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Old 11-07-2012, 06:44 PM   #1
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Troubleshooting fuel mixture

I have a P0420 code (insufficient cat efficiency) and am trying to isolate the problem. Car idles, drives fine. I do hear very slight emission backfire at 40-50 mph, but hardly can hear it over the radio. I replaced wires, plugs, coil pack recently, and I'm gonna check the injectors tomorrow (with ohmmeter). I think the fuel mix may be a tad rich. Any other suggestions? From what I've read, the O2 sensor is usually not an issue.

'03 Silver SE 155K SOHC
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Old 11-07-2012, 07:19 PM   #2
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It might be more likely that your cat is just no longer doing it's job. You saw from that site you listed that the front sensor should fluctuate fairly quickly between 0-1V (actually more like .2ish-.8ish) DC and the rear should have a pretty steady and consistent reading of .5V DC. This can be pretty easily checked with a voltmeter/multimeter, but you'd need a wiring diagram to tell which wires to backprobe at the o2 sensor connectors. Two will have to do with the heater circuit and the other 2 will have to do with the signal the PCM is looking at.

I think this would be best way for the average guy to look at what the o2 sensors are doing. There're probably youtube videos that'd show you how to do this.
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Old 11-08-2012, 06:46 AM   #3
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Moved to "General Technical Chat".
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