Codes P0300 and B1S2, O2 sensor fluctuating

When you pull the spark plugs on number 2 and 3 what do they look like? It sounds like you have two injectors that are having a spray pattern problem. Here is how to remove the injectors and how to check the spray pattern to see if this is the issue. I have included diagrams below to show you how to use your car as well. Please upload what the plugs look like so I can see what's going on.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Also let's make sure the gaskets for the intake are not leaking, this guide can help:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.

A multiple cylinder misfire is nothing more than multiple cylinders that are misfiring but not consistently.

So, you may be getting 2 cylinders that are counting but they are not consistent enough to set a code for those cylinders.

So, we need to focus on the two that are misfiring. The reason you are not seeing the o2 sensor data change is because it is registering misfires due to not seeing the proper crankshaft acceleration each time the spark plug fires.

So, it may be burning the air/fuel, but it is not accelerating properly. This means we could have a compression issue causing the power to escape and not accelerate the crankshaft like it should.

This means we need to do two things. First, we need to check the compression on all the cylinders and find out if we are losing compression on these two.

https://www.2carpros.com/articles/how-to-test-engine-compression

If we are not, then we need to monitor the intake vacuum using a vacuum gauge and find out if we have intake valves hanging open. I attached a chart below that will help with this.

Next, we need to check for an exhaust valve hanging open and we can use an old school trick by holding a dollar bill over the exhaust pipe and it should feel like it is being pushed out. However, if it feels like it is getting pulled back in at all then that is an exhaust valve closing creating suction.

Lastly since these two cylinders are next to each other, we need to ensure we don't have a head gasket failure between them.

https://www.2carpros.com/articles/head-gasket-blown-test

You can also test this by doing a cylinder leak test.

Please run through all this info and let me know what questions you have, and we can go from there.

Thanks

Did you ever plug the spark plugs to see what they look like?

So, if you have misfires and the check engine light comes on then we need to rely on o2 sensor data. However, you mentioned that the o2 sensors were reading correctly.

This is what is odd. If you have an actual misfire the o2 sensors should be reflecting this. The short-term fuel trims would be rich or lean depending on what is happening. If they are not, then I suspect you have an o2 sensor issue.

What happens is when the engine is running rich or lean, the PCM adjusts for it, and it bases this on the o2 sensor data. If the o2s are not telling the PCM that it is rich or lean, then it will never adjust, and the engine will just misfire. This is the most common cause of only the P0300 misfire with no other specific cylinder's misfire.

So, I would look at the fuel trims and see if they are correct while it is misfiring and if they are then I would suspect the o2 sensors are the issue. If you are getting misfires on only one bank, swap the upstream side to side and see if the misfire moves.

This is what makes me think we have a possible sensor issue. The reason is, why does the downstream o2 sensor see a rich condition and hold it at a rich condition voltage but the upstream is not showing a rich condition.

So, if the downstream is showing rich then the PCM could be pulling fuel and it is affecting 2 and 3 to the point of them starting to actually misfire.

If this is the case, then the upstream should be showing lean if they are reading accurately.

If it were me, I would swap the downstream if the upstream are new and have been replaced since this issue started. However, if they are new and this started after then I would not trust the upstream are accurate.

As for the oil pressure issue, we can help with that, but we need to get a new post started for that. People who have that issue will not find the solution under this post, so we need to start a new one on that issue.

Please let us know what you find. We are interested to see what it is.