Originally Posted by bonnie_99
Got another check engine light on 99 bonneville. P0300- random/multiple misfire and P0133- O2 Sensor Circuit Slow Response Bank 1 Sensor 1. No vaccum leaks, fuel injectors are working, coils are good, got good spark, new wires and plugs.
When I check the voltage on O2 sensor I get a normal reading of about 450 millivolts out of one of the prongs on the O2 sensor connector but no fluctuation on the other three. Should get a reading from the other prongs. Could the misfire and the O2 sensor be related. Is there more than two O2 sensors? I have been checking the one in the exhaust manifold before the converter.
You have the right O2 sensor. Problems with the back O2 sensor occur about once for every 500 front sensor problems.
With those check messages, you have a chicken and egg situation. Let'* check the bigee first. The O2 sensor is talking directly to the PCM, and the PCM has to hustle like crazy to manage your fuel trims and ign advance.
If you know what codes you have, you must have a scantool. The simplest, crappy one will do. Use it to read the O2 sensor while the car is running.
A good reading from an O2 sensor is one which toggles up and down at sub-second speed. It'* indicating a rich burn cycle, and a lean burn cycle.
The reading should jump (I forget if it'* a whole number or decimal) from around 1 or 2, to around 8 or 9. Back and forth, extremely fast. So fast, you can barely catch the reading at either end.
If it'* just moving from say, 4 to 7, or it'* real sluggish... you are likely to have a sick O2 Sensor. When was the last time you replaced the O2 Sensor?
FWIW, our cars run in a continual state of a rich and lean burn for emissions purposes. There are 2 groups of gases which the cat has to scrub. It needs a rich burn to scrub one and a lean burn for the other. We don't even notice this shifting during operation, it is so minor and so fast.
But it is crucial to the proper operation of the engine. If the O2 sensor is skrewered, it'* sending bad info to the PCM, and the PCM is doing all kinds whacky stuff to fuel, air, and spark to try to get it back to proper ranges.
Make sure your contacts are clean on the O2 connector, and don't let the connector touch a plug wire.
If everybody in the US with a 95-99 3800 changed out their O2 sensor every 40-50K mi, or after their UIM and/or LIM gaskets crapped the bed, we'd use about 1MM less barrels of oil a day. (IMHO)
See what you get.