O2 Sensor Lean...Tried Everything - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-29-2008, 04:04 PM   #21
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Default volts

If you put a voltmeter on the battery while running and warmed up you should get 13-14 volts. If so your regulator is OK.
Doing the vacuum plug thing is another good test.
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Old 03-30-2008, 07:45 PM   #22
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I'll give the vacuum idea a try. I'm looking at the data stream from my scanner ie. o2 mv and various sensor readings. I'll let you know what I find out. thanks.
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Old 03-30-2008, 08:04 PM   #23
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I don't want to just jump in, since I'm fairly new to these cars, but it seems that everyone is looking at the probelm as if it'* "too much air" and you seem to have exhausted that issue. How about "not enough fuel"? I know your fuel pressure looked good at idle, and your O2 millivolts had a good range (did you say 150 to 900?) but can you test fuel pressure while driving? You can actually make, or have made, a fuel pressure gauge with a screw-on fitting that will go on your valve on the fuel rail, some high-pressure fuel injection line, another fitting and a water pressure gauge that goes up to 100psi. You can have the fittings professionaly put on the hose at some parts stores (NAPA or other professional stores, not usually O'Reilly or Autozone) so they won't leak. Use some duct tape to temporarily attach the gauge end to the outside of the windshield in your line of sight (safety is paramount), and drive the car checking your fuel pressure. I don't know what your high norm is supposed to be, but you might have a bad fuel pressure regulator. You can also watch the gauge after you turn off the engine. Do you lose fuel pressure quickly or does it bleed down slowly? It should take about a half hour or more to drop to zero. If it drops faster than that your fuel pressure regulator is probably bad. Another thing that can give you a bad reading is a bad MAF. With the car warmed up and idling, tap on the MAF sharply (but don't break it!) with something hard. Does it change the idle in any way? Bad MAFs will do that. Just long-distance guesses--stuff that worked with my Buick.
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Old 03-30-2008, 08:08 PM   #24
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So I checked the vacuum tee plugged it off and no change. So I know there'* no issues there. I'm getting a gasket for the flange between the cat and the manifold to see if that helps but im not holding my breath. I even grounded the O2 sensor to the battery just to make sure it was good. Nothing there either. Hoping on a miracle at this point.
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Old 03-30-2008, 10:05 PM   #25
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Default Re: O2 Sensor Lean...Tried Everything

Quote:
Originally Posted by beaujo700
Ok here'* the deal..I have a 1995 Bonny SSE and am unable to find the cause for the lean signal from my O2 sensor. I have gone through ALLData several times, forums, everywhere. No Luck. Vaccum is fine, fuel pressure 41 psi, idle 750(minor stumble), check injectors, new fuel filter, plugs, wires, maf sensor, IAC, air filter, FPR, battery. Have checked all grounds and cleaned. Any suggestions would be really helpful.
kjhansen57, I agree. But I understood Beaujo already replaced the stuff above, including the MAF. Beaujo, have you already replaced all the items above? If not, there is a quick check on the MAF ... unplugging it and see if the lean error goes away. You may have to have it running when you do this, but I cannot remember for sure. I think you will have trouble starting without it connected. Also, the lean reading is only at idle and not at revs; so would think that checking pressure (41 psi) at idle would suffice.
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Old 03-31-2008, 01:32 AM   #26
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I did replace the maf as well as the pressure regulator...ive checked the fuel pressure under throttle along with rpm drop while disconnecting fuel injectors with IAC disconnected all came out positive. I appreciate all the suggestions, I will check the maf while running just to double check. I also pulled the o2 sensor out of the exhaust and tested it with the propane torch trick. It has to be grounded to work so it was difficult to have it grounded, holding the torch and reading the scanner, but I got a 450mv reading with it grounded while outside the pipe. So..this makes me think issue is maybe from my exhaust leak theory?! Still waiting on donut gasket, but will rule that one out too when I install it.
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Old 03-31-2008, 03:31 PM   #27
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Default lean

Ever run fuel injector cleaner? Just a thought. Does your last emissions test agree with this lean 02 reading?
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Old 04-01-2008, 12:02 AM   #28
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I ran some FI cleaner through it over the past few days..nothing. I'll check my last emissions test to see if o2 was lean. thanks.
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Old 04-01-2008, 11:08 AM   #29
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Quote:
Originally Posted by beaujo700
...Along with that track of tempermental guages is my scanner. It seems to disconnect for no apparent reason while im checking my readouts. It doesn't happen alot but I'm thinking it shouldn't be happening at all.
1. Are you experiencing any driveability or idle problems?
Trying to figure if it is air/fuel issue or O2/PCM circuitry or connectors. You would think the motor would be acting up if it was running that lean. I couldn't find mention of that.
2. With the scanner problem mentioned above, there could be something goofy relating to PCM connections, ground, etc. When you tried checking the G100 ground, was it a relatively small gauge, nothing like a battery ground? Again, of the 2 studs for the ICM, G100 is one closest to the center of the engine. The battery is grounded on the other, closest to the radiator on my 93.
3. Just an idea & may be hard to do, but taking a voltage reading with a DVM at pin 3 of the O2 connector & comparing scanner readout might be of value at this point.
4. Don't throw tomatoes, I would reseat the PCM plugs and leave the PCM on the floorboard... just for grins... so they are not stressed at all ... just to see if it changes anything.
I think the answer to #1 may give us a direction to head. That'* enough arm-chairing from me for now.
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Old 04-01-2008, 11:50 AM   #30
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Default 02

If you truly are running lean the emission test would show a Nox reading through the roof.
I agree that at this point it could be a bad pin or harness in the 02 sensor / PCM circuit or you may check if the spark plug wires are touching the 02 harness wires.
Many on the forum have had drive ability problems because of this.
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