My dealer said there are three of these sensors,found and replaced two so far, is the 3rd one close to exhaust manifold? (oxygen-sensor)

 

From your other posts, I see that you have a '95.

I can only see 2... One in front of the catalytic converter and one behind it. Follow your exhaust from the manifolds back to the catalytic converter. You should find one O2 sensor between the manifolds and the catalytic converter. It should be located between the 'Y' in the y-pipe and the cat. Then you should have one O2 sensor after the cat.

 

From your other posts, I see that you have a '95.
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Crap, how stupid to forget to state such obvious info,sorry about that!!

I thought 2 sensorsmaximum myself(exactly where you said)& afterputtingthem in,they say there are 3 .Having no shop/light, i'll have to wait for daylight to see/get grimmy down there. I still cannot believe i'm battling this up,down idle loping/RPM jumping/acceleration issue. It's really the worst at intersections wherefor no reason, it'll just lurch forward, trying to accelerate as if there was throttle being applied,then just as quickly stop,run great for 2minutes then "ha gotcha again sucker".. this is soo nausiating Especially AFTER taking it to the shop.. yet AGAIN for a diagnosis againyesterday & putting it on the crap code reader charging the handsome$106-sensor & diagnosis-$85. Still no fix

 

Well i looked high an low for this mysterious3rd sensor..can you for sure confirm it doesn't exist Swartllk?

[IMG]local://upfiles/5428/E3D41ED3EE744A3280525842A3B627E3.jpg[/IMG]

 

I am fairly confident in stating that you only have 2. The one before the cat is the only on that is used for fuel delivery. The one after the cat is for emissions monitoring only.

 

Correction: Swartlkk!

Also should point out #10 is supposed to be the 3rd sensor.

 

#10 on that list is the upstream sensor in my references... Which would make that sensor #1.

Have you looked under your truck? If you follow the exhaust from the manifolds on the engine back, you should be able to count the O2 sensors that are there.

When I just looked up the AC Delco part, it does make reference to 3 sensors, all identical. Funny that my other reference (alldata) doesn't show the upstream sensor if that is in fact how it is laid out. Anyway, if that is the case, then there would be one sensor IMMEDIATELY after the 'Y' in the y-pipe. Then there would be one directly ahead of the cat and one directly behind the cat. But again, my references seem to be misleading. Without a truck to look under, I guess I can't answer for sure. But you should be able to find them all...

*EDIT* - I'm almost wondering if there was a mid year change...

Here is the illustration from my alldata reference file:

 

I was told my 1995 only had two also. One pre and one post cat. My 95 is a late 95 (May of 1995).

 

I got in there good. I completely closed my hand around the entire exhaust pipe, after the Cat sensor as to make sure it wasn't hiding up top somehow, then slid my hand to,and past the y-connector & right up to the manifold. Then looked really good around sprk plugs,hoses..i think this is a big pile of poop this 3rd one.

 

I'm betting that early '95 had 3 sensors while sometime mid model year they consolidated to 2. Funny thing is that in '96 & '97, they had 4 O2 sensors and then consolidated down to 3 from '98+.