced my spark plugs but am still getting bad mileage. Truck runs great but can't get over ~13-14 MPG. I may try testing the O2 sensors as suggested above to see if they are failing. I cleaned mine with electronics parts cleaner but to no avail. As far as the climate - I live in washington state and don't beleive that we get different gas in the winter up here as it is pretty mild. Hope this helps and I will let you know if I figure it out....

MTL_4runner

Just using the electrical contact cleaner will not remove any carbon buildup.