mysterious oxyen sensor - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
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post #1 of 42 (permalink) Old 05-22-2019, 06:03 PM Thread Starter
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mysterious oxyen sensor

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?
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post #2 of 42 (permalink) Old 05-24-2019, 07:23 AM
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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

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post #3 of 42 (permalink) Old 05-31-2019, 01:03 PM Thread Starter
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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
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post #4 of 42 (permalink) Old 05-31-2019, 01:05 PM Thread Starter
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also my MAP pressure with the car off is 14.5 psi... does that seem right?
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post #5 of 42 (permalink) Old 05-31-2019, 05:09 PM
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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.
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post #6 of 42 (permalink) Old 06-01-2019, 10:35 PM Thread Starter
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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
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post #7 of 42 (permalink) Old 06-02-2019, 07:14 AM
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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.
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post #8 of 42 (permalink) Old 06-02-2019, 08:20 AM Thread Starter
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thank you so much man! I'm going to order/make one and post the results. With any luck I might be able to stop driving high on gas fumes.
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post #9 of 42 (permalink) Old 06-03-2019, 07:27 AM
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You might want to carry a fire extinguisher with yo , just in case.
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post #10 of 42 (permalink) Old 06-09-2019, 02:35 PM Thread Starter
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After purchasing a cheap mineral oil smoker on ebay I think I found the leek! attached is a picture of it!
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post #11 of 42 (permalink) Old 06-09-2019, 02:38 PM Thread Starter
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Its a big leek
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post #12 of 42 (permalink) Old 06-09-2019, 02:44 PM Thread Starter
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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!

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post #13 of 42 (permalink) Old 06-09-2019, 02:58 PM
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I've got some spuds & milk, it's time to make some leek soup

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post #14 of 42 (permalink) Old 06-13-2019, 03:42 PM Thread Starter
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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!
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post #15 of 42 (permalink) Old 06-13-2019, 03:48 PM Thread Starter
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These are the reading after 20 minutes of drive time
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