Very rich burn......? - 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 05-12-2007, 08:27 PM   #11
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Quote:
Originally Posted by popatim
Did you disconnect the battery to reset the pcm after you installed the new O2?
Yes. This is the 3rd Bonne I have brought back to performance levels. For me, it'* best to let the PCM clear and relearn at many steps. It'* kind of fun to watch the numbers tighten-up and feel the car get lighter and quicker. That'* why I'm so touchy about this rich burn. I knew it was on the rich side when I bought it, but there was some Bob'* O2 sensor in it. I thought putting a new O2 in it was a no brainer to improve it.

The trick to this is finding out how the PCM thinks and where it gets its info. For instance, and this may not be an indicator, if the short term trim has to continually bring down the flow, why wouldn't the consistently positive long term trim be backed down?

I'm going to pull the back plugs. One of the six may show a different burn than the others. There is only one FPR. so the flow through the rail must be balanced in a normal state. Maybe one needs more fuel, so the rest are "flooded". I also got a fuel pressure gauge which says i can measure the FPR and the fuel pump with it. Maybe one of them is sick, and just not dead yet.

The only thing left i can think of would be the coils. I had the battery and alternator tested and they are perfect.

I'll proceed, but I'm hopeful for others ideas or problemsolving routes.

Thanks.
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Old 05-12-2007, 08:52 PM   #12
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Originally Posted by Archon
The "base" voltage for the O2 sensor is 450mv or .45 volts. From that voltage, it can swing down to 0, or up to 1 volt, and should do so fairly quickly. A higher voltage indicates a rich mixture, and a low one, a lean mixture. If the voltage seems to hang longer in the above .45 voltage area, that would confirm your feeling that you are running a bit rich. Was this the same car that had the intake problem? If so, was the O2 sensor replaced prior to that repair?

The O2 sensor works by comparing the oxygen content of the exhaust with a "clean air reference." While investigating this, I found that it uses the wiring for the O2 sensor to sense the clean air around it. So, chafed, burned, pinched or damaged wiring can cause it to malfunction. That would also explain on why it'* important to keep the spark plug wires (#6 being the usual culprit) away from the wiring.

Other things that can cause a problem with the sensor is a leaky or restrictive exhaust system, or an evaporative system problem.
OK, good stuff. The front bank O2 operates in that range and does move quickly. Hard to say if it operates more above the .45v. Does the same median apply to the second bank O2, that one is operating in a narrow range at about .7v..

So wouldn't that mean that the O2 sensor on the cat is seeing a rich exhaust at .7v, which is above the .45v ideal operation? Still within operating limits, but not very good.

That'* interesting about the wires doing the sensing.

FWIW, I was able to check the 2 front O2 sensors against each other. They operated in the same range, except the Delco was much, much quicker than the Bob'* O2 sensor.
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Old 05-12-2007, 11:45 PM   #13
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The same median does apply for the rear sensor, but the voltage swings may be a bit less dramatic...maybe roughly between .3 and .7 volts.
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Old 05-13-2007, 12:13 AM   #14
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The same median does apply for the rear sensor, but the voltage swings may be a bit less dramatic...maybe roughly between .3 and .7 volts.
Then the sensor is consistent with what I'm seeing. I'm operating at, and above, the high end of the normal range.
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Old 05-13-2007, 01:27 AM   #15
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The front oxygen sensor will give you a good idea of how well it can help the PCM adjust the air/fuel mixture. The rear oxygen sensor is for telling how well the catalytic converter is doing its job. You may have a bad cat., or perhaps the sensor itself is going bad.
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