Originally Posted by Glenn101

Okay guys. Thanks for all of the suggestions. I am much better now, after fighting a sinus infection most of the week.
I finally got my brain engaged and did some more diagnostics with Autoenginuity. It has the ability to read specific cylinder misfires so I set it up to monitor all six cylinders. Only cylinders 3 and 6 were misfiring. I have no idea why codes P0303 and P0306 were not being set. That would have clued me in much quicker.

There is a coil pack common to cylinders 3 and 6 but swapping it with another coil pack for a different set of cylinders did not change anything. The misfires stayed on # 3 and # 6. So I trudged down to my local pull-it-yourself treasure yard and relieved one of the junkers of the ignition control modules, and oila! the problem is fixed? (By the way, I did check the fuel pressure. It stays at 49-50 PSI, which is good.)

That answers my question about the voltage output from the downstream oxygen sensor being so high. It was rich. Don't know why the upstream sensor was so low. Once I installed the "new" ignition control module the outputs of both sensors are switching properly. Just hope the catalytic converter was not harmed.

Misfires send raw fuel and oxygen into the exhaust. There was an extensive discussion on IATN years ago about what the sensor actually responds to. Fuel or oxygen. Even with engineers in the debate we left with more questions than answers. At any rate, the misfire drives the front O2 sensor low. The rear should NOT be switching like the front. That would indicate you catalyst is bad. The catalyst degrades with the raw fuel from the misfire. If it'* been running bad for a while it probably ruined the cat.

Thanks again everyone.

Glenn

Originally Posted by Glenn101

Okay guys. Thanks for all of the suggestions. I am much better now, after fighting a sinus infection most of the week.
I finally got my brain engaged and did some more diagnostics with Autoenginuity. It has the ability to read specific cylinder misfires so I set it up to monitor all six cylinders. Only cylinders 3 and 6 were misfiring. I have no idea why codes P0303 and P0306 were not being set. That would have clued me in much quicker.

There is a coil pack common to cylinders 3 and 6 but swapping it with another coil pack for a different set of cylinders did not change anything. The misfires stayed on # 3 and # 6. So I trudged down to my local pull-it-yourself treasure yard and relieved one of the junkers of the ignition control modules, and oila! the problem is fixed? (By the way, I did check the fuel pressure. It stays at 49-50 PSI, which is good.)

That answers my question about the voltage output from the downstream oxygen sensor being so high. It was rich. Don't know why the upstream sensor was so low. Once I installed the "new" ignition control module the outputs of both sensors are switching properly. Just hope the catalytic converter was not harmed.

Misfires send raw fuel and oxygen into the exhaust. There was an extensive discussion on IATN years ago about what the sensor actually responds to. Fuel or oxygen. Even with engineers in the debate we left with more questions than answers. At any rate, the misfire drives the front O2 sensor low. The rear should NOT be switching like the front. That would indicate you catalyst is bad. The catalyst degrades with the raw fuel from the misfire. If it'* been running bad for a while it probably ruined the cat. A normal reading for the rear O2 is about .7 to .8 volts and not swinging.

Thanks again everyone.

Glenn

Originally Posted by Tech II

There is no debate.....an O2 sensor only reads oxygen, not fuel....what happens when you have a misfire? Incomplete combustion, therefore there is unburned fuel AND unburned oxygen coming out of that cylinder.....this excess O2 is detected by the O2 sensor and thinks there is a lean condition....