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mysterious oxyen sensor

5K views 41 replies 4 participants last post by  TealHornet 
#1 ·
I have a 97 z28 and it has been running rich for some time. I just put in a new (second one) delco bank 1 sensor 1. I keep getting a heater circuit code but when I check the ground it has very little resistance (5ohms) and the power reads 11.65 volts. (same as the recently replaced one). voltage ranges from .2-.5 volts while running with an occasional jump to .8 volts. I have checked the injectors and they don't drip when under pressure. all temp and air sensors are within normal limits. is it possible that the sensor is working correctly (heated) but its rich enough on bank 1 to confuse the computer?
 
#2 · (Edited)
Actually, 5 ohms on a ground is a lot of resistance. So clean the grounding point up, check any connectors in the circuit for corrosion or loose fitting pins. Copper in wire could also be corroded. If heater circuit has high resistance, so could the signal circuit. There 5 ohms would totally change the reading that pcm is getting from O2.

To help you, use the wiring diagrams in 96 service manual. Get at My Files
 
#3 ·
Thank you! I retested the ground and got .1 ohms of resistance. I also tested the power from the high and low signal with the car on and got 1.51 and .87 volts respectively. voltage for the heater circuit reached 11.5 volts. oddly it through a code for bank 1 being lean... the car still smells like its running rich though. Also the engine temp on my scanner seems normal. Where would you go from here? again thank you for the help and your page is awesome
 
#5 ·
Shouldn't be any pressure on map sensor at any time. Map runs off engine vacuum, which is the opposite of pressure. Use your scanner set to test sensor data. With key on and engine not running, you should have around 5 volts on map circuit.

Crank engine and let idle. Map voltage should be in the 2 to 3 volt range. If voltage stays at around 5 volts with engine idling, map is not getting vacuum.

Your 02 on bank 1 is reading lean and your exhaust is smelling rich because pcm in response to a very lean o2 reading is adding too much gas to the mixture.

So while car is on scanner set to scan sensors look at your bank 1 o2 readings. They should be changing rapidly & going above & below the 450mv center line. Also check out your fuel trims to see how much fuel pcm is adding.

The lean condition on bank 1 can be caused by vacuum & exhaust leaks. A major problem is at the intake elbow where it goes into the throttle body.
 
#6 ·
awesome! I set the scanner to mmhg and by using your conversion on another page and that checks out normal. after clearing the codes and with engine somewhat warm the bank 2 short fuel trim read 0 and long 19 while the bank 1 short fuel trim read about 18 and long 25. I unplugged the TPS (I think making an open circuit) and the rpms jumped and make bank 1 short drop to 9. Should my next step be to buy a smoke vacuum tester and see if I have a vac leak? I cant see anything obvious ones but that doesn't mean much. the 96 service man you linked said if only one bank is living lean code it may be intake manifold or injector vac leak. Thank you
 
#7 ·
The smoke vacuum tester is a good investment that can be used on your 97 and any other car you want to test for vacuum leaks. Myself I use the old spray bottle with gas in it. I spray around areas where vacuum can leak. When leak is found, engine idle will speed up because of improved air/fuel mixture.

Be cautioned that spay method is dangerous. Have a fire extinguisher at hand if using this method to detect vacuum leaks. The smoke machine is much safer way to detect leaks.

Vacuum leaks can occur most anywhere in the many feet of vacuum tubing car has. Which is 22 years old now. The intake elbow is a trouble spot. Bad injector o-rings can leak. Even spark plugs that are loose or have defective sealing rings can leak. You will have to be Sherlock Holmes and use all your deductive powers to find the leaks.

Your fuel trims are really bad. Engines without vacuum leaks usually have trims of 0, or may be + or - 1 to 3. Your short term trim of 19 is pretty whacked.
 
#12 · (Edited)
lol as you suggested its in the elbow all the way to the bank 1 side. I have ordered a the 1LE elbow and will update as soon as it comes in! The PCV hose also seemed very loose on the crankcase side but I didn't get any smoke out it so I assume at least the valve is in check. Thank you again!
 
#14 ·
The soup is cold! after replacing the elbow the short term trims are better but still not right! it seems like the bank 1 sensor is reading better but still lean ranging form .2-.5ish. how long does it take for the long trims to follow? I drove it for about 20 minutes 2 times and they wont move past 25.

for kicks I unhooked the manifold valve on that side while running and there was some air movement through it. I also replaced the vaccum line under the elbow with no change. I suspect I have to break back out the magnifying glass again. LOL I attached some pic of my scan tool after I drove it for 20 mins. Please lmk if you see anything I may have missed. again thank you for your help!
 
#17 ·
Long term fuel trims are exactly that. They are from many short term samples. Try disconnecting the car battery. That will reset the pcm. Of course it will take some driving time for pcm to relearn.

If your fuel trims are still way off, time to get the smoke machine back out. The intake manifold can leak, as well as all the 20+ year old vacuum lines. Don't forget exhaust system from exhaust manifold to cat for leaks that cause unmetered air to be pulled into engine.

Your scan pics are inconclusive, as readings have to be seen second by second to determine proper sensor readings. For obd 1 car owners, the pc based program called "Freescan" was perfect for posting to forums. It recorded the data stream and you could play it back in real time. That way a complete picture of sensor activity could be seen.

Unfortunately, I'm not familiar enough with obd 2 scanners & programs to recommend 1 that has similar data playback capability.
 
#20 · (Edited)
Should there be vacuum in the air pump lines during normal idle with pump off? I read about a stop switch valve but was wondering if there was any acceptable amount. After plugging the intake to the pump my short and long trims started to fall. After looking at your website I also don't think I have the AIR recall/ extra vacuum control line
 
#21 ·
The valve that controls air pump flow to exhaust is built into the pump. There are check valves in the lines to prevent reverse flow or air when pump is running. Pump is electric & controlled by pcm.


Pump forces air under pressure into exhaust system and should never have vacuum. I suspect that system is not hooked up correctly if you are getting vacuum in air pump lines.
 
#22 · (Edited)
after plugging the exhaust air ports a got the short terms to go down to 0 with the long on bank 1 still stuck at 25 and on bank 2 at 10. I know there must be a small leak in the throttle body because I did see a little smoke come from there but not like the elbow. One crazy think I don't understand is sometimes the trim will jump negative. This morning when I started it up bank 1 short was at -37 for a minute with the long still at 25 then like magic will jump back up. I recorded data as I was driving and at one time the long term was down to 10 then a few frames later jumped to 25.

more on the 02 sensor
this is the 2nd sensor I've tried and is a delco. It still wont jump around like the bank 2 sensor. it just seems sluggish alternating at half the speed of the other side. ive tested the wires and I have power and ground. when started cold it almost seems like it alternates more normal and will reach up to .9 v which is when I got the -37 shtft but after the car is properly warm it slows down and will only reach up to .5

Im starting to wonder if all these exhaust fumes are getting to my head.
 
#23 ·
As long as the O2 changes readings and doesn't stay at the same mv number most of the time, it is doing it's job. The O2 that is changing more rapidly just means the pcm is having to add or subtract more fuel then the O2 that is changing readings less often.


You probably do still have a small vacuum leak. And maybe an exhaust leak to go with it.. Have you tried disconnecting the battery for a few minutes? This will reset the pcm. And after pcm relearns settings, O2 & fuel trims might be better.


Is the exhaust still smell like unburned fuel?
 
#24 · (Edited)
you prove a good point on the o2 sensor status. I have tried disconnecting the battery but will again. the exhaust does still smell like unspent fuel but less then when we started so thank you again. Do you recommend anywhere in particular to get the throttle body rebuilt? What may cause my short fuel trim to be -37 when it is cold?
 
#25 · (Edited)
I don't know anyone that rebuilds throttle bodies, or if the parts are even available to do so. Try to find a carburetor rebuilder in your area. See if they can rebuild your tb.

The only other thing would be to buy a new tb. Stay away from the larger than stock one's. You'll end up with a whole new set of air/fuel problems.

Fuel trims should be higher with engine cold. Not in the - reading. You might consider engine problems being present in addition to the vacuum/exhaust leaks. Worn piston rings allowing a lot of blow by would feed the blow by into the combustion chamber to be burnt with the fuel. Maybe that's what your smelling.

Bad valves or valves not closing all the way do to incorrect valve adjustment could be allowing unburnt gas to exit cylinders into the exhaust stream. I believe it's time for a compression check and cylinder leak down tests to be performed.

Or maybe it's time to hire a witch doctor to drive away the evil spirits residing in your car.
 
#26 · (Edited)
I hooked the smoker up to the tail pipes for about 45 mins yesterday and only got a small exhaust leak after the bank2S2. Beleive me i prayed i would find on preO2 sensor leak. lol.

I reset PCM to all trims were 0 after the smoke test and as soon as it hit closed loop it they jumped back up again. Im not sure if it was all the mineral oil in the exhaust but it smelled a whole level of terrible after that startup.

After that I one by one disconnected and plugged the vacuum at the manifold for the EVAP, PVC and line to under the TB, line to right valve cover and its inlet to the TB, line to the EGR, distributer, even brake booster with almost no change. Im not pround of this but i even put an oversized balloon over TB covering all the spring and assembly with no change. (not saying i got a perfect seal)

The fuel trims are always the worst when the car is idling. watching them as I drive down the road sometimes but only sometimes the bank1LT will even get down to 10 but as soon as I come to a stop they come back up to 25.

I notice when I disconnect a vac line completely. it idles up. and the short trim goes up at about 10 which makes me this this must be a massive leak or problem to get the long term at a constant 25

For the first time ever I got P1133 insufficient switching for B1S1.

I know I tested it before but for kicks is my PCM/ sensor ground the same as the diagram for a 93? (above the starter)
Every once in awhile I get a B2S2 heat circuit code. Is it possible its effecting them all?
Is it possible this Camaro is actually from the "depths of the underworld"? At this point its making my exgirlfriend look like a saint

This weekend I will do a compression/let down test
 
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