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B1S2 O2 sensor -- 97 z-28

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R4g3fist

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Discussion starter · #1 ·
I ran a code machine on the Camaro and found that the O2 sensor at the B1S2 lead was haywire. What I need now is a quick answer to where this elusive beast is located.

Also, does this engine (5.7 V-8) have 2 pre and 2 post cat sensors, or does it have 3 pre and one post cat?

Thanks in advance :)

-Scott
 
#2 ·
provided you have decided the o2 itself is actually the problem, you would find it is the closest o2 sensor to the head on the number 1 plug side. Threaded into the exhaust. You'll need a 7/8ths wrench or if its real tight a 02 socket (reg socket won't work as the proper one has a slot for the harness to fit into)...if the 02 is real seized in there bang around the bung with an air hammer or even a punch and a hammer to loosen it up. If that car (i'm not sure) has 2 cats, you'll probably find 2 pre and 2 post
one cat would probably be 2 and 1
 
#3 ·
bank 1 is the same side of the engine as the number one cylinder
sensor 2 is the post cat sensor

you would only have 3 pre cat o2 sensors if you had 3 banks of cylinders (or someone messing with you)
so my guess is that you have 2 pre cat and either 1 or 2 post cat O2 sensors (just depends on how many cats you have)
either way my bet is that you will find the sensor under the car a few feet back from the exhaust manifolds, not the closest to the head
 
Discussion starter · #4 ·
Thanks for the input, I'm definitely sure that the O2 in question is the B1S2, only sensor with a wonky reading according to the diag.

As to there being 2 or 3 pre cat sensors, I sort of figured on a 2 and 2 set up, but who the hell knows (engineers :)).

So, this is sort of off the path, but why would a single bad reading on a post cat O2 sensor contribute (if it does at all) to hesitation during accel? The computer just not capable of making that level judgement call as to which sensor might be bad?

Thanks again,

-Scott
 
#5 ·
If the computer is saying B1S2 is bad, then it's either bad, the wiring for it is bad, or the cat is bad. Which B1S2 code is it throwing?

I don't know if a bad post-cat sensor will cause a hesitation or not--I kind of doubt it though as post-cat sensors are just there to verify that the cats are working and make you fail an OBD2 emissions test if they aren't. The "emissions-legal" street racers usually run "O2 sims" in place of the post-cat sensors to fool the PCM into thinking there are still cats installed.
 
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#6 ·
400bird said:
bank 1 is the same side of the engine as the number one cylinder
sensor 2 is the post cat sensor

you would only have 3 pre cat o2 sensors if you had 3 banks of cylinders (or someone messing with you)
so my guess is that you have 2 pre cat and either 1 or 2 post cat O2 sensors (just depends on how many cats you have)
either way my bet is that you will find the sensor under the car a few feet back from the exhaust manifolds, not the closest to the head
Click to expand...
ya, i meant the closest sensor to the head,, meaning the first one in line...also many new cars do have 3 pre cat....one in each bank, and one right before the converter...this allows much more acurate catalist effeciancy monitoring
 
#7 ·
and above is correct,,,,,downstream 02 isn't gonna cause any driveabilty issues.....as stated, it's just there to make sure the converter is working properly by comparing the level of oxygen in the exaust behind the converter to the amount in front of the converter.
 
Discussion starter · #8 ·
Well, here's the rub then --

If there are three pre cat sensors, one for each bank and one immediately pre cat, then it could cause hesitation and leaning out issues (mismatch in O2 reads in the combined exhaust, etc). If it is post cat, then yes, it would seem unlikely that the system would use it to adjust fuel into the cylinders (in my limited knowledge).

Regardless, the sensor at that location read approx 100mV constant when I cheched the data stream while all other O2's read appropriately during warm up and operation.

Anybody else here have any other ideas regarding leaning out/hesitation during accel other than MAF (reads fine, looks fine) or plugs (replaced)?


-- Re: Rodder

The code I got on a somewhat ancient code reader wasn't O2 specific, instead I went in using pathfinder 99 software and took a peek at the data stream. Two O2's at B1S1 and B2S1 read correctly (low start values, then rapid fluctuation between 100 and 1000 mV), and one O2 at B2S2 reads appropriate for a post cat O2 -- low start value creeping slowly toward 1000mV as car warms up. The aberrant reading at B1S2 bounces between 95 - 105 mV but never falls out of that range.

Thanks again all,

-Scott
 
#9 ·
well that o2 sensor is probably bad, only other possibility is the wiring, so replace the sensor and see how the hesitation problem looks

and your car has 2 pre and 2 post cat sensors not 3 pre, so dont worry about it. I believe Jeff22 is referring to new cars 2006 or newer kinda thing not a 1998
 
#10 ·
yes, i was stating that some newer cars...new than 04 to 05 is when some started....just stating that there is cars out there now with 3 pre cat oxygen sensors....sorry to get off topic.
 
Discussion starter · #11 ·
All right boys and girls, here we go again ---

Found the correct O2, replaced it, same reading however (very low, i.e. lean all the time). It also does not react the way any of the other O2's react when the car is just switched on. All others start around the bias voltage (450 mV) then work their way toward the sub 200'after about 30 seconds. This O2, prior to start, drops like a rock to the sub 50's and sits there. It also does not read at all when the car is started -- it does similar things, i.e. settling down near 80 or 90 and ticking back and forth a few mV while all others do the appropriate actions.

As far as I can tell, it has the correct bias voltage to it. I can't really do any troubleshooting on the plug, being that its sorry butt is crammed up next to the tranny pan and my fat hands can't get it out of there, but in looking at it all the prongs seemed ok. So I'm guessing wiring or ECM, with ECM being less likely b/c of the correct bias voltage. Any ideas?

Car is a 97 Z-28 with a 5.7 V-8. Hesitates almost to the point of stalling upon gentle accel from a stop, slightly rough idle (barely perceptible), and it's driving me nuts trying to fix it. All other checks seem ok -- MAF, MAP, plugs, throttle sensors, knock sensors, etc etc etc, just this one aberrant O2 that did not resolve after replacing the sensor.

Thanks again everybody, all the input has been excellent.

-Scott

PS I'm hijacking my own thread I suppose, if that's a problem I'll repost it elsewhere, just let me know :).
 
#12 ·
locate the ground trunk that the o2 sensor grounds to...possibly the ground is poor, and contributing to several failures, but only showing on the o2 sensor...if the readings on the o2 sensor are flaky, immagine what the same ground will do to the map sensor...also look at the data stream for the coolant temp sensor value...if the car is reading lean, it could be the coolant temp sensor telling the ecm that the car is very hot, and leaning it out...
 
Discussion starter · #13 ·
Hmm, I'll take some stabs at all that. As far as I could trace the wiring without tearing out the headers on or various other parts of the engine on that side, the wiring looked ok. I haven't yet found the ground trunk for the sensor(s) located on that side, but I was wondering if it would be the ECM's ground that supplied a ground to the O2.

I'll also look at the other data sets when I have a chance here.

One other quickly tossed out there thought. In the interest of science, I screwed the new O2 sensor out of the exhaust and watched what the readings did on the scanner. Once I had it free of the exhaust pipe, i got the bias reading back (450mV), and only got a different reading when I had the sensor grounded physically to the exhaust -- is that correct or aberrant?

Thanks again, I'll keep plugging until I throw the hands up in disgust and hand it over to someone with a little more pro and a little less shade tree in them :).
 
#15 ·
not sure where the sensor gets ground...i would think in the loom, as heat creates resistance, and would effect values...but the heater in the sensor would possibly get ground from the pipe...again not sure on either end...and as above posted, s2 is after the cat...make sure you got the right sensor...could unplug and look at the datastream to confirm...
 
#16 ·
Pretty much all sensors in computer controlled cars have a ground return wire that connects to the ECM ground. The O2 sensor should be the same, and I would expect their not to be continuity between any lead and ground (except perhaps a 5 or 7 wire O2 sensor)
 
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Discussion starter · #17 ·
That was my assumption as well. Ergo, grounding to the pipe is FUBAR and it's time to get someone with better gear and more than half an idea what they're doing to look at it, methinks ;).

Kustom: Aye, I popped the O2 sensor plugs to find the right one in the data stream, but replacing the funky one yielded the same problem as before.

Thanks again.

-Scott
 
Discussion starter · #19 ·
So far as I could tell, the scanner read no codes on the engine, aside from the O2 sensor (let it be known the scanner was cheap and on loan). So the misfire history was clean, but I'll admit that I didn't spend a lot of time looking at all the misfire history options.

I'll maybe take a look at the cats again, at least this gives me some ideas before I take it in somewhere, thanks all.

-Scott
 
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R4g3fist
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