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.

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.

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.

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.