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91 Camaro RS V6 - Brand new O2 sensor running lean

We just replaced the upper O2 sensor in my son's 91 Camaro. Before we replaced the sensor the code read it was running rich, now it reads it's running lean. Did we miss a sensor downstream? Could it be that the sensor we just installed is bad?

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  • Tracie Kilbourn Nov 13, 2009

    First the code read the EGR Valve was bad. We replaced that and reset the codes. Then it read the O2 sensor was running rich. We replaced the upper one, but couldn't find a downstream one, and reset the codes. Now it reads the O2 is running lean. The plugs and wires were replaced just prior to the EGR valve. However, one plug was fouled when we replaced it. Could it have fouled out again so quickly? The only symptom is the car stalling occasionally at idle. No backfire or rough idling.

  • Tracie Kilbourn Nov 14, 2009

    Thank you, we'll give the compression test a go and see what we find. I'll also go ahead and maintenance the fuel injectors, I'm sure they could use it. :o)

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Did you clear the code first after replacing and did you replace the spark plugs. If the plugs are fouled the cylinders arnt firing and the excess air is going over the 02 sensor and since it PCM cant command enough fuel it stays lean.

Posted on Nov 13, 2009

  • Ernset ( Skip ) Bouvette

    91 does not have a downstream 02. only some 95 and all 96 and newer. All lean means is so much air is going over the 02 that it cant give enough fuel for the computer to start switching from lean to rich to lean to rich. It does this several thousand times a minute. So from a techs point of view we would make sure the engine is ok, compression test. power thest the ignition sysyem for proper KV's. If the engine is not really running right we would ohm the injectors. Spitting does not burn. An injector must spray and only vapor ignites.. If the ohms arnt the same injectors will need to be replaced. If ohms all the same then a good injector service could help. Once your sure you have no reason for excess air then you can start going deeper.

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There should be an O2 sensor on each side near the top just below where exhaust pipe meets exhaust manifold. The one on the passenger side is a little hard to see and get at.

Posted on Oct 28, 2011

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