Exhaust manifolds and (yet more!) O2 sensor questions
 

So... A '92 VX w/140k keeps creating a CEL for the O2 sensor.

I have performed an A-B-A test with this sensor (in my '95 VX) and it works great! Even got the best mileage ever on a round trip to Chicago -63mpg!

Put it back in the '92 and off goes the CEL.

I don't think it's the CPU as this same sensor worked in this car when I bought it and drove it 250 miles home last year. It did, however seem to degrade in the following months (started bucking). This led me to tear down the IM, TB and such to clean it all up yet did little good. Finally the CEL goes on and it goes into open-loop.

Again, this same sensor works fine in my '95.

The only difference between the '92 and '95 is that the '92 has a non-stock exhaust manifold (from a DX?) that places the O2 sensor further down the exhaust stream.

Could this be creating the problems? Seems like such a small variable but I can't seem to identify any other differences.

Ideas - suggestions?

Thanks!

Pull the code and let me know what code is being saved.
Code 48 teoubleshooting
Code 41 troubleshooting

Will try and check on that this weekend.

Thanks for the flowcharts! (now to learn to use that thing that gathers dust in my toolbox ;)

probably 8 out of 10 times, a faulty 02 sensor code is the result of something else causing the mixture to run rich/lean. the ECU only sees that the o2 sensor isn't switching and thus says bad 02 sensor. However it doesn't know whether the sensor isn't switching because it's bad or because the actual o2 content isn't changing.