Oxygen sensor

Will a oxygen sensor tell a fuel injecter to stay open on the number 2 cylinder of a 99 454 vortec suburban

The first (or pre-cat) sensors will detect if the exhaust has excessive unburned fuel. That info gets processed by the ECM to adjust the fuel:air ratio needed by the engine under the current load conditions. But it will adjust those ratios across that bank of cylinders only.

Keep in mind that the primary reason for these O2 sensors is not performance, it is for emissions control. The ECM would not increase fuel supplied to a single cylinder as there is no advantage to emissions reduction by doing this. It will make adjustments only to limit the amount of unburned hydrocarbons (gas) or limit the production of NOx when the engine is running lean. This is to protect the catalytic converter from being saturated and failing prematurely.

If you have one cylinder that is running very rich then I would suspect that you have a stuck poppet valve or injector.

ok we put it on the computer and it said that the oxygen sensor was bad will that cause it to run to rich on number 2 and cause it to miss out and make it blow black smoke out the passenger side tail pipe this only does it after it warms up but if you get on it it runs out great and you can not tell something is even wrong

If by "number 2" you mean Bank #2 and not cylinder #2, then yes it is possible the bad sensor is causing the black smoke after warm up.

Your truck has four O2 sensors. They work in pairs and monitor each side or bank of cylinders. Bank #1 is the driver's side and #2 is the passenger side row of cylinders. The first sensor of the pair is located before the catalytic converter (the "cat") and senses if the engine is running with too much fuel (rich) or too little (lean). The second sensor is downstream or post-cat and simply checks that the cat is doing its job of cleaning up any unburned fuel and reducing NOx to acceptable amounts.

If the first O2 sensor in Bank #2 is reading falsely lean, it will signal the computer to add more fuel to that side of injectors when it shouldn't, creating the black smoke from the right tailpipe.

The reason you don't see the black smoke right at startup is because there is a short period of time where the sensors have to heat up to their best operating temperature. The computer knows this and will thus disregard those sensors for a set length of time, known as open-loop mode.

I know this is alot info than you expected, but in short, yes, a bad O2 sensor can cause the black smoke. The code scanner should have spit out a trouble code and a description like "Bank 2, Sensor 1 failure". Change that sensor, erase the code and see if it pops up again. If the code DOES reappear, then check the wires going to that sensor.