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10,898 Posts
o2 sensor is down on the y-pipe just before the cat. If yer
looking at the front of the truck back it would be about 2:00
on the merge section of the y-pipe.

If ya get another one Ricky, if ya can't swing a Genuine GM o2
sensor, I use Robert Bosch o2's. They work real well and
run somewhere around $50.00. Make sure that the anti-
seize is covering the threads of the new o2 so if ya ever
have to replace it, it will come out easier..You'll know what I'm
talking about when you go to change the one that's in
your 89. It'll take a 7/8 wrench or an o2 socket..

Spray it REAL good with PB Blaster penatrant before you try
and take it off.

Let the Blaster work it's way into the threads for maybe an hr
or so..Believe me it will make it easier to come out..Good Luck.

10,898 Posts
Most anything will be better than the orig if you have hi-miles.
If all you can swing is 25, well that's all you can swing.

I've used Bosch and have always had excellant sevice from em.
When I was doing smogs not to long ago, that's what I would
recommend if the diag came down to the ride needing an o2.

You can alway compare a good o2 sensor with a DSO= digital
o-scope, or graphing digital volt ohm meter. You want to see
the o2 voltage go over .8 volts and below .2 volts with it
switching twice a second. This way you know the o2 is
probably ok and it's sending the correct voltages to the ECM
so it can help keep the A/F mixture at a voltage of around .45
or 450 millivolts. That's when it's been determined that the
A/F mix is around 14.7/1. Old o2 sensor can be lazy, biased
lean, biased rich, clogged up, [there's a tiny hole in the o2
to allow outside air in, so the o2 can compare outside air with
the oxy going by it's probe in the exhaust gases] and the
galvanic battery that's inside the old o2 sensor can just give out..
Not all o2 sensors have batteries, but I'm not getting into that..

I'm getting off track here. If you can only afford the lesser priced
one that's the way it is. Regardless, an o2 sensor that is
operating in such a way as the voltage is around .45 volts,
will mean your ride is running pretty good, you'll save on gas,
and your cat with last longer..

150 Posts
Which O2 sensors affect gas milage? I took my truck to Pep Boys to change Bank One Sensor 3 and a few days later the SES light came back on. I thought it was because of my transmission but it turns out Pep Boys probably changed the wrong one. I had my valve body overhauled at the dealer and they also change the O2 sensor. (at no cost to me thank God $710) The light has not come on since. I was changing my oil and noticed the #2 sensor look very clean and new. So I guess I got two for the price of one. I guess that leave the two in the headers to be changed. Does anyone change theirs as any maintenance, or only when they go bad?

10,898 Posts
Well I always had luck with good emissions if I changed out the
one o2 I have at 75,000. I find if a car or truck has been treated
with tender loving hands, you know, the maitance done on or
before it's due, the ride run easy, Chevron 89, Union 89, or
good gas like these two have been used, then you can get up
to and past 125,000 on the factory o2 sensor..I stay on mine
as far as maitance, but I do drive it HARD half the time.

So I replace the factory one with a Bosch and be done with it.
Now I only have 1. Guys whose rides have up to 3 or more, well
this can get real expensive real fast..I suppose the way to do it
is to drive your ride until a noticable lack of performace shows
up, gas mileage goes down, and the SES comes on..or do simple
testing by way of propane then a vacuum leak and a test moniter.

Course the proper way to ck o2's is with an o-scope or graphing
DVOM. These tools will tell ya how each o2 is working if you
use certain procedures. I use propane and a vacuum leak
to test the one on my ride..Works real well..

4,246 Posts
Discussion Starter · #7 ·
Man that O2 wire is a bitch to hook back up..but I fianlly got it..the cat was only $120 installed..

Man I tell ya the cap/rotor was tarshed..seems to run real good now. The test will be tommorow tho.

BTW I used the Bosch sensor, it was the cheaper one. The OEM type is what they said..

Thanx again bg's!!!!!!
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