No pressure in one cylinder

Hi and thanks for using 2CarPros.

If there is no compression in one of the cylinders, it could be the result of several things. A stuck valve, damaged piston (hole in it) and nothing you do is going to change that unless the engine is taken apart, the cause is identified, and then it is repaired. An oil pump will not change that problem. Also, the engine will always have a misfire from the bad cylinder causing it to fail any emissions inspection. I don't know where you live, but in most places that will prevent the vehicle from being legally allowed on the road.

I have to be honest, if the oil pump is bad, there is no oil pressure, and you have no compression in one of the cylinders, I feel you would be better off finding a used engine and replacing it.

If you want, here is a link that shows how to check engine compression. I'm adding it in case you want to check it yourself.

https://www.2carpros.com/articles/the-reasons-for-low-compression

https://www.2carpros.com/articles/symptoms-of-low-compression

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

Now keep in mind. The links discuss low compression and not no compression. If there is no compression, either a valve is stuck open, there is a hole in a piston, or the piston is no longer moving. All of these would require extensive engine repairs.

With all that being said, I wouldn't put money into the engine. Find a good one with a warranty from a salvage yard. In the end, it will most likely be less expensive.

Let me know if you have other questions,

Take care,
Joe