Replace O2 sensor

[dutchjeep]

Hi All,

My mileage is not very good. Although I drive the car like a senile senior citizen, I have a hard time getting 14mpg (this is a '92 inline 6 with 4wd that I don't use much). I have used engine/injector cleaner in the fuel, replaced plugs/wires, replaced the (cracked, of course) exhaust manifold, but no changes (car sounds and runs a lot better but mileage is pretty much the same). Since I don't know when it was last replaced I thought it be a good idea to replace the O2 sensor. Couple of questions.

1) Is that a good idea?
2) Do I take it out warm or cold?
3) Do I use PB blaster to get it to come out?
4) What replacement should I buy? Just standard at autozone or are there better/worse brands?

Thanks,

Tim

[5-90]

1) Probably. The "spec" service life of a HEGO sensor is 80Kmiles - although I've seen them go more than twice that (I've still got the original unit in my 88 - nearing 250K. I should probably think about replacing that...) Since the HEGO signal is used to "trim" fuel metering, signal degradation over time would cause fuel economy issues.

2) Warm. It's easier that way, believe me!

3) If you remove it warm, you should not need anything but a HEGO sensor socket or a 7/8" wrench (six-point or flare nut - you will want to grab it fairly well...)

4) I've had good luck with ACDelco, Bosch, and Borg-Warner. I do not advocate using the "universal" models - they don't work as well (part of the compromise they make to make them work with everything.) After all, if a "universal" sensor was doable, why doesn't everyone use it to begin with, and save printing the catalgoues? I know they use different wiring connectors between manufacturers, but don't let's get too silly...

Note that you should have a coating of never-seez on the sensor threads right out of the box - if you don't, put some on there! Most that I've seen have little rubber covers over the threads - you remove that cover, note that there is never-seez on the threads, and install.

5-90

[Idiot Wind]

1. Yes however you may have more than 1. I thought most had 2 and some of the California rigs had 4 due to stricter emissions standards?

2. I took mine out cold. However mine wasn't as old as yours and though they looked rusted on there good, they came out rather easily.

3. Not sure why you couldn't squirt a little on there. I probably did.

4. I replaced mine with Bosch sensors from Autozone. Not aware of any that are really better/worse. I do believe when I changed mine out there was a Universal sensor that required a little splicing to work or a plug and play type. I paid the extra bucks to plug and play. (it wasn't much more).

You can also get some good info by using the search feature, you will get plenty of info. Probably better than what I gave you.

*edit* I got beat to the punch. when in doubt, go with 5-90 :)

[dutchjeep]

Thanks 5-90 & Idiot Wind, great input! Will not go for universal, but get a Bosch or something. WIll try warm without the blaster, if doesn't work.....well it's never too late to get the blaster out, right:)?

Idiot W., I think you're right about more O2 sensors. This one sticks into the pipe right after the manifold connects to the main pipe. I believe there is at least one more but that's just a check on the cat (I think).

Tim

[5-90]

Correct. The "downstream" sensor (after the cat) was introduced in later OBD-I vehicles in CA as a "check" on the cat. However, that one doesn't have anything to do with trimming fuel delivery, so it's likely not the problem.

Also, later OBD-II XJ's w/AMC242 have a total of four HEGO sensors - the exhaust header is split in half (with each half have a sensor, and then going into a "pre-cat,") and there is a sensor after each "pre-cat."

Considering you have a 1992, I'd be mildly surprised if you actually have two HEGO sensors - but I don't have my FSM handy (packed for an aborted move. Should have it out next week, I think...)

5-90

[dutchjeep]

I don't know about those other O2 sensors on mine either. I don't have a FSM (would love to have one though, where is a good place to get them?). In fact, I didn't know the first one existed either until when I was replacing the exhaust manifold I found someting coming out of the pipe sticking in my face with some wires coming out that were anoyingly in the way of me tightening the manifold to the pipe. I was intrigued enough to check on what that might be doing there and tata...an O2 sensor.

Tim

[5-90]

If you have a "downstream" HEGO sensor, it is either screwed into the tailend of the cat proper, or in a bung in the pipe right after it. Since you've seen one, you now know what they look like...

Chances are, the downstream HEGO (if present) will be screwed into the topside of the cat or the pipe after it, so feel around or use a mirror.

If you have to get a pipe replaced, the HEGO sensor uses a standard (metric) thread - M18x1.5, I believe. Most any exhaust shop should have bungs for that in stock, and they just drill a hole and weld the bung in.

5-90

[niko3257]

just did my O2's like 3 weeks ago. i noticed a 2mpg increase. could be more but i'm a little heavy on the pedal. i changed all 4 of them.
just be careful they get a little expensive.
also use PB blaster. soke them up really good before you start.

[dutchjeep]

One more question. I was gonna buy that O2 sensor this weekend but then I realized I probably should check the engine codes whether it was bad or not. So I did but didn't get an O2 reading, just a 12 - 55 (battery disconnected and end codes). There was also a 62, which (by my info) has something to do with the "EMR mileage cannot be stored in EEPROM". Not sure what that means but it probably has nothing to do with the O2 sensor. So are these engine codes the thing to go by? In other words, is replacing the O2 sensor possibly still a good idea despite the fact that the codes indicate no malfunction?

Just wondering before I spend the 60-or-so bucks. Thanks, --Tim

ps. what does that 62 really mean?

[niko3257]

if you have no code for the O2
then it works.
it might not be reading as good as a new one.
and might not get you as good gas mileage as a
new one. but thats your choice to replace them.
it's fine as far as your describing.

as far as you other codes not sure.

[gregmondro]

Don't forget to put anti-sieze on the threads when you install the new one :)

[bacelaw]

is there danger of spraying PB blaster on the CAT? i mean, that thing gets pretty hot - couldn't the PB ignite??

[niko3257]

it sould be fine with pb blaster.
i used it on all 4 of mine.
just do it when the care is cold.
and whip off when done.
then start and let it all burn off.