O2 Sensor Lean...Tried Everything - Page 2 - 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 03-25-2008, 10:56 PM   #11
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So I had to buy the o2 online...much cheaper...Thanks Danthurs! Was half what they wanted at the shop..even with 2 day shipping. I noticed today that there is a little degredation where my cat connects to the flange on my manifold. I think the gasket may have gotten a little corroded from the coolent from way back. Doesnt look too bad but you never know...Is there a way to test if air is leaking into the exhaust and giving o2 sensor a false reading? Im going to get the gasket anyway.
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Old 03-28-2008, 04:17 PM   #12
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So I finally got my O2 sensor (ac delco) as suggested. Installed and checked my Mv, no change still reading 45Mv. I did a smoke test and didn't see any leaks in my exhaust, so I don't really know where to go from here. My short term fuel trim is at 182 and I tried to disconnect my maf sensor to see if it ran better but wouldn't even start. The specs for the maf were in range, but thought id test it just in case, no luck. I'm at a loss and have to get this thing smogged before the end of this month. Please help!
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Old 03-28-2008, 05:22 PM   #13
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PCM?
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Old 03-28-2008, 07:28 PM   #14
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Default I may have to put the old girl down!

I got a known good pcm and connected it to see if there was a change...no luck there either.
I'm out of options it seems. I'm going to write down all of my data readings from my scanner to see if there is anything out of place that I missed. I'll post them here in a bit.
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Old 03-28-2008, 10:16 PM   #15
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I see you checked your grounds. Did you already do G100, the PCM ground point?
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Old 03-28-2008, 10:43 PM   #16
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Quote:
Originally Posted by 93RedSled-SSE
I see you checked your grounds. Did you already do G100, the PCM ground point?
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thats the ICM ground point...not the PCM ground. eh? I'm sure if that wasn't right, the car wouldn't run at all.
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Old 03-28-2008, 10:57 PM   #17
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93 Schematic in shop manual shows "G100" as PCM chassis ground source.
The ICM is grounded through the mounting plate.
The reason I offered that as a check is that it is also on the list of causes for a lean O2 error... guessing an intermittent loss as opposed to a constant loss. Anyway.. I will double check it in a min.

Here we go. I had to reinstall my scanner
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Hard to see the "G100" in the seam of the book... sort of dark and blurry.
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Old 03-29-2008, 01:32 PM   #18
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Thanks for the diagrams. I looked at the ground it shows on the icm bracket and I only have one there. Not sure if 95 differs from 93 but I cleaned up the connector and reattached it. Still showing the same low o2 Mv. The thing of it is that my O2 sensor work with a bit of throttle or acceleration just not at idle. Could there be a back pressure issue with my cat that is causing the low reading? I went through all the vacuum hoses again and didn't see any leaks. I also unbolted and adjusted the exhaust that links the front manifold and the rear. It has a good seal as well. The ground that runs down the back side of the engine (thick black wire) I also moved and grounded to the frame. I also ran a wire and grounded that to the battery just to make sure the ground was solid. Still no change. I'm going to go through and check all my fuses again. Could there be a relay causing issues? If I can get a fluctuation of voltage (lean/rich) with throttle or acceleration then it seems like it should be a vacuum or exhaust issue, but I've checked both and see no leaks. Arrrgh!
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Old 03-29-2008, 01:38 PM   #19
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Not sure if this is possible but I read somewhere that possibly a bad voltage regulator in the alternator can cause weird readings in the system. I tested my alternator with the tester i have on my battery charger and it said it passed but maybe I should get it tested at Kragen with their equipment. Might be more accurate. If any of this is sounding ridiculous let me know. I'm getting desperate and reaching for straws!
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Old 03-29-2008, 03:02 PM   #20
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"I feel your pain."
1. Have you considered blocking off all your vacuum nipples at the vacuum "tree" on the intake? That would 100% rule out any of the vacuum items causing an issue.
2. Outside chance that extra air can be getting in via the PCV since it is downstream in the intake manifold ("straws," I know)

Q: How & where are you monitoring the voltage?
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