How do I change the Oxygen Sensor? /94 3.4L v6...

[sad-lumina-owner]

I have got an O-sensor ($70) and have looked at the underside.

The exhaust pipe runs up the center at the engine, and the O-sensor appears to be mounted on top of the pipe/manifold just behind the engine.

It seems completely inaccessable.

Do I have to drop the whole f*** motor out just to swap out the sensor?

Has anyone done this? I would like to swap the O-sensor because I think it may be causing the car to burn too rich. Any comments?

I know it needs a new Cat Converter too but this can wait until E-test time (next year).

This /94 car is OBD-I so it has only one sensor before the cat-converter, and no sensors after that.

[Schrade]

Yup - a broken O2 will cause open loop fuel delivery, which is max fuel, further fouling of cat convertor also.

You probably will have to pull the exhaust pipe into which the O2 is screwed. I just did this recently on another car, and it is not an easy task.

Are you sure your O2 is bad? Did you test the circuit for proper voltage? Proper ground?

[sad-lumina-owner]

Originally Posted by cbec1999

Yup - a broken O2 will cause open loop fuel delivery, which is max fuel, further fouling of cat convertor also.

You probably will have to pull the exhaust pipe into which the O2 is screwed. I just did this recently on another car, and it is not an easy task.

Are you sure your O2 is bad? Did you test the circuit for proper voltage? Proper ground?

It appears to be as difficult to reach the O2 sensor/wires for testing as it is to replace it.

As near as I can tell, the O2 sensor is on top of a part of the exhaust manifold pipe coming out the back of the manifold and very close to the engine block, perhaps about as high as 'mid-engine'.

To change the spark plugs on the backside of this engine normally requires you detach the engine from its mounts and lift/tilt it forward (or back?).

I got around this assininity by sawing holes in the firewall/engine compartment body, so that I could get a socket wrench on the back 3 plugs.

This obviously won't work for the O2 sensor. I think once again I'm supposed to actually disconnect the engine mounts and lift the engine in order to get at the 02 sensor. What Aholes the GM designers were here.

I guess I'm going to have to learn how to pry up the motor without doing too much damage, to get my hand in behind the engine from the top.

Any experiences/suggestions are appreciated.

[Schrade]

Originally Posted by sad-lumina-owner

It appears to be as difficult to reach the O2 sensor/wires for testing as it is to replace it.

As near as I can tell, the O2 sensor is on top of a part of the exhaust manifold pipe coming out the back of the manifold and very close to the engine block, perhaps about as high as 'mid-engine'.

To change the spark plugs on the backside of this engine normally requires you detach the engine from its mounts and lift/tilt it forward (or back?).

I got around this assininity by sawing holes in the firewall/engine compartment body, so that I could get a socket wrench on the back 3 plugs.

This obviously won't work for the O2 sensor. I think once again I'm supposed to actually disconnect the engine mounts and lift the engine in order to get at the 02 sensor. What Aholes the GM designers were here.

I guess I'm going to have to learn how to pry up the motor without doing too much damage, to get my hand in behind the engine from the top.

Any experiences/suggestions are appreciated.

Yikes!!! What a stinker! Yup - you can figger out pretty quick, that the guys who design them ain't the ones who gotta' get a wrench-on.

Still seems the best way is to pull the exhaust, and the cat, since it's got fouling too, and while you're at it, you can feel around in the cat with a BIG LONG screwdriver, and ream around in it real good and see if it's all in there tight, until it's all loose and falling out.

Just make sure to not ream around in it more than 30 minutes or so and let it all fall out, since it's illegal to spend too much time reamin' around in it and improve gas mileage by doin' so

[helmdoggie]

I had this done this spring. I bought the o2 sensor and looked underneath and there was no way. I called around and Midas quoted me 2 hours labor and they would use my part but not guarentee it which was fine. I went in to check on it after about four hours and talked to the guy that was doing it. He acutally let me come out and look at it. You have to take the exhaust off. He took a torch to a open end wrench and bent it to get to it. He actually had good access after he did this but he was having trouble breaking it loose. When I got there he was getting ready to call his tool guy to see if he had anything to help and low and behold they make an o2 wrench just for that o2. I'm pretty sure it was MAC tools, but what it's called I don't know. You may just want to call around and see peoples price to replace it with your part. I actually found a coupon for 25.00 off so my total price was about $100.00. It only calls for 2 hours of labor in whatever book they use for quotes. It took this guy around 8 hours he said. I have a 96 3.4L. My guess is this job is next to impossible to do laying on your back in your driveway. (Thats where I do my work.) You need to get the car up so you can put some umph into it to break the o2 sensor loose. Hope this helps. Good luck.

[sad-lumina-owner]

Originally Posted by helmdoggie

I had this done this spring. I bought the o2 sensor and looked underneath and there was no way. I called around and Midas quoted me 2 hours labor and they would use my part but not guarentee it which was fine. I went in to check on it after about four hours and talked to the guy that was doing it. He acutally let me come out and look at it. You have to take the exhaust off. He took a torch to a open end wrench and bent it to get to it. He actually had good access after he did this but he was having trouble breaking it loose. When I got there he was getting ready to call his tool guy to see if he had anything to help and low and behold they make an o2 wrench just for that o2. I'm pretty sure it was MAC tools, but what it's called I don't know. You may just want to call around and see peoples price to replace it with your part. I actually found a coupon for 25.00 off so my total price was about $100.00. It only calls for 2 hours of labor in whatever book they use for quotes. It took this guy around 8 hours he said. I have a 96 3.4L. My guess is this job is next to impossible to do laying on your back in your driveway. (Thats where I do my work.) You need to get the car up so you can put some umph into it to break the o2 sensor loose. Hope this helps. Good luck.

Wow this story just seems to get worse. Special tool? I've heard this before with other things, like front calipers etc.

Some cars are lemons. This car was DESIGNED to be a prick in the ass.

Meanwhile, I was thinking about the fact that the O2 sensor has a heater built into it, which is on when the key is on.

They used to say DON'T leave your key on, because you'll burn out the points on your distributer. That was in the days of carburetors.

Since this is fuel injection, (it has no mechanical 'points') I figured that it should do no real harm to leave the key on (other than drain battery).

So I have started turning the key on in the morning for about 40 seconds before starting the car. (the O2 sensor has to be at about 600 degrees before it works properly).

Incredibly, now the car seems to start properly in the morning as though it was already warmed up! (I haven't tested this in 20 below zero weather yet).

The O2 sensor may have some life in it after all. Perhaps not letting the car go into "open loop" mode on cold mornings will prevent plugs and cat converter from fouling.

Now all I need probably do is find a way to clear out whatever soot and crap has built up in both the O2 sensor and Cat Converter.

Isn't there some product(s) that will clear out soot and/or burn off deposits? Maybe I don't have to change the 02 sensor yet at all.

Maybe I can just clean it "in situ" somehow without dismantling the car.

I hope someone knows if or how I can clean out the exhaust system from previous foulings and rich idling. Any ideas?